Author Topic: cryogenic drill bit life extension  (Read 2086 times)

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Online coppercone2

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cryogenic drill bit life extension
« on: September 04, 2019, 09:48:46 pm »


 
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Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #1 on: September 07, 2019, 07:06:35 pm »
Meh. Not much useful info there. He should have done the same test with several as-received drills and noted the variation in tool life. I bet it was significant. As a machinist, I learned to put the final edge on my drills by hand if I wanted good tool life. Most mass-produced tools - especially high speed steel tools such as drills - are not known for high quality edges. Most every one I've encountered has had a burr left on the edge after grinding that the manufacturer didn't bother to remove.
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #2 on: September 10, 2019, 09:43:58 pm »
The funny part is his first side-by-side shows a 20:1 difference. But he acknowledges that the "failure point" is sketchy/subjective. So halfway through he started testing the bits blind.

Except for that first non-blind test, the rest of the tests seems to show little if any statistical difference, at all. From the results, you wouldn't even be able to tell which bit did the drilling, and he doesn't bother to reveal this info (which would just draw attention to the fact the results are nonexistent).* He doesn't seem to acknowledge this. 

Quite the opposite. He doubles down. He observed a 20:1 difference, AND he did blind testing!

*edit: Well, derp. He laid the bits next to the groups of holes, labeled on blue tape as "cryo" or "regular." So he did reveal the results. And the results are not impressive.
« Last Edit: September 10, 2019, 11:15:44 pm by KL27x »
 

Offline GregDunn

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Re: cryogenic drill bit life extension
« Reply #3 on: September 10, 2019, 10:48:04 pm »
He must be an audiophool.   :-DD
 

Online BravoV

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Re: cryogenic drill bit life extension
« Reply #4 on: September 11, 2019, 05:54:10 am »
Wish on his another adventure, using his already built & running air vacuum sputtering rig, try to vapor deposit the already cryogenic treated drill bit tip, with known hard subtance like titanium diboride, its not that expensive, at sample quantity its relatively affordable. That will be interesting to watch, especially for DIYers.

Offline thm_w

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Re: cryogenic drill bit life extension
« Reply #5 on: September 13, 2019, 08:28:37 pm »
Meh. Not much useful info there. He should have done the same test with several as-received drills and noted the variation in tool life. I bet it was significant. As a machinist, I learned to put the final edge on my drills by hand if I wanted good tool life. Most mass-produced tools - especially high speed steel tools such as drills - are not known for high quality edges. Most every one I've encountered has had a burr left on the edge after grinding that the manufacturer didn't bother to remove.

He did do the same test with multiple drills, almost as if you commented without watching the video.

*edit: Well, derp. He laid the bits next to the groups of holes, labeled on blue tape as "cryo" or "regular." So he did reveal the results. And the results are not impressive.

2x tool life is impressive, but for the effort involved is it worth it to a hobbyist, no.

 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #6 on: September 13, 2019, 08:48:07 pm »
Aside from the top two sets of holes, I wouldn't even call it a 2x difference. I'm not a statistician, but for the sample size of 4 sets, what difference is seen looks like it is closer to 20% than 100%.

I would imagine most of the wear in this short sample is because of heat. He had to jack up the rpm to get the bits to wear out fast enough to be practical. This necessitates consistent feed pressure and depth AND timing between holes AND lubricant application AND the plate doesn't significantly heat up. The regular bit might dull a little bit faster in plain steel and then start creating more heat, then die faster. This could be totally valid, but the ratio of holes in this exact test might have very little relation to bit life in practical use.

One other thing he could have done is to remove the mill scale off the steel. The thickness and abrasiveness of that layer should not be expected to be consistent across the plate. Or maybe the mill scale is necessary to detect any difference at all, in this test. The hard oxides mebbe create enough abrasive wear for the subsequent high rpm torture to kill the now slightly duller bits a lil faster.  :-//

Drilling in an abrasive material might have given more sensitive results, not so rpm and/or temperature-dependent. Glass filled nylon or FR-4. Or mebbe a carbide rich stainless.
« Last Edit: September 13, 2019, 09:03:15 pm by KL27x »
 

Offline thm_w

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Re: cryogenic drill bit life extension
« Reply #7 on: September 13, 2019, 09:36:41 pm »
Aside from the top two sets of holes, I wouldn't even call it a 2x difference. I'm not a statistician, but for the sample size of 4 sets, what difference is seen looks like it is closer to 20% than 100%.

I would imagine most of the wear in this short sample is because of heat. He had to jack up the rpm to get the bits to wear out fast enough to be practical. This necessitates consistent feed pressure and depth AND timing between holes AND lubricant application AND the plate doesn't significantly heat up. The regular bit might dull a little bit faster in plain steel and then start creating more heat, then die faster. This could be totally valid, but the ratio of holes in this exact test might have very little relation to bit life in practical use.

One other thing he could have done is to remove the mill scale off the steel. The thickness and abrasiveness of that layer should not be expected to be consistent across the plate. Or maybe the mill scale is necessary to detect any difference at all, in this test. The hard oxides mebbe create enough abrasive wear for the subsequent high rpm torture to kill the now slightly duller bits a lil faster.  :-//

Drilling in an abrasive material might have given more sensitive results, not so rpm and/or temperature-dependent. Glass filled nylon or FR-4. Or mebbe a carbide rich stainless.

The numbers are right there, you don't have to call anything, the average is 88% increase in holes drilled (60 vs 32). If you want to get into throwing out outliers, and actual statistical analysis, then thats fine but not something I can comment on. You can also refer to the papers he referenced, where they found similar twist drill results (as he mentioned in the video):
https://sci-hub.tw/10.1016/j.wear.2006.01.017
https://sci-hub.tw/10.1088/1757-899X/229/1/012014

Sure, mill scale could be removed but some parts will be drilled as-is, as removing the scale is an extra process. It really depends on the part and finish required.
 

Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #8 on: September 16, 2019, 01:55:22 am »
Meh. Not much useful info there. He should have done the same test with several as-received drills and noted the variation in tool life. I bet it was significant. As a machinist, I learned to put the final edge on my drills by hand if I wanted good tool life. Most mass-produced tools - especially high speed steel tools such as drills - are not known for high quality edges. Most every one I've encountered has had a burr left on the edge after grinding that the manufacturer didn't bother to remove.

He did do the same test with multiple drills, almost as if you commented without watching the video.

Way to be a snarky douche. Gold ribbon for you!

The point of my post which you apparently totally missed (almost like you didn't read or understand!) was that the testing method didn't provide much useful information. A better test would have been to test 30 or 100 factory drills and compare their tool life. Having personally used thousands of factory sharpened drills, I have seen a ton of deviation in tool life length. After determining standard deviation in that test then maybe try the cryo and compare.

Small sample sizes are not going to give good information because of variation in drill edge condition fresh off the factory floor. They don't dress grinding wheels for every drill ground - and for those manufacturers that might be using electroplated grinding wheels, the wheels get duller with every drill ground - creating edges of lower and lower quality as they go.

Better still in all of this would be to make a standard sharpening procedure for all drills so that starting condition is not a lottery.

And yes, mill scale is extremely damaging to steel cutting edges. It would have been far better to remove it.
 

Offline T3sl4co1l

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Re: cryogenic drill bit life extension
« Reply #9 on: September 16, 2019, 07:30:54 am »
If the variation were due to mill scale or tool manufacture (don't forget initial metallurgy and composition, too), you would see a larger variation within each population.  IIRC the two sets don't even overlap.  You'll be hard pressed to explain that any other way.

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Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #10 on: September 16, 2019, 01:28:21 pm »
Well for one thing, every effort should be made to provide consistency if you're going to publish a test. For another, there are all kinds of "holes" in the methodology of this test. To the point that I would reiterate that there isn't much useful info to be gained there. Even when he stopped the test on each drill and considered it dull - this is standard stuff for tool life testing. Measure the wear land and stop the testing for each drill when it reaches a certain width. "Listening for screeching noises" as he described it is just silly. Running an elevated speed with no lubricant/coolant is another - no one (I should say no serious machine shop) abuses their tooling this way. To get meaningful test results the tools would need to be run as they would be in actual working conditions.  I could go on...

And there certainly are "cryo" hole sets that are within a few holes of the "untreated" hole sets in his results. Which again is why there need to be far more tools tested.

There have indeed been legitimate tests showing an increase in tool life with cryo treatment. This particular test just isn't one of them. The guy who made the video showed a table/graph of results from one of those tests in the beginning of his video - those were not his results.
« Last Edit: September 16, 2019, 01:47:32 pm by eKretz »
 

Offline SparkyFX

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Re: cryogenic drill bit life extension
« Reply #11 on: September 16, 2019, 03:40:53 pm »
It's a nice subject, though. But what do you do if the numbers of holes required to measure wear increases above test capabilities?
I agree that the method incurs problems, like overheating an otherwise good drill bit, leading to deformation at it's cutting edges until the forces break the shaft. The assumption that wear will accelerate with more aggressive parameters might mean other factors migth suddenly outweigh the one under investigation.

Maybe an automated photo after every hole might have shown the wear on the cutting edge in a timelapse, but that´s a lot of effort to do.

I wonder if the change in grain structure of an overheated drill tip might be reversed by repeating the cryo-process.
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Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #12 on: September 16, 2019, 04:10:05 pm »
It is an interesting subject, no doubt. Any modern machine shop will be using at least High Speed Steel drills. They retain much of their hardness up to red heat and don't lose temper like "plain" carbon steels. Once back down from red heat they are pretty much as hard as they started. Although this isn't very germane to the discussion because if a drill is running at red heat there are other serious problems in need of rectification. Many shops use tungsten carbide drills, which would make this test of no use to those fellows. Most high production CNC shops would be going that route, and getting WAY better tool life than with HSS drills, and at far higher production rates to boot.

The number of holes it actually takes to wear out a drill at proper feeds and speeds is why most home shop guys don't do tool endurance testing. He could have kept the cutting speed to a more normal level and increased the feed, as 0.004" (0.1mm) per rev is pretty low. I would normally run a ¼" drill at double that feed. He could also have switched to a much tougher to drill material.
« Last Edit: September 16, 2019, 04:13:56 pm by eKretz »
 

Offline ogden

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Re: cryogenic drill bit life extension
« Reply #13 on: September 16, 2019, 07:03:55 pm »
I would like to remind that purpose of tests was not about getting meaningful data, but to show cryogenic treatment effect in action. Those who are looking for *data*, shall look somewhere else. Links provided in video description could be good place to start.
 
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Offline thm_w

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Re: cryogenic drill bit life extension
« Reply #14 on: September 16, 2019, 09:28:48 pm »
Way to be a snarky douche. Gold ribbon for you!

The point of my post which you apparently totally missed (almost like you didn't read or understand!) was that the testing method didn't provide much useful information. A better test would have been to test 30 or 100 factory drills and compare their tool life. Having personally used thousands of factory sharpened drills, I have seen a ton of deviation in tool life length. After determining standard deviation in that test then maybe try the cryo and compare.
...
Thanks,

Ben is following the scientific method but has never claimed to be producing results that would stand up to peer review or would be qualified on their own as a publication. A lot of the times he will state that he believes x is behaving in some way for y reason, but is not sure and is open to suggestions.

If another person, presumably with a large amount of funding from an interested party, were to want to do further testing in this area, then yes your advice is good for those people.
 

Offline SparkyFX

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Re: cryogenic drill bit life extension
« Reply #15 on: September 16, 2019, 10:34:18 pm »
Many shops use tungsten carbide drills, which would make this test of no use to those fellows.
Exactly, and tungsten carbide tools of course get better and better, impact resistant and such, there are solid carbide and insert drills. But the drill is just one type of tool, there are plenty others that currently either are not available as such or would not work for the application. If regrinding the drill will remove the effect, it might not be practical or economical at all.

The cryogenic treatment shows that you don´t necessarily need to go the hardening/annealing route, but extend the grain structure reformation to low temperatures.

Think pliers, crimping inserts, bushings. Of course it always runs down to cost, choosing a higher grade steel or the use of such a treatment.
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Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #16 on: September 17, 2019, 02:52:43 am »
Quote
The cryogenic treatment shows that you don´t necessarily need to go the hardening/annealing route, but extend the grain structure reformation to low temperatures.
You don't have to go the hardening/annealingtempering route? You just have to build a cyro-cooler or just go on Amazon and order some liquid nitrogen, you say?  Damn spiffy! :D
 

Offline SparkyFX

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Re: cryogenic drill bit life extension
« Reply #17 on: September 17, 2019, 12:15:13 pm »
:D

There might be other reasons than the effort driven why annealing might be less favorable, like warpage or sooting of surfaces. Though i don't know if the cryo procedure will lead to warpage, if it transforms the grain structure it might warp as well as does heating the part up.
For the unlikely case one develops parts for spacecraft, they might undergo similar changes than in this procedure?!

My comparison was not that good, the hardening/quenching/tempering (thx) route can only set the yield and tensile strength to a certain point, while cryo treatment is extending the direction.
« Last Edit: September 17, 2019, 12:52:51 pm by SparkyFX »
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Offline mc172

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Re: cryogenic drill bit life extension
« Reply #18 on: September 17, 2019, 12:33:35 pm »
Most mass-produced tools - especially high speed steel tools such as drills - are not known for high quality edges. Most every one I've encountered has had a burr left on the edge after grinding that the manufacturer didn't bother to remove.

What you say about deburring the edge after grinding makes no sense. The last thing you want to do is deburr the cutting edge.
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #19 on: September 17, 2019, 08:40:04 pm »
Deburring doesn't necessarily mean to chamfer. After grinding to an edge, a floppy wire edge forms, also called a bur. On most cutting tools it doesn't really matter much and it just falls off during the first couple uses. Honestly, I have never seen one on a new drill bit, but I probably haven't looked for it.

On a razor, it definitely matters. Removing the wire edge is often called deburring. That's what I call it, anyhow.
 

Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #20 on: September 18, 2019, 04:02:50 am »
*forehead slap*

Seriously. :D

Deburring a cutting edge makes perfect sense. A burr left on an intersecting edge will reduce tool life. By how much is luck of the draw. Leaving a burr will result in a folded over edge and a much larger apex thickness when the burr is ripped away during use. Which leads to higher tool pressure and further increased wear rate, etc.

KL27X, I would be willing to bet many tools you've used had burrs. They aren't visible, but they can easily be felt with the edge of a fingernail if you're looking for them.
« Last Edit: September 18, 2019, 04:09:02 am by eKretz »
 

Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #21 on: September 18, 2019, 04:09:49 am »
I would like to remind that purpose of tests was not about getting meaningful data, but to show cryogenic treatment effect in action. Those who are looking for *data*, shall look somewhere else. Links provided in video description could be good place to start.

Ehh, to show "effect in action" one MUST convey data... If said data is not meaningful then the whole exercise is pretty much pointless.
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #22 on: September 18, 2019, 04:41:26 am »
Personally, I think it is a really good video with a good script. Getting to see a homemade cryo cooler making liquid nitrogen. The quick rundown on what it does to steel. The test sample was small and the results unimpressive, but to me that didn't matter. It was still worth the watch. He maybe just subconsciously exaggerated the significance of the results.

And meh. Maybe it was edited that way to make a more satisfying video to the average viewer. Few people who are successful on Youtube care about true education. You don't get there without appealing to the average viewer.
 

Offline ogden

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Re: cryogenic drill bit life extension
« Reply #23 on: September 18, 2019, 11:25:07 am »
Deburring a cutting edge makes perfect sense. A burr left on an intersecting edge will reduce tool life.

Agreed. On the other hand saying that it makes sense does not mean that it is actually happening. Any link to document of tool manufacturer that does indeed deburr cutting edges after sharpening?

Ehh, to show "effect in action" one MUST convey data... If said data is not meaningful then the whole exercise is pretty much pointless.

No. Demonstration of effect is enough, no meaningful data needed. You can't deny that test did show performance difference.
« Last Edit: September 18, 2019, 11:27:28 am by ogden »
 

Offline mc172

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Re: cryogenic drill bit life extension
« Reply #24 on: September 18, 2019, 12:48:35 pm »
*forehead slap*

Seriously. :D

Deburring a cutting edge makes perfect sense. A burr left on an intersecting edge will reduce tool life. By how much is luck of the draw. Leaving a burr will result in a folded over edge and a much larger apex thickness when the burr is ripped away during use. Which leads to higher tool pressure and further increased wear rate, etc.

It depends what your interpretation of "deburring" is. From what you describe, you're actually regrinding the cutting faces to get the burr off, rather than "deburring" it, which as far as I'm concerned is a very light chamfer. Deburring as in the process you to to parts you have just machined with a deburring tool such as a file, rather than deburring as in grinding all the faces to make the edges sharp. :palm:

I find it hard to believe that you consider quality cutting tools such as those from Dormer or Guhring as not fit for purpose out of the box. If your problem is with lesser quality tools then stop moaning and buy proper tools.
 

Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #25 on: September 18, 2019, 10:22:37 pm »
Taken in context, deburring is apt. If you take it out of context that is on you. And yes, I have certainly gotten tooling from Gühring and Dormer with burred cutting edges. Cleveland, Precision Tool, and plenty of others also. Just because you don't notice the burrs doesn't mean they aren't there. Check for yourself...
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #26 on: September 19, 2019, 06:06:15 pm »
Quote
From what you describe, you're actually regrinding the cutting faces to get the burr off, rather than "deburring" it, which as far as I'm concerned is a very light chamfer.
I'm not sure what the confusion was over this. Has anyone even suggested an actual method of removing a burr? I must have missed it.

There are other ways to do it. One is to use a very fine abrasive stone or file, But it's not really what you would call a chamfer. You orient the stone essentially to the same angle it was ground. (In reality you usually are better off to cheat just a little to add a tiny bias towards the edge.*) If the stone is fine enough, most of the burr will eventually fall off. Stropping is another method which is really probably one of the best, if practical. 

As I say, there are other waysl, but "regrinding" the edge wouldn't necessarily do anything but leave the same or larger burr as before. eKretz didn't suggest these expensive drill bits were ground badly. They have a burr, because they haven't been deburred, yet. Even if they are ground, perfectly, that still always leaves a burr.

eKretz: For sure, I believe it matters in a drill. But if you don't deburr the drill, it will still do what it's supposed to. Some people could go a life without ever realizing the improvement they could have gotten... and they might end up spending an extra $128.00 in 2019 dollars on drillbits in their life. So to them it might not matter. But it doesn't matter how infrequently you shave, nor how much you care to spend on razors. If the manufacturer left a burr on, you aren't going to get a single shave without pulling hairs and drawing blood.  >:D

*If you maintain the exact same angle as the originally ground bevel on the tool:
1. you will have to stone until you get partway into the low spots before the burr will fall off, so it will take longer.
2. By the time you do that, you will have formed a new bur.

« Last Edit: September 19, 2019, 07:43:21 pm by KL27x »
 

Offline SparkyFX

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Re: cryogenic drill bit life extension
« Reply #27 on: September 19, 2019, 07:55:20 pm »
Whatever you call it, it will probably be gone after drilling the first hole. Thats what the drill is made for.
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Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #28 on: September 19, 2019, 08:15:48 pm »
I imagine some parts will fold over upwards and just stick around for a long while. Maybe even get welded onto the bit. And as eKretz said, the burr getting ripped off will undoubtedly cause some amount of degradation vs being honed/stropped away. But yeah, average person might never notice what they've been missing out on. (Average person might not notice any difference in cryro, either; depends on the use).

Serious machinist that buys and sharpens a lot of drill bits, it may be worth the time. In this app it makes perfect sense for the manufacturer to not bother with deburring. To do it properly in any automated setup would require fairly frequent tuning, I imagine. It's probably best done by hand, and for a drill bit manufacturer it might be cheaper just to make and sell you non-deburred bit and pass that savings onto you. If you want it deburred, then do it yourself. Or continue to buy cheaper replacement bits and don't bother.

For this test, I think it would help increase consistency if the bits were properly deburred, first? But I guess that might be less applicable for the (majority?) of people that just use the bit how it comes out the box and chuck it when it gets too dull. And meh. I wouldn't call this a thorough experiment so much as a demonstration.

Irony: Seen a guy on YT claiming much better performance when he sharpens band saw blades. He touches a new blade on the bench grinder before even using it. The test is to pull the wood through the saw with a constant weight and pulley, and the best time is "sharper." In this particular case, part of the reason the sharpened blade "cuts way faster" (at least initially) is that he is creating a burr. And this burr essentially increases the rake, due to the side of the saw points he is grinding. The sharpening also decreases the bounce or increases the relief on the other side of the teeth. And both of these changes will increase the speed of cut... for a given feed pressure. You can buy bandsaw blades with different rake for different purposes, and more aggressive rake is generally done for faster/straighter cutting in thicker material. On thinner stock it generally leads to rougher cut for no benefit. You want to avoid having to feed too hard, because this will twist the blade, but it's a tradeoff. So is the blade sharper? Maybe, and it might depend on your definition.

If he increased the feed pressure/weight, the new blade might catch up and still have no issue with blade deflection, and the sharpened blade might run into some issues or speed cap due to rough bites or the gullets not clearing the sawdust.
« Last Edit: September 19, 2019, 09:37:00 pm by KL27x »
 

Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #29 on: September 20, 2019, 03:32:47 am »
Yep, I concur. As I mentioned, most of the folks using drills are not even aware there's a burr present, (and it isn't always, sometimes there's a good clean edge formed - but it's very hit or miss) and are totally unaware of how much efficiency they're throwing away. It's possible to get a very significant increase in tool life (number of holes drilled per tool) by properly removing the burr.

And this absolutely applies to the razor as well. A razor with a very fine wire edge can shave great for the first few strokes or even part of a shave. But when that wire edge tears away, your face WILL know it.

Same goes for the drill. You're absolutely correct that the burr or wire edge will be removed when the very first hole is drilled. And so too will the narrow apex that used to be there. After that burr is ripped away the apex will be much wider and that will result in increased tool pressure (effectively a much duller tool), which will lead to faster wear and an even wider apex, etc.
« Last Edit: September 20, 2019, 03:40:55 am by eKretz »
 

Online coppercone2

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Re: cryogenic drill bit life extension
« Reply #30 on: September 20, 2019, 09:54:04 pm »
if you buy a factory nitride coated drill, can that have a burr too? I get the nitride drills unless they are for hard materials..

I figure if they are going through the trouble to nitride it, they are not going to leave a burr on it?

can someone post some microscope pictures of different drill bit sizes and post optimal looks for what it should look like so people can cross compare their existing drills

a before and after with a burr and a removed burr would make things much more clear.
« Last Edit: September 20, 2019, 10:05:27 pm by coppercone2 »
 

Online coppercone2

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Re: cryogenic drill bit life extension
« Reply #31 on: September 20, 2019, 09:56:08 pm »
as for razors, I recommend if you are cutting boxes with them you cut a few strips of cardboard out and use it as a 'strop' periodically to maintain a edge on the razor.

But, in most cases I think you should invest in the hooked blades for opening boxes.. and then use big sheers to cut the boxes

this is my box destroyer
https://images.homedepot-static.com/productImages/fb78f63b-9f33-40bd-a2dc-887047165f02/svn/wiss-snips-mpx5-64_1000.jpg

They are beefy and long enough that you can torque them sideways while going through a long bit of card board to act as a pry to bend and deflect it so your hand can operate them.

https://www.amazon.com/Stanley-11-983-Large-Hook-Blades/dp/B00002X20T

Not all shears work for it, but those in particular are excellent.
« Last Edit: September 20, 2019, 10:02:00 pm by coppercone2 »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #32 on: September 21, 2019, 03:06:58 am »
My destroyer of boxes is the closest knife. Any of them in my home will do the trick as well as a new box cutter.

I used to buy disposable razor and exacto blades in bulk packages, but I decided to learn to sharpen about time I was around 30. It turns out sharpening is way faster and more convenient than changing and disposing of blades, if you've got the knack.

Hook blades are kinda made for carpet. They dull fast on boxes, cuz you're cutting on the same part of the blade, and because the edge angle is effectively fattened by being in that shape. With a straight blade, you tend to tilt the blade back when slicing a box, and this skew effectively make the edge more acute. Works with planing stuff, too; you want to skew a plane and run it a bit sidewards where you can. This also facilitate some sawing action if the cardboard doesn't slice right off the bat. The hook just don't work like that. It wants to push the cardboard to the point where the blade is more edge-on with nowhere left to phone-a-friend. So it might be the cat's meow for only a short while before it starts jamming and tearing. I went through a phase of making stupid stuff, and one tool was a short and blunt-tipped, deeply recurved knife I imagined would be great for cutting boxes. Not so much.
« Last Edit: September 21, 2019, 04:09:51 am by KL27x »
 

Online coppercone2

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Re: cryogenic drill bit life extension
« Reply #33 on: September 21, 2019, 04:07:14 am »
safety #1
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #34 on: September 21, 2019, 04:10:54 am »
Don't tell me the guy with an oxy-acetylene torch in his garage is afraid to use a knife? :)
 

Online coppercone2

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Re: cryogenic drill bit life extension
« Reply #35 on: September 21, 2019, 08:53:07 am »
they call me mister hook
 

Offline SparkyFX

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Re: cryogenic drill bit life extension
« Reply #36 on: September 21, 2019, 03:21:32 pm »
How big and meaty can that burr be? Are there photos available? I never got a set with that visual, never had them under a magnifiying glass or microscope, either.
The factory grinding will probably be under coolant on an abrasive, which means it will push the relatively hard HSS over a >270° edge. I figure HSS starts smearing the hotter it gets, which you avoid in a manual process by dipping it in water. So... were these drill bits ground without coolant?
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Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #37 on: September 21, 2019, 07:29:06 pm »
SparkyFX:

The burr that is left will vary in size. It can be large enough to see with naked eyes. It can be so fine that it's more practical to feel it.

Quote
I figure HSS starts smearing the hotter it gets, which you avoid in a manual process by dipping it in water.
That's a nice-sounding theory. There is no website or YT video from which you will learn exactly why the burr forms. So the following explanation if from my own personal experience. Feel free to not believe it.


beyond this line, you won't find much corroboration; this is years of my own observation and experience. So I state it like fact, but I might be misinterpreting cause/effect. It's just more convenient to state it like fact than to hedge every sentence.
***********************************************************
The burr formation has nothing to do with coolant or temperature. It is related to the amount of burnishing. What's burnishing? If there's enough pressure, the abrasive cuts. Under that, this thing called burnishing occurs. And it's never 100% cutting and 0% burnishing. There is some mix of each occurring whenever you use almost any abrasive. If the material is cut, the abrasive scratches a chunk of the material away. Where it gets burnished, the skin of the metal is moved but no material is removed. I believe the burr is at least partiallly related to burnishing, because in my experience, the more you make conditions favorable for burnishing, the faster the burr grows. Dull/glazed grinding stone/wheel increases the rate of burr formation. Larger contact area increases rate of burr formation; i.e., if you are grinding an edge using a flat stone, you will find the blade with a wide flat bevel is going to form burr faster than the one with a very thin bevel (this is a benefit of putting a small secondary bevel on an edge on a tool like a chisel. The edge can be honed faster and without creating as much burr.)

Notice I said "rate." How big the burr eventually gets also kinda depends on how much you had to grind and how rough the edge is. If you started with a burr free edge and only grind it a tiny bit, the burr won't grow very big. But if you grind back a lot, that burr will grow longer, but it might fall off by itself in chunks as it gets too long. So it may be limited. Generally the finer the edge, the smaller the burr will be. With a coarse stone, you can make burr that is huge and looks like a string of confetti.

Anytime you grind a new edge on any steel, you should expect to have left a burr there. (Maybe most other metals, too). It happen on a power grinder. It happens when grinding or filing by hand, coolant or no. Exception is with some abrasives, like a crumbly stone that gets a lot of lapping action and surface wear/unevenness, the burr might just about erase itself as it goes... but the edge might also be getting slightly rounded more than it need be. I have a stone that is difficult to make any burr, but it also doesn't make a sharp edge.

IME lapping tends to leave less burr than filing. I think the particles tend to round over the very edge, just slightly. When routing a groove on say a router table using an endmill, the leading and traling edges of the stock tend to cut very slightly deeper, because of flex in the setup. When the bit is only partly on the material it doesn't deflect as much. By the time the entire face of the bit is on the material, the deflection is slightly greater, hence the cut gets slightly shallower compared to the edge. With a fine enough instrument, you can measure it; under enough magnification, you can see it. This is sometimes called "snipe," and if the groove must be exact to the end, you might just start with a longer piece and cut it down after you're done. With lapping I believe something similar happens. The particles at the edge will kinda be free to roll and pop up as they get out from under the edge of the material and wipe a bit of the burr off, I think, but also round over the edge just a hair. Stropping is a perhaps slightly more controllable way to do this, wrappign "around" the edge but using only very fine compounds to wipe away the burr and polish up the edge while making minimal change to the existing edge geometry.
« Last Edit: September 21, 2019, 08:58:52 pm by KL27x »
 

Online coppercone2

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Re: cryogenic drill bit life extension
« Reply #38 on: September 21, 2019, 10:39:05 pm »
do all materials bur/burnish? or at least, all metals of all hardness?

does it happen on some level with oxides?
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #39 on: September 22, 2019, 01:23:53 am »
Quote
do all materials bur/burnish? or at least, all metals of all hardness?
Dunno. I suppose the material needs at least the skin of it to be malleable to some degree. The surface of many non-fully-crystalline solids may contain some "fluidity." In some materials, the forces that bind it together can be a composite of many bonds working over longer and shorter distances. And where the material "ends" at the surface, some of those support beams and girders are not finished. There can also be space between the beams which remain more fluid. There's another thread where Nominal Animal describes how the chrome in stainless steel concentrates itself at the surface. At human temperatures and scale, this happens in a fraction of a second. As soon as you cut a piece of steel away, the chrome will diffuse to the new surface in about an eye blink.

Quote
does it happen on some level with oxides?
I don't know, but i'd take the under on that.
 

Online coppercone2

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Re: cryogenic drill bit life extension
« Reply #40 on: September 22, 2019, 03:09:29 am »
this happens with copper too, if you braze it even with nitrogen it will discolor apparantly because of metal migration of impurities. they recommend low temperature (harris) solder vs hard brazing for this reason when doing copper for HVAC, I think what can happen is the concentration of metal on the surface of the copper that is dissimilar has more propensity to flake off and destroy pumps. they say people think its oxides but its really different trace stuff in plumbing copper that comes to surface. If its joined cold then it does not separate out like cheese left out and behaves as it should. also I think its a process problem with seemless tube production with manganese migration.
« Last Edit: September 22, 2019, 03:15:38 am by coppercone2 »
 

Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #41 on: September 22, 2019, 12:33:01 pm »
Why and how exactly burrs form during grinding and machining is a complicated subject. There are a lot of theories and investigations on the subject but no definitive answer yet. It has been observed that the harder a material being ground or cut is, the smaller the burr will be, but the thicker the root (the part that is still attached to the parent material) will be. So that's problematic for cutting tools like drills because the burr is rarely noticed and as it breaks away it leaves a thick broken edge behind. There is no explanation as of yet that I'm aware of that satisfactorily explains everything going on, nor why on subsequent passes with sharp tooling and exactly the same parameters, sometimes an intersecting edge with a very large burr is produced and sometimes very little or even NO burr will be produced, seemingly at random.

In addition the depth of cut, temperature at the tool/material interface and types of material being cut and doing the cutting all factor in as well. There are plenty more factors too. The metallurgy of the burr and the metallurgy of the parent material are often markedly different as well, especially with higher speed grinding processes. Another reason to avoid cutting with a burred tool.
« Last Edit: September 22, 2019, 12:35:21 pm by eKretz »
 

Offline SparkyFX

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Re: cryogenic drill bit life extension
« Reply #42 on: September 22, 2019, 03:49:58 pm »
I checked a set of drills (new and used ones, top brand) with a microscope-ish magnifier and found a few pieces of burr on the unused drills. They were loose enough to be removed with a fingernail and looked like long, rolled shavings (hard to photograph... but i will try to make some photos in the future). Nothing to worry for me, as i tend to work on softer materials and what i´ve seen will be going the way the chips go anyway. The edges looked sharp enough.

The cutting edge will break down over time, that is a normal mode of operation for any cutting tool and therefore will happen in the middle of any cut.
In knife sharpening the burr is usually removed using e.g. leather, some people hone their cutting tools on stones for burr removal, which as you say prolongs the tool life.

For drills the angle in which the burr removal would need to take place is just hard to reach with usual grinding stones. Small grinding stones used like a file inside the helix might extend life a bit before regrinding is necessary.
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Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #43 on: September 22, 2019, 06:43:50 pm »
Quote
why on subsequent passes with sharp tooling and exactly the same parameters, sometimes an intersecting edge with a very large burr is produced and sometimes very little or even NO burr will be produced, seemingly at random.
If you pay attention to what I mentioned in previous post, you might find this is not as random as you thought. Yes the material makes a difference.

Bur if you actually do a lot of sharpening, keep it in mind. The stuff regarding lapping vs grinding/filing and when grinding/filing the amount of surface area of contact for the grit. Particularly the latter is seemingly completely missing from the radar of pretty much every person talking about this kind of thing on YT. Yeah, I get a lot of info from YT, so take w/e I say with a shaker of salt.

People like their grit numbers.* But that's only the tip of an iceberg. For instance, machinists use 300 grit india stones to finish super flat surfaces. When fully flattened these super coarse stones can't even put a scratch onto a pristine flattened steel surface. They will only remove high spots, say if the part got a ding. This is the far extreme, but it exemplifies the effect of surface area.

It's a very basic thing to understand about abrasives and it is the cause of a lot of this "unknown." It's cuz people do not pay attention to this.

Today, if you hit up YT to learn how to sharpen a razor, for instance, you will 99.9% get videos showing people sliding them to and from on a variety of very fine stones that are lapped perfectly flat. The most efficient way to sharpen razors was figured out by the early 1900's, at least. Solingen Germany was the center of a booming razor industry, and according to the oldest and last remaining company in this business, no company in solingen in this period ever used flat stones to sharpen their razors. Lapping is slow, and once you're past coarser stones like diamond plates, the only thing a flat stone can do to a flat bevel is either burnish or lap (lap if it has loose grit). And lapping is slow. But today, it seems like every person on YT thinks you sharpen a razor by sliding it back and forth on a glossly flat stone 5k times. They even do X strokes. On a flat stone, with the razor held flat against it, doing an X stroke just means you are lapping the tip of the razor more than the heel.

The way the actual Solingen razor companies sharpened (and still sharpen to this day) their razors was on a domed stone. The razor is drawn across the surface, so it's like draw filing. Only a small section of the bevel gets sharpened at a time, which makes this much more efficient. More cutting, less burnishing and less burr, without needing to go to slow lapping process.

The entire sharpening industry is high on lapping/polishing/sharpening combo stones, though. They must have a huge profit margin, these "japanese water stones."*

*The japanese grit scale is different from the american standard, as well. At the lower end the japenese numbers are close to the same. By the time you get to the top end, the equivalent JIS number are about 5 or 6x as large as the AIS ones.
« Last Edit: September 22, 2019, 06:59:27 pm by KL27x »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #44 on: September 22, 2019, 07:19:06 pm »
I did a lot of internet research on the subject or burrs and sharpening.

One curious misunderstanding/myth which highlights the lack of consideration for burnishing/surface area is regarding the ability of arkansas stone to sharpen harder steels. The "science" behind this is that arkansas stone is silicone dioxide, which isn't as hard as say vanadium carbides. But you have to look at the whole picture to figure out why some people can sharpen hard steels on arkansas stone, but others cannot. And it's not because of the myth that all the "good" stones have been mined, and the modern stuff is inferior quality.

The harder the steel, the more pressure you need to cut vs burnish. An arkansas stone is a "hard" rock that doesn't disintegrate and crumble to form lapping grit/paste. It's a lot like a fine file, and there's a reason we don't make files much more than 3/4" wide. The guy that keeps his arkansas stone perfectly flat and uses a sharpening guide will never be able to sharpen a wide single bevel on a chisel or a plane blade made with hard steel. Even if he actually gets the apex on the stone, all he will do is grow a burr. (The "premium" plane blades are usually not only harder but also substantially thicker, which means the bevel will be wider/larger in surface area, too, so you end with burnish/burr, no sharpening.) The guy that sharpens like Paul Sellers, with a convex bevel, will have no problem sharpening that same plane blade on an arkansas stone. And the guy that uses a convexed arkansas stone and draws the blades over it will have no problem sharpening that blade AND keeping a flat bevel.

Grandpa can sharpen that A2 plane blade on his Arkansas stone because he knows how to use it. Today's 20-40 yr-olds learned to sharpen on modern synthetic Japanese sushi mud/lapping stones, and they are applying the same lessons/techniques to the ark stone. Essentially all the searchable info on the web today on sharpening with a stone is derived from the proper way to use these synthetic lapping stones, and a lot of this is counterproductive for a "file stone."

A lot of folks think they're all the same. The guy that knows how to use the hard/file stone will never flatten it. He will never dish it. He will use the stone's edges more than the center, keeping the stone rounded. It will wear from the border inwards.* The mud/lapping stones must be flattish to work. If curved, the grit will just squeeze out around the sides of the small contact area. So they must be sorta flat, and they do naturally dish out during use. That's how they work. They're different animals.

The typical understanding is that the super flat-lapped ark stone is just a finishing stone. You only use it after the blade is sharp. Then it's like that extra special touch; and I have invisible clothes to sell you. Or the "it's only for adding a microbevel." Because when you add a microbevel, the surface area of contact is infitesimally small, it will actually do something. This stone is actually useful for sharpening, if you use it correctly. It won't glaze or dull. It won't be slow or make too much burr; it's actually highy efficient in material removal rate for the fineness and there's no synthetic that appreciably beats it. But you can't learn how to use such a stone from today's web, cuz today's web doesn't know.

*In my research during this curiosity phase, I can across a guy that acquired such a hard ark stone. He described it as curved a bit with about a 20-25 mil curved drop towards either edge, like a loaf of bread. This was obviously intentionally shaped, possibly over many years or even decades, by someone who knew what he was doing. Guy asked the forum how best to flatten it and got lots of help in that regard, and proceeded to flatten the thing and make it useless, again.

Quote
It has been observed that the harder a material being ground or cut is, the smaller the burr will be, but the thicker the root
This is not that mysterious to me. It requires some qualification. There is a limit of hardness that can be reached in stainless steel before large carbides are formed. Up to 0.8% carbon, most of the carbon is used up in hardening the steel. Any amount above that level tends to react with chrome to form large carbide nuggets. So for a razor quality steel, the carbon is typically kept at 0.8% or lower. Those large carbides are surely why the "root" of the edge of "harder" steel tends to be thicker. This doesn't apply to non-stainless steel. In a plain carbon steel you can go higher in carbon content and still keep a fine edge.
« Last Edit: September 22, 2019, 09:23:35 pm by KL27x »
 

Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #45 on: September 22, 2019, 09:27:40 pm »
That bit about the burr on harder materials being thicker but shorter wasn't part of the mystery. That was an observation. If you take the time to read some of the studies done on burr formation you'll find that theories abound. Many conflict with each other and parts of some conflict with or do not fully explain parts of others. It is, as I mentioned, quite an involved subject. As is the heat treatment of steel and its many and varied alloys. And don't get me started on sharpening stones. I lost count of how many I have now. Haven't bought any in years, and am trying to keep it that way!
« Last Edit: September 22, 2019, 09:31:41 pm by eKretz »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #46 on: September 22, 2019, 09:47:25 pm »
If you have a lot of varieties, try to keep some of the things I wrote (and maybe someone even managed to read without falling asleep) in mind.

It is extremely easy to try to make them fit the same mold.

All I ever use on my kitchen knives is an regular arkansas stone with a slight curve to the surface. Takes just a minute to get them sharp. The burr it makes is so fine that I can remove it in a few seconds of stropping on the side of the roll of paper towels next to the sink. And then proceed to shave my entire face. No stropping compound or finer stuff necessary. If you try to sharpen a flat blade with a flat bevel on a flat ark stone, you will make a crazy burr that will take way more to remove and you may never even make the blade sharp. Actually, first ark stone I ever bought sat in a box for approximately 10 years. I thought it was junk, because this is exactly how I tried to use it; like every YT video shows, today. I managed to find this stone the ten years later, and it works just as good as any other I have; it was just a matter of technique.*

Some my other tools I may need to go to a coarser stone every know and again. Hatchet might see the belt sander after it gets a workout. But for kitchen knives, this ark stone is all it takes to keep them sharp for several years, now.

I shave with a straight razor, solely, for several years. I also sharpen it on the same "regular ark" stone as my kitchen knives, about once a month. I usually follow that with a fine ceramic or translucent, but it's really not necessary. I do follow that with a few licks on a hard strop with a hint of compound, then a few more swipse maybe once per shave. That makes a little bit of difference. Without that strop with the compound, there is a tiny bit of razor burn off a freshly sharpened blade. Takes about 2-3 minutes to put a completely new edge on the razor, including the cleanup.

*If it takes an average person many years to notice details like this, and this knowledge is not easily communicated to others, no wonder burr formation remains a mystery.
« Last Edit: September 22, 2019, 10:05:23 pm by KL27x »
 

Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #47 on: September 22, 2019, 10:55:17 pm »
I am well versed in the use of sharpening implements. I have also shaved only with a straight for about the last 20 years. I have used and gotten good edges from just about every kind of stone or hone there is. I usually hone a razor on the stone then straight to a plain leather strop. I don't use paste or spray abrasives on a finished razor edge unless I'm specifically wanting to use a microabrasive-finished edge, which is rare for me. The last one I used was on a HSS straight that I made myself and finished on .05u PCD. I find razor honing to be a good mentally therapeutic exercise.

Here is a photo of my HSS razor. I believe this was T8. I "antiqued" (actually just etched) the blade with some phosphoric acid. The scales are walnut. The stone is a coticule, though the razor wasn't finished on it. There is a "signature" on the shoulder where I nicked the razor while roughing it in on the grinder. It was done quick and dirty just to try it out.

And yes - regarding your asterisked comment and footnote - now perhaps you're beginning to see what I meant about the burrs being there and the vast majority being completely unawares. Sometimes they cause problems,  sometimes they don't. They almost certainly always reduce useful tool life.
« Last Edit: September 22, 2019, 11:14:23 pm by eKretz »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #48 on: September 22, 2019, 11:41:07 pm »
Oh, my. That's a beaut. I have only tried the 4-5 I have purchased. I settled on the Dubl Duck. It, too, is carbon steel. It's got a bit of a natural patina that some of my family refers to as "tetanus."

Quote
I usually hone a razor on the stone then straight to a plain leather strop. I don't use paste or spray abrasives on a finished razor edge unless I'm specifically wanting to use a microabrasive-finished edge
Your entire post was interesting and helpful. And the world is not about me. So forgive me for bringing this back to my earlier post you have maybe dismissed. But...

... If you are honing your razor on a stone the way 99.99% of the currently searchable modern web demonstrates, shares, educates each other to do, then you are doing it on a flat hone. There are some older synthetic hones that are designed to be used this way, and for those, this will work fine. There are modern Japanese water stones that are also designed to be used this way. These hones have loosely bonded adhesive particles which release and form a lapping paste. The Belgian coticule also behaves this way.* Without that slurry, you aren't sharpening your blade. The surface of the stone will be rough and sharp, but as soon as all the high spots start to develop into flats on both stone and steel, the knife wouldn't necessarily start gliding like a hockey puck on ice. But it would do something closer to that, and it would start to burnish rather than abrade.

This lapping action of the coticule is probably why you don't get much of a burr, as you have proven by being able to shave using only a plain leather strop. My strop is hard horse hide, and any itty bit of compound initially (and only that once) that was on there was completely invisible after wiping it off. You only see a bit of the black from steel particles over time. Just an FYI, because it's not a contest. It's for context. :)

*The coticule is closer to the middle, in my own personal opinion. It is a slurry-forming stone, but a bit slow/stingy. It is still hard enough bound for the abrasive to be effectively used without this slurry. If you wash the stone with fresh running water, you can still hone on it. But the issues I have discussed about flatness and burnishing will (I believe) come more into play.

Quote
And yes - regarding your asterisked comment and footnote - now perhaps you're beginning to see what I meant about the burrs being there and the vast majority being completely unawares. Sometimes they cause problems,  sometimes they don't. They almost certainly always reduce useful tool life.
Nope! You were preaching to the choir from the start. I was with you through every word. ^-^ And not that I've gone back to re-read, but I don't recall disagreeing with a word you have said. So I am still with you.
« Last Edit: September 23, 2019, 12:36:31 am by KL27x »
 

Online coppercone2

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Re: cryogenic drill bit life extension
« Reply #49 on: September 23, 2019, 01:02:36 am »
if people say it works better with a bur (does not make sense to me but it seems empirical given the arguments?), is it possible the structure of the metal that is formed by burnishing is some how good for cutting based on its materials properties, despite its propensity to tear out and remove underlying material (like a lever or something)? So it sometimes improves things at the cost of risk to underlying metal being removed and forming a divet? Like that the burr is particularly hard, or slides well, or just does something that helps the cutting process in some obscure way? "sometimes works well but tends to fuck up your equipment'? Or maybe just happens to have favorable geometry sometimes?
« Last Edit: September 23, 2019, 01:06:45 am by coppercone2 »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #50 on: September 23, 2019, 01:38:24 am »
Who says what works better with a burr? The burr is a side effect, not the intent. And in most cases, it is detrimental to have it.

eKretz, I can't find it. But in 2016, I watched a YT video tour of the Dovo factory. The guy who recorded it was a razor shop owner and distributor of a variety of razors and accessories. He was particularly curious about how they sharpened them, since he sold a variety of stones and such.

At that time, the razors were hand sharpened on a 12" long coticule that was shaped nearly like the top say 20 degrees of the arc of a football. A big hump in the middle. He got plenty of footage of a lady sharpening a razor with it. Draw strokes base to tip from the front to about the mid point of the stone. Then left and flip and do the reverse starting at the back end of the stone.

I know the fine layer is only so thick on a coticule, but it was curved enough to use up near all of that layer on the corners of the rectangular-footprint stone. He asked a lot of questions, and they informed them that the sharpeners shaped it like that, intentionally, and they would have to touch it up so often to maintain that shape.

So the coticule is hard enough to be used like what I'm calling a hard or non-lapping/slurrying stone, as well as the way I'm guessing you are using it. According to this shop owner, he remained in contact and was told that they later switched to similarly shaped Arkansas stone, because it required less maintenance, so overall it saved time/money. I don't know how old the video was, so if this is correct then Dovo must have made the switch in 2016 or earlier.

Dovo is apparently the oldest razor company still in existence that has been in continuous operation since it started in w/e century that was. According to the info this guy got on the tour, this is the way all razors have ever been sharpened in Solingen. At one time, it was claimed this was considered trade secret information.
« Last Edit: September 23, 2019, 01:48:23 am by KL27x »
 

Online coppercone2

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Re: cryogenic drill bit life extension
« Reply #51 on: September 23, 2019, 02:09:04 am »
I don't know if he is saying that the operation to remove the bur with a stone destroys the edge by chamfering and its impossible to remove as a post process of 'factory sharpening' or if the bur itself is helpful to the cutting operation (mc###)

it makes me think about grinding and burnishing and if this is an application where finishing might need to be conducted with a unconventional material type (I see there are CBN, AlO2, VC (rare? I swear I saw someone selling vanadium or something grinding wheels), SC and other types of refractory ceramic wheels out there). Maybe one of them smears less during final removal. I always wondered what the odd ball ones were for.



based on what he says it seems like you want to cool it down. I kind of wonder if they sharpen the CNC drills that have holes in them while pumping LN2 through them.
« Last Edit: September 23, 2019, 02:20:40 am by coppercone2 »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #52 on: September 23, 2019, 02:27:27 am »
Quote
I don't know if he [mcxxx?] is saying that the operation to remove the bur with a stone destroys the edge by chamfering and its impossible to remove as a post process of 'factory sharpening' or if the bur itself is helpful to the cutting operation (mc###)
You might want to address that more specifically. Quote some section for context or address mc172. Your posts are otherwise very confusing.

mc172 just misunderstood what was intended by words that can be ambiguous and concepts so insignificant to everyday life that only dweebs like us are still talking about them.

Regarding that short video:
Great, but I think I know a bit more about burr formation than that single two concepts. Maybe I'm wrong, but to me it is so far a pretty obvious truth. The greater the area of contact with the stone, the greater the bur formation. So on the bench grinder, if you grind a chisel to a hollow grind to match the shape of the stone, and slide the chisel only left/right across the face of that stone, you will get a massive burr should you continue grinding all the way to the edge. Even on a wet grinder. This is my contention, anyway. Now if you follow that up by increasing the angle and touching that edge to the exact same stone, you will remove that burr and produce a very much smaller one.* This is presumably because there is less surface area of contact which leads to less burnishing. This is my contention.

You might think that at one point in time at least one other person made this connection. Seeing that "burr" and "burnish" are etimologically related.

*This is not because of the more acute angle. Firstly, this crazy burr will form in either grinding direction, but worse if on the trailing edge. And it will be proportional to the area of contact or wideness of the area of the bevel in simultaneous contact with the grinding wheel. Even if you go and put a 45 degree angle on the sole of the chisel, then come back and grind that deep hollow by pressing that entire bevel across the stone, the crazy big burr will form despite this much more obtuse edge angle.

Another way to reduce the burr formation would be to round over your grinding wheel or reorient your fence to favor one corner of the wheel (then the other, then back to the middle.... ending up rounding over the wheel through use). So that when you run the chisel across the wheel, a smaller slice of it is against the stone. You might think that it should be the same, since that area of contact is still the entire hollow grind, just a smaller slice of it. But it does matter. This will produce less burr, because the abrasive can cut more efficiently. The bigger the area, the more teeth are trying to get their bite. But there are so many going for this bite at the same time they can't quite get their teeth sunk in. And they burnish, instead.

Added to the above: It's not that the metal that was displaced by the burnishing comes from all the way at the back of the bevel to the front, as if you get a cumulative deposit of that area of steel to that section of the edge. This burr forms in every direction where there is a sharp edge; let's say an edge of around 90 degrees sharp or better. And the burr formation is essentially a result of the total area of contact (for that particular material on this particular wheel). So for instance, if you were to cut a few grooves into the bevel, parallel to the edge (and you perhaps widened the blade just a skosh to make up for the loss of surface area), and then you were to grind it by holding the entire bevel against the stone in a perfect mating fit, that nasty of a burr would form on each of those additional edges you created at the ledges of those grooves you cut. Essentially. Holding other factors the same, which might not be the practical case, all of those edges will get the fully bad burr, not a respective fraction of it.
« Last Edit: October 05, 2019, 01:27:27 am by KL27x »
 

Online coppercone2

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Re: cryogenic drill bit life extension
« Reply #53 on: September 23, 2019, 02:36:39 am »
this is solid because most people on this forum are literary worrying about a handful of electrons that don't even stay where you want them unless you are paying for electricity

this bur will last without power, its a serious problem, it probably won't rust off either. at least you can turn a meter/computer off and the ram eventually resets
« Last Edit: September 23, 2019, 02:38:17 am by coppercone2 »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #54 on: September 23, 2019, 05:33:17 am »
It usually won't last too long. It's more a matter of:
1. Does it do damage when it gets ripped off
2. (Flash Bonus Round) Does the size of the burr indicate the quality of the edge, in and of itself.

I suspect the answer to the first question is yes, but it might not matter much.
I suspect the answer to the second question is yes. With grinding/filing, I believe the quality of the burr has corelation to the quality of the edge. I believe burnishing causes the burr, and I believe that burnishing changes the structure of more than just the very surface of the steel. I believe it might cause damage, like mashing the top of the tree to the point some of the roots are disturbed.

I don't know if lapping produces a superior edge or not. But I think lapping tends to remove the burr as it forms, so it might not be a reliable indicator in this case.

The burr can stick around for awhile with say a razor. When using a razor, you don't slice into anything in a way to rip the burr off. In many tools it might not be as critical. It has long been repeated that butchers leave the burr on because it slices meat better. This is older than I am, and I don't know if it's even worth repeating. To me that's just eventual metal flakes in the meat.
« Last Edit: September 23, 2019, 05:35:27 am by KL27x »
 

Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #55 on: September 23, 2019, 06:26:14 am »
KL I am tired and therefore don't feel like selectively quoting your post, but on the subject of the stones beginning to sort of "skate" and burnish as they smooth out - or "glaze" if you will - you'll brook no argument from me. I find this to be true in many instances. There are ways around this as well however - one, as you've already mentioned, is using a slurry. Another is to keep the surface area of the bevel very small so that applied force per unit of area (local pressure) is relatively high. Another is to create a "smiling" edge on the razor,  which accomplishes pretty much the same - and mimics your convex stone approach - without needing a convexed stone. There are more.

On the subject of the strop and lingering abrasive pastes: none have ever touched my plain leather strop. I use separate strops for any abrasives and clean my razors with acetone after using them with those strops before they go anywhere near my plain leather strop. Precision lapping in the machine shop taught me to be very picky like that so as to prevent cross contamination. My plain leather strop has no sign of any black residue on it, and it's nearly a decade old.
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #56 on: September 23, 2019, 06:42:36 pm »
Quote
On the subject of the strop and lingering abrasive pastes: none have ever touched my plain leather strop. I use separate strops for any abrasives and clean my razors with acetone after using them with those strops before they go anywhere near my plain leather strop. Precision lapping in the machine shop taught me to be very picky like that so as to prevent cross contamination. My plain leather strop has no sign of any black residue on it, and it's nearly a decade old.
Yes, you surely are making a very good edge. I have no argument that lapping doesn't make a good edge. Grinding/filing also makes a good edge, but this is where you have to pay attention to more of the details which you and I have mentioned. It's only here where you will see the true extent of a burr and the negative consequences of creating fat burrs to edge quality. The finer the grit of the stone, the less amount of surface area you can get on there without burnishing.

I'm not saying it's the only factor in burr formation. Type and hardness of steel matters. But for the given material and given stone, the thickness/speed of burr formation is related to surface area of contact of the bevel to stone. If you pay attention you will find this to be true. So we (at least I) know more than "burr formation is mysterious and not well understood."

This is conjecture, but I find it intriguing that an entire city thriving on razor and knife manufacturing with a height/boom lasting several decades sharpens their stuff on a hard curved stone and also managed to keep that a secret at least well enough to want to try to keep that a secret. And now that we live in the internet age where everyone has a cell phone, social media, and forums, this knowledge is still basically secret. If you wanted to learn this method of using that "hard" stone in your collection, the one that seems to be completely worthless unless the goal is to make an impressive burr and a crappy edge, you would probably not find it. You will only find a couple redneck stressing how important it is to lap this hard stone perfectly flat. And then to dress it will a diamond plate every few uses to get it to do anything at all useful. It will still be miles from peak efficiency in this weird practice which is obviously not how these stones were used for the vast majority of human history. We didn't have diamond plates way back when.
« Last Edit: September 23, 2019, 07:08:28 pm by KL27x »
 

Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #57 on: September 23, 2019, 06:59:39 pm »
Yes that is true. Theories abound, but there really are no definitive answers. This is partly because there are so many variables involved, as you've alluded to. If there were a definitive solution we wouldn't be having this conversation, because burrs on cutting tools wouldn't exist!
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #58 on: September 23, 2019, 07:16:11 pm »
Quote
we wouldn't be having this conversation, because burrs on cutting tools wouldn't exist
I agree with one thing in coppercone's vid, though. Where the guy says we can reduce it but not completely eliminate it. That's the goal, to reduce it. And if you want to understand how/why they form (or at least understand the factors that affect it) you have to keep track and pay attention to those variables, not just throw your hands up and declare voodoo.

Where you get the point you can wipe the burr off on your palm or plain leather strop like you do, it's indicative of a good edge.

Well, with the one caveat. If lapping, there are some lapping stones that overdo it. As I said, I have one that is so muddy, you can't get a sharp edge; no burr, but also no sharpness. I'm sure there are muddy stones with the right amount to not overdo it. With the coticule, I have read how one afficionado actually titrates the slurry with dribbles of fresh water as he sharpens. His personal preference was to leave it more concentrated to start with and to dilute the slurry for the finish. Dunno if that's just sharpener version of "hint of oak and undertones of vanilla" or if it's actually making a practical difference.

I have no dog in the fight. I wanted to learn how to use the old arkanas stone, and I eventually did. I know for sure that flat lapped coticule and proper synthetics work great. But IME having used them both, grinding is faster than lapping, when you sort it out. And much less maintenance of the stone. So what started out as curiosity and perhaps some romanticism of old fashioned stuff and to some extent "lost" knowledge taught me something completely practical. And it is something that is really not on the web. It's crazy just how much this info is not on the web.

One of the cool side effects about using the shaped ark stone, the oil doesn't wipe off. On a flat stone, with a flat edge, you end up squeegeeing off oil (or water if you like), and the stone dries out faster. Using the curved stone, the layer of oil stays on the stone. I don't like to stand still, and I don't use a bench when sharpening a knife or razor. I just pick up the stone and hold it in my off hand and can walk around or even sit in a comfy chair without carrying also a bottle of oil and having oil dripping everywhere. I've used a stone multiple times over weeks without wiping off and adding more oil. Just when it gets too dirty.





Quote
Another is to create a "smiling" edge on the razor,  which accomplishes pretty much the same
Yes, it does. But there is a fundamental difference. If you sharpen a smiling edge on a flat stone, what spot on this flat surface do you run the contact patch over? You can't get too close the the edge, cuz then you will "fall off" your plateau and dig the blade into the corner of the stone. Anywhere you do it you will put a dip in the surface. And when this dip forms, it will tend to wear faster. Cuz when the blade gets over the dip, it will wear the stone when it run over the back end of the dip. This is in some way related to the reason why perfectly flat stones (and uniformly concaved ones) are rare to find in nature. But very smooth and regular convex stones are plentiful. I'm sure there are other reasons for that, of course. (Like every object is essentially 360 degrees in cross section after you add it up, so more of it has to be convex than concave, lol.)

This dip/wear thing is the reason my stones are slightly convexed in the long axis as well as side to side. It doesn't necessarily improve the current performance. The main reason to ensure continued performance. If you start with the stone straight/parallel in that axis, you will form a dish in the side of the stone. (You are always favoring the side of the stone a bit, because that's where you get the best curve/radius, at least until you wear the stone way down into a dome, and also because that's the only place you can get the heel of the knife/razor onto the stone. Then you flip it occasionally and use the other side and/or use the far side to sharpen just the tip end of the razor/knife). Once you form that dish, the wear of that dished area accelerates. (It is crazy how fast the stone can wear when it starts to dip. You can feel even a super dense translucent stone grind/wear as you draw the edge over the dipped area, and the wear is rapidly accelerated. It's like the stone creates a sharp edge/burr, and then this edge/burr saws into the stone at the back end of the dip where the angle puts the edge into the stone.) If you start with a slight convex dome, any dip is easily worn back out and this problem does not occur. That dip is more self-healing. It tends towards spreading out and disappearing rather than increasing. It took years of use to recognize the extent of that problem; it's significant. You could say the convex shape is more stable under wear/erosion. It tends to maintain that shape. The flat shape is unstable and will only remain flat through input of work. And a small dip over 30% of the flat surface means you have to remove 70% of the stone (and eventually 99.99% as you start getting out the last low spot!) to remove the dip. A small dip in a convex stone, you can wear down just the ends/corners/edge of the stone in that area and the stone is still close enough for horseshoes. It doesn't have to be perfectly symmetrical all the way around to work fine. Small ceramic rods work. Fat ceramic rods work. There is some difference, but it's all good. You just want to avoid dips. The flat shape has only one proper form and furthermore the only way to achieve and maintain it very exactly is through lapping, and lapping is slow*. Also some tools, like a plane blade, need to have a straight edge.

This is all stuff that you can only learn through years of paying attention. And when you die, your grandkid will go on the internet and figure out how to fix all your stones that are out of flat, lol.

*Taking out even a 5 thous dip in a 6" by 2" flat ark stone is not fun. Go to the interweb to watch people do this. And see how many actually finish removing the dip of the noob-used ark stone to the noob-ideal flatness before saying "I could remove the rest, but I don't need to." They just have to avoid hitting that spot forever, should they be sharpening a smiling edge. Every common knife has a belly and will dish a flat ark stone when used in the same way that which is actually proper/ideal for a friable/lapping stone. The friable lapping stone is easily flattened. The ark stone is not.






Thus, I find it so damn interesting that this info is not findable. It's just not out there unless you dig deep and read between a lot of fuzzy lines. So after years of experimenting you might figure out more and more of the reasons that the western world's leading cutlery manufacturing city for 100 years actually sharpens their blades this way, and that it is for good, practical, applicable-to-even-you reasons. But that's where it ends. It's as if the world is dominated (for strong financial reasons and modern thinking of people obsessed with flatness and exact edge angles and thinking that these are essential factors of sharpness?) by synthetic friable stones, and anything you would ever try to add to a more common body of knowledge will just get put in the wrong box and dismissed. Hence, the secret remains a secret despite not being a secret. All "they" had to do was to offer the common person a shinier, flatter, "truer" method that makes more sense on the surface, and ba-ding. They know better.

I didn't learn the dishing issue by being smart. I didn't even learn it by copying what Dovo did to their stone. Like any other idiot, I bought a stone, and it was nice and perfectly machined and lapped into a rectangle, and I didn't want to "mess it up." I started out just rounding only one long edge of it, so as to leave the rest in such a pristine and perfect rectangle. And after a year, I learned why this is undesirable. That edge of the stone turns into a saddle shape, and the wear accelerates and doesn't do any favors to trying to get a good edge. So in the end, the ideal shape is very nondescript, not perfect in an ideological sense, and looks like not much thought or effort went into it. It's just sort of rounded everywhere and the opposite of sexy. I have a stone that is kinda shaped like a pentagon in outline, and simply judicously rounding it works just fine. I can draw a blade over the the corner where 2 sides of the polygon meet and and it doesn't matter. The corner is dropped a farther, and the line the blade follows turns into a gentle curve rather than a sharp turn. W/e shape the stone starts at, you just have to round it over a bit on all directions, which is very easy and why stuff tends to get rounded over by entropy, naturally. Just w/e there is a straight line, in any axis, get rid of it by working down either end. If the the beginnings of a dip (or too much straightness) start to develop along a long axis, I can just turn the stone and sharpen over the corner, same drawing motion. The "imprecision" of all this just creeps out the modern world. And it lacks the distinguishing features of a successful commercial product. It doesn't have a "new car" aspect that is easily lost and difficult to regain. It doesn't wear out (or it at least takes generational cycles of kids "fixing" then later "unfixing" these things to wear them out). It is a commodity that is not easily branded.
« Last Edit: September 23, 2019, 11:58:10 pm by KL27x »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #59 on: September 24, 2019, 12:50:46 am »
Quote
https://youtu.be/3ACJrAI3SxM?t=247
Interesting that this vid shows what looks like the "normal" use of a muddy looking synthetic or perhaps coticule?

The video I watched was not like this at all. If you watched something like this, you might think I have a fanciful imagination or I'm a liar.

After looking around, I'm pretty sure the guy that posted the vid was "the superior shave" guy. And the lady sharpening was much faster. She was sitting at a table, not standing. And the razor moved like a blur. It was not a professional done video, just some footage from a guy that talked up with the people on a factory tour, and then posted vid with some details in the video description.

Not only that, but he has posted video showing him recreating this curved stone. He "sacrificed" a much smaller piece of coticule for this experiment. And he went way overboard. I think he obtained a piece of granite or something with a gentle dish it in, and then he lapped the coticule with the granite. I don't see either of these vids in "the superior shave" guys videos, but I am pretty sure it was him. I remember distinct details, like the coticule was only about 4" long (yeah, it was painful watching him try to sharpen a razor on this short a stone), and the fine layer got so thin on one end that when he was done it had worn through in a spot near that end, revealing the coarse layer underneath. He pointed that out.

Perhaps the secret guild of illumiati stone cutters saw it and got Dovo to ask him to take it down. Or perhaps his viewers complained how stupid this was and that the stone has to be flat and/or he got tired of talking about it to the people buying expensive coticules from him.

Or maybe Dovo customer support costs increased due to people calling in and asking about the video. And complaining they can't recreate the Dovo edge if it's made on a hoky hand-shaped humpback stone, and if that's how they sharpen them then where can they buy this hand-shaped stone for themselves?

OTOH... he is making convex arkansas stones for sale. So yeah, it was definitely this guy. Just I don't see these two exact vids.


The way I do it, I'm not concerned too much about the center. I would blend it in, but I wouldn't care too much if it gets nearly flat there. I just would use it in a way that the wear is around the edges, and the stone gonna get there by itself, eventually. An 8x3" is a lot of shaping and a huge workout to get the entire thing to a decent curve, even using diamond plates.

Actually, if you take your precision flat ark stone and rub it on a flat piece diamond plate or a piece of sandpaper adhered to a precision flat granite... guess what. You won't put a scratch in the center. There will be a bare oval area that doesn't get touched. About time you reach the point where the scratches reach all the way to the center is where I'd be done curving the middle, and it looks like maybe he is doing something similar, although knowing his previous video I bet he precision ground the glass to be dished, too, lol.   

Addendum: in fact, I know his lapping plate is dished, just by seeing the frame of the scratch pattern on the stone. His untouched spot is the entire third of the stone lengthwise. If he were doing this with the sandpaper over a flat platten, the oval would match the outline of the stone. Starting with nearly the entire surface, then receding from the borders at essentially the same rate. It wouldn't shrink from the ends of the stone, only. This is assuming the stone started out flat, which is pretty safe to assume from my experience with a few stones from common sellers. I think it would be harder for a manufacturer to not make them flat, these days.
« Last Edit: September 24, 2019, 02:25:59 am by KL27x »
 

Offline eKretz

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Re: cryogenic drill bit life extension
« Reply #60 on: September 24, 2019, 07:19:18 am »
Yes I know that guy, IIRC his name is Jared and he does use a concave plate for shaping those stones. There has been a considerable amount of discussion regarding his convex stones at razor forums. Personally, for razors I will stick to flat honing surfaces and a slightly smiling edge. It is easy to renew the surface of a flat hone/stone, and checking for flatness is much easier than trying to reset a large convex surface - there's no easy way to check such a surface for correct radius throughout - unless you do like Jared and make a concave master to use with wet/dry.

And yes you are correct that there isn't a lot of info out there on the subject of proper use of some sharpening stones. For quite a lot of years even a large percentage of the guys on razor forums were saying that Arks were no good for razors.That's just bunkum. I started with an Ark I got from my grandfather and used that stone for a very long time before starting to collect, use and experiment with others. Arks are excellent razor stones.
« Last Edit: September 24, 2019, 07:22:19 am by eKretz »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #61 on: September 24, 2019, 09:07:23 pm »
Quote
It is easy to renew the surface of a flat hone/stone, and checking for flatness is much easier than trying to reset a large convex surface
When the stone is appropriate to this type of use, then yes, it is easy to maintain it flat. Your coticule is way more friable than an arkansas stone. It is a "tweener" stone and can be used flat or curved. Many more friable synthetics cannot be used curved and have to be flat. If you tried to curve them (I have tried everything), the curve makes the lapping paste just push away from the contact area. The small contact area erodes the soft stone very quickly making more paste. And the stone does not work well or hold its shape and will eventually conform to the shape of the blade and start working again, but you just wasted time and stone. It's with the ark stone in particular, and perhaps some other harder stones like slate, and the hard sintered ceramics which really don't work as sharpening stones when they are flat lapped. Some folks have granted them a mythical position of "finishing" only, and some people use them flat and can still sharpen stuff on them because they unwittingly have developed the habit of favoring the edge just slightly. But they could do much better in either case.

Quote
- there's no easy way to check such a surface for correct radius throughout - unless you do like Jared and make a concave master to use with wet/dry.

Despite Jared being very careful to precision grind his lapping plate into a perfect sphere, it is not necessary just because he thinks it is. Well, from a marketing standpoint it is actually great, and I'm sure his customers are in awe to receive such a perfectly spherical shaped stone.

I understand completely that if you put a razor on a stone, the curve/radius of that stone affects the sharpening angle, just a tad. If you increase the radius, you will start hitting more on the apex. And if you decrease the radius, you will start hitting more on the back of that bevel. But the differences here are minuscule*. The main reasons to curve in all axes is to reduce the area of contact and ensure the entire surface is being of the stone is being used, one spot at a time, to retain a regular surface with relatively sharp particles. And IMO one of the other practical purpose of curving the stone in the long direction as well as side-side is wear pattern. That is my experience. You want the stone curved enough to be able to handle normal wear without tending towards developing dishing. Is does not have to be spherical all over, and I actually wouldn't want this on a long rectangular stone. I would prefer it have a tighter radius side to side and a larger radius end to end. Hence to end up with something more like a section of a football. That's just my personal preference.

Flat stone, anywhere you put wear on it, ba-ding, you have a dish, and the wear accelerates. Curved stone, anywhere you put wear on it... it's a little flatter there, but still no dish. And where you put this flattish spot, on either end there's now a bit more radius and those spots will wear faster, returning the flat spot back to curved. Self-maintaining, glaze never happens, stone cuts more and burnishes less, no wasted hours of trying to flatten a stone so hard it doesn't want to be flattened.

Quote
Yes I know that guy, IIRC his name is Jared
This guy's demeanor is awesome. He's just so disarming. AFAIC, he lulled Dovo employees into giving up trade secrets, then they later got him to take down the video. :)

*The important thing is the the stone will cut more and burnish less. Wherever it does grind the bevel it will be able to cut. And this means it will be able to reach the edge, even if it has to cut a bit more from the back of that bevel (because maybe you used a flatter stone to set the bevel) it will cut that down and keep cutting until it reaches the apex. If it doesn't hit the exact spot on every pass, it is of no consequence, just that when it does touch the apex it is not burnishing and decreasing the durability and sharpness of the edge. When I first started to use these stone, I followed the info available to me. If you use it the way most people do, this just doesn't work. It only can add a slight microbevel, at best, by lifting the angle and touching only a small area of steel to the stone. If you ran the blade over the stone and weren't hitting the apex due to difference from the pervious coarser (actually doing-something-useful) stone, then the apex would never hit no matter how much you slide the blade over the stone. Most all you could do is eventually grow a burr and still have a bad edge. This is especially true of the harder black and translucent stones.  Once you curve the surface, they are no longer a mystical burnishing/finishing (the blade was razor sharp , already, but can you feel the difference after watching me do 1000 passes? No? Well, I can!) stone. They sharpen things. They will put on that razor edge from nothing, if you have the time. And no that is not the case if this stone is flat; given infinite years of labor, it will still not produce a very sharp edge from dull... well, unless you finish with more obtuse "micro-bevel" passes to cut off that burred and mucky steel from the edge. IME, you need to raise the angle about 30-40 degrees for this to work on a flat ark stone.

There's nothing "wrong" with doing this microbevel, but it is necessary due to the burnishing going on. When I first learned to get a sharp edge with an ark stone by doing this high angle microbevel, I thought it was wonderful. I mean, I finally got a razor edge off this stupid stone. Maintained my kitchen knives on this flat ark stone and it is all great, at first. But fast forward 4 months later after you've repeated this procedure 4 times, and all your knives are still razor sharp?... but that edge starts to flop and fold over, and now you need a proper sharpening stone. One of the first things you might have noticed is that the burr isn't being removed by the high angle microbevel passes, anymore. Not as easily. The distinction between burr and edge is blurring, and you have a burr-edge. Used the way everyone else uses it, the ark stone is extruding a bunch of weak metal into the apex through burnishing, so it is good for "light maintenance" until the edge turns into a limp biscuit. With the curved stone, the edge is sharp at any angle you want to sharpen at, and the burr just falls off on your palm, and it's a hard, durable, new edge everytime. To some of the most prominent sharpening and vocal students/enthusiast/experts on the web, it is considered normal to have to grind the edge at 90 degrees and start over, every now and then. Some claim they do this every time they sharpen; and I've even heard a strange technique called plateau sharpening. But I'm telling you, if your stone has a high cutting:burnishing ratio, this is not necessary. It will remove material without extruding as much new burr, revealing a fresh edge.

**There's really no other good way around this. For the "hard" stone to be able to cut that steel without burnishing so much, it has to have widely dispersed cutting points with some more breathing room between them. But the finer the grit, the closer those points get to each other. Diamond plates can be engineered to do this to some degree, by altering the distribution of the abrasives. This is similar reason we don't flatten stuff to a fine finish with a giant belt sander. We plane them with a blade that rotates in an arc and cuts a tiny section at a time. We run them through drum sanders and surface grinders and such. Tiny areas of cutting.

Also, IMO, the true hard (surgical black and translucent) ark stones still burnish a bit more than ideal even when convexed. For a hard hone, sintered ruby is a bit superior in this grit/fineness range. But the true hard arks are pretty close to a no hassle sharpening stone when convexed.


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BASIC INFORMATION (that in hindsight I should not have assumed is commonly known.)
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It's not like you burnish the steel and make a burr, and then at some point you've burnished all the weak steel away from that surface. Initially, most of the metal may be the "looser" or "unimportant" stuff, but removing it exposes the important structures. These come tumbling down, and the burnishing continues. That metal just keeps oozing/flowing out past any acute edge connected to this area being burnished (the contact patch), namely the apex of your blade. If the contact patch ends over a flat surface or end in an obtuse angle, any of the burnished metal flowing there will stop, because it's supported there; it has more interaction. It has buddies saying "hey don't jump off that bridge, yet, cuz we're having a party." But over the acute edge, the burnished metal just happily flows right over.

So it's important to understand this bit:  the burr is not a bit of metal leftover after grinding in the apex. It is not formed through a subtractive process. It is being constantly extruded. It grows. These pressure points of the abrasive pushing into but not cutting do some kind of japanese pressure point kung fu to the steel, and parts of the metal temporarily act like a fluid. To get a sharp edge, you want a stone that will cut the burr away faster/better and grow new burr less quickly. If you have too much burnishing and too little cutting you cannot get down to "good" steel unless you go 90 degrees to wipe the edge off and start over, and you can still have issue by the time you form a new edge (and this is where Cliff Stamp's "plateau sharpening" theory comes in to save the day; the theory is to cut off the edge at 90 degrees, then sharpen it only until the edge becomes nearly sharp, but stop before the burr gets all the way to the apex. But if you use the proper technique, of which there is more than one, you can forget anyone ever came up with this. When it comes to the methods that aren't lapping, this essentially boils down to controlling surface area of contact when on the edge. Make the bevel smaller or reduce area of stone touching the bevel).

The burr could be considered as a glacier flowing over the edge of a cliff. If it flows faster than it is ground away, it will obscure the riverbed below, and the apex you make is made out of the glacier. If you can remove it faster than it grows, you can grind an edge into the riverbed, proper. This burnished, fluid metal is covering the entire surface of the blade, both sides. It's just where it is allowed to flow past the edge, there's no "solid" steel underneath it, anymore, and it's all burnished metal or burr.

The surface of steel always has this crappy stuff on the surface that is not as strong. This why you can't completely remove the burr. When you expose that new edge, the surface will still be relatively weak. But you have the minimum thickness of this weak stuff. Unchecked burnishing at the edge will thicken this layer of weak metal.

It's not that this info isn't out there. It's just the signal to noise ratio isn't very good. Due to internet experts like me, except some of us got it right and the rest got it wrong. When everyone has a say and everyone has feelings, truth is a popularity contest and everyone gets to be right.

It is obvious to me what most people are doing with the flat lapped arkansas stone (and/or flat sintered ceramic stones). You have 3 basic categories of time-wasters.

1. The "finisher."  The "finisher" makes an actual sharp edge on a friable lapping stone. This slightly rounds the apex and produces a razor sharp edge. They then "finish" the edge on the flap lapped hard stone. This burnishes the bevel, refining the scratch pattern. And because the apex was slightly rounded by the lapping stone, they can stop before pushing burr all the way to the apex and/or they are putting some lapping compound on the stone. The notion that the scratch pattern on the bevel is what makes a blade sharp is ridiculous. The apex is what makes a blade sharp.
1.b. or he uses another stone or abrasive to form a slurry on the stone.

This is the kind of guy that talks about lapping hundreds or thousands or times on a razor that is already sharp. His favorite 2 words are "JNAT" and "slurry." Indeed, there are people who believe a slurry is the only way to get a blade sharp, despite people have sharpened knives, machetes, swords, and axes with files for centuries. If you sold this guy a block of glass, he would find it exquisite. As long as you charged him $200.00 and told him it was a rare natural stone from Japan.

2. The "microbeveler." This guy takes the already sharp blade, and he burnishes the bevel to polish out the scratches. But he doesn't stop before the burr gets to the apex. So he does a high angle "microbeveling" pass on the flat lapped stone to cut the burr back and reveal a good apex.

A good example on YT is Richard Blaine. I believe he sells kitchen knives and sharpening accessories. He demonstrates this way of using a flat ark stone. Ironically, he demonstrates the difference between the "western stroke" (more of a drawing stroke) and the "eastern stroke" (back and forth shush-shush slave labor on a sandy stone). I believe the difference stems from using hard/file stones vs lapping stones, the former benefitting from a drawing motion over a smaller area. But he fails to make that connection, and his version of a "western stroke" has the rotation but has only minimal drawing motion.

3. The unintentional curve guy: This is the guy that may or may not lap his stone truly flat. But when he sharpens, he is intentionally or subconsciously favoring the edge of the stone when on the straight part of his knife and is drawing the blade across the edge of the stone. When he gets to the belly/curve, he starts to lift to get onto the flat of the stone and that's fine, too. Then this person will typically periodically re "dress" the stone with a diamond plate, to take out the dip/wear and this actually maintains a slight curve to the stone. This is the guy that is actually sharpening the most efficiently of the 3. But he erroneously thinks the stone must be "flat" and that flatness does him any favors, and he is wasting a bunch of time to maintain the stone in this "flat" shape. He has learned how to get the best edge using the wrong paradigm for the stone, because everyone else is doing it.

Good example on YT is Jeff Jewell. He is just some guy posting videos with no financial incentive, AFAIK.

The first two guys are just wasting time. And if this is the only stone you had, you could not maintain an edge doing just this no matter how delicately you use the blade and/or how often you touch it up. The burr would eventually push out into and become the edge. You would have to use an actual sharpening stone and/or to cut the edge off at 90 degrees, periodically. The third guy sharpens great; he is just delusional.

The reason I use a strop touched with compound following sharpening of my razor is not to remove the burr. I don't need anything special to do that. It is to polish over the microserrations on the apex. These microserrations are a natural result of sharpening on the curved hard hone, and in most cases they are advantageous. On a razor, they can cause razor burn, cuz you actually angle the edge towards your skin. Right off the stone (convexed translucent arkansas or ruby), I can strop (a razor or any thin knife of decent razor steel) a few times on the edge of my hand and get an amazing, very close, very nice shave without cutting myself. By most objective criteria, this could be the best edge, possible. The closest shave with essentially just a single pass without missing any hairs. But 3-4 days of this in a row and some areas of my face have been thoroughly exfoliated and can start to get a bit of sting or burn. A few swipes on a strop with compound guarantees this doesn't happen. Any stone that burnishes too much will obscure these microserrations; this is where you get a razor sharp edge, but after little use it can't cut a tomato.*** Only a stone that has a high nuff cutting to burnishing ratio can form/reveal these microserrations in the "hard edge." The other reason to use a bit of compound is to remove the new schmoo that forms on the edge over time. A bare leather strop just pushes the schmoo back into place rather than remove it. The blade will be re-aligned, but it will require more frequent stropping as you go, because the edge will get weaker each time and get more quickly out of shape. Before figuring out all this stuff I used to have to re-sharpen my razor more frequently. The more you learn, the less work you have to do. On most blades, other than razors or chisels and plane blades, I don't use a strop with compound. The reason I use compound on chisels and plane blades is because those tools are only sharpened on one side and the flat/unsharpened side tends to develop a bit of back bevel through wear. It's not always worth it to me to grind this tiny wear-bevel all the way out every time I sharpen these tools. I hone the flat side but maintain within a couple degrees of flat. The apex might be only 80-90% complete (still sharp enough for most things), so there are usually parts of the burr that don't come away with a bare strop. Micro chips/scratches that go to the apex get filled in with burnished metal, so the burr has spots of thicker root that doesn't separate, easily. Compound gets in and cleans the burr out of the low spots in the apex, so that the burr will come away.

***This is exactly the kind of edge you make on a flat-lapped arkansas stone. Stropping with compound makes such an edge actually sharper. In this case, the strop is removing some of the burnished goo to reveal the hard edge, warts (natural serrations) and all. And the edge gets some bite and lasting sharpness. In the case of sharpening on a curved ark stone, the main reason to strop is to smooth the edge. The strop doesn't make that edge appreciably sharper, cuz it's already good to go. Except for shaving. If you were to try it, it just might change your perception of what the burr is, and it might give you better insight into what the hocus pocus you might have learned from others is actually doing and why it is "necessary" in the first place. When I say "you," I don't mean you, eKretz, but anyone else that might be reading this. There is some case where the smooth burnished bur-edge is desirable. Some of the eye surgeons of old experimented with burnishing steel scalpels and claimed this decreased healing time and reduced scarring of the cornea. And that's fine, cuz an eye surgeon doesn't cut very much, if he's doing it right. :) But for most things, including even a razor, any of this "smooth peanut butter" filling in the valleys in the apex just reduces the useful life of the edge.  If the apex isn't perfect to begin with, the flat lapped ark will make scratches and voids/chips disappear - by filling them in with goo. This is mostly cosmetic and it degrades the edge, in a way. Keep on sliding that bevel over the glassy flat stone, and you will just extrude more burr over the apex. The convex ark will keep on cutting until those defects are removed and replaced by the finest defects it can leave behind. Once it has cleaned up all the apex and reached most of the original low spots, any tiny burr fragments that are still clinging to the apex will fall off if you even look at them wrong.

Lapping stones can automatically do what the strop with compound does. You shouldn't need compound if you use a coticule, properly. That is a stone that just happens to have the properties to give a good shaving edge, right off the stone, when used right. But for maintenance between sharpenings, you might find a bit of chrome ox will extend the life of your razor better than a plain strop. The plain strop will tease off a fine burr immediately after sharpening. And it will realign the edge as it takes damage through use. Add a bit of chrome ox, and it does these two functions plus is removes new schmooey metal that forms over time and becomes part of the edge.
« Last Edit: October 10, 2019, 09:20:52 pm by KL27x »
 

Online coppercone2

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Re: cryogenic drill bit life extension
« Reply #62 on: September 26, 2019, 08:58:13 pm »
in regards to weak steel particles scattered on the surface, can it be etched away with acid prior to sharpening in order to reduce the complexity of the sharpening operation (this is getting hairy)? like increase roughness but decrease burnishing if one species is susceptible to making valleys on exposure to acid that leave the non burnishing part elevated?

\perhaps some kind of chemical/peening/ultrasonic/(laser blasting??) process (or mix of multiple processes like acid etch in ultrasonic) can etch/remove this from the surface some how prior to the final sharpening step if done carefully?

re-heat treatment maybe like induction edge hardening, even if its already hardened? or thick nitride deposition and diamond sharpening (where the nitride acts as a gap filler or something on the weak steel?)

with healing I think the increased surface area of a cut allows for easier coagulation/platelet buildup, so you want a 'rocky coast line' for healing I think.. the platelets should have anchor/'safe harbor' points to attach to I think? a ship is happier in a natural harbor vs the side of a  concrete city sea/lake-wall (vertical sea walls are just fucking creepy anyway, all the good dams have their walls built like zigarauts now to reduce this effect IMO).
« Last Edit: September 26, 2019, 09:10:14 pm by coppercone2 »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #63 on: September 26, 2019, 09:22:10 pm »
1. In theory? Maybe, maybe not. The "fluid" surface metal is still interacting with the solid steel. If you "surgically" removed it bit by bit, the remaining structure of the surface may no longer be stable. There might be a minimum amount of it, anyway, that is necessary to be there. And even if the surface was stable, as soon as the exposed structures of this surface are damaged during use, then this "releases" a new layer of this fluid surface. The surface turns to this fluid metal, that flows like a glacier under pressure, again. I think of it as a surface effect of steel. Steel can't be good at everything; it's very strong, but where it just "ends" some of the things that make it so strong don't have anywhere to attach/finish. Just cables going nowhere. Well, many might form alternate bonds, but end result is the surface has a different structure than the interior.

So if you press hard enough on the steel through small points of localized contact, e.g. burnishing, you can damage the solid steel underneath and make this layer thicker. (More accurately, maybe the layer is only ever very thin where it is being formed; but it CAN definitely be moved/flowed and become thicker in another area). But there might be a minimum amount that is always present.

2. Yeah, maybe laser. Sure what not? Etching a file in phosphoric acid is said to sharpen it. And it's not just a home-remedy folklore. There are businesses that offer this service to other businesses, along with other sharpening services.

3. Perhaps modern nitride coating already effective achieves this? I dunno, but it sounds plausible to me.

4. I dunno about this. I have heard it both ways, that a cut heals better/faster if the blade is sharper/smoother. This is what I tend to believe. The closer we can put humpty back together, the less new tissue has to form to glue it back together. Like putting a broken vase back together, kinda. I cut my finger once where it wouldn't stop bleeding for a day or so. That was a very sharp knife, but I think the bleeding wouldn't stop because I hit an artery. :)
« Last Edit: September 26, 2019, 10:27:30 pm by KL27x »
 

Online coppercone2

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Re: cryogenic drill bit life extension
« Reply #64 on: October 04, 2019, 10:22:41 pm »


I wonder if parts burnished vs ground would show a difference in a short term acid etch. is there an 'air gap' when the peaks are pushed down between them (so its like deformed) or does it actually bond it. Is it like 'combing' metal, or do the peaks 'weld' to each other?
« Last Edit: October 04, 2019, 10:25:16 pm by coppercone2 »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #65 on: October 04, 2019, 10:48:34 pm »
Quote
is there an 'air gap' when the peaks are pushed down between them (so its like deformed) or does it actually bond it. Is it like 'combing' metal, or do the peaks 'weld' to each other?
As long as it is not overdone, the burnished surface is continuous and connected. If you overburnish (not really possible with a sharpening stone or a grinding wheel), it is possible for a layer of burnished metal to start to separate from the metal underneath. If you flake off the burnished metal, the metal underneath will still have a "fluid layer," you just made the layer so thick and mashed it around so much that some of the excess fatigued and tore away. After it gets so thick, burnishing won't reach the solid metal to turn it into more goo, and you're just mashing the goo until it breaks.

What difference will that make after a short acid etch? Well, the smoother the metal to start, the less variation it will have when it's done, regarding pits and whatnot. Intentional burnishing is usually done to improve corrosion resistance, AFAIK. Well, where it comes to making edges, many people tend to equate bevel shininess with sharpness, so they may intentionally burnish for that reason and/or simply for the esthetics.

Maybe this is related or useful to you in some way. I have mentioned before of not removing ALL the oxides when cleaning off steel things. If it's going to go back to an environment where it will rust, again, just knock off the loose stuff and leave the patina. One of the ways to do that is to use a smooth very slightly convexed and arkansas stone, translucent/black preferred. It will knock off the loose stuff. But if the surface is very smooth, it will leave the patina. If the surface is not very smooth, it will smooth it out. And next time, it will leave the patina. Once the patina is flat and contiguous, the silicon dioxide of the ark stone won't easily scratch through, as long as you use light pressure. This is what I do to my carbon steel kitchen knives when orange spots appear in the patina. The patina is a hard candy layer over a softer M&M.

Of course on large objects, it's much easier to use a wire wheel.

I imagine 500 years ago, burnishing was done by hand to make silver mirrors. And possibly to maintain the patina, natural or otherwise, on steel and iron tools and implements... although it might be a different sense of the word in that context. I've read that in Japan, burnishing was done to swords. After polishing with progressively finer grits, the burnishing was performed by manually rolling hardened steel pins/rods over the metal. This makes the final fine scratch marks disappear. This might sound purely cosmetic, but I bet it was a practical way (at the time) to improve the corrosion resistance of something that took many weeks of labor to make and could have cost more than a house.

« Last Edit: October 05, 2019, 07:36:48 am by KL27x »
 

Offline thesuperiorshave

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Re: cryogenic drill bit life extension
« Reply #66 on: October 05, 2019, 03:36:37 pm »
hi

I just registered to clear up a couple of errors here.  Most of this forum's way beyond my capacitors' capacities, but the convex stone thing, I know well, from taking a knee to those who created it.

First, the German master grinders don't care about our shop 'telling their trade secret'.  It isn't like that to them.  They care deeply about hiding their particulars of heat treat and temper and if I were to post a picture of a sheet of paper with those specifics on it for a batch of razors about to be addressed, they'd have a massive problem (I'd lose the trade partnership, actually).  The grinders' view of me being Convex Johnny Appleseed's more along the lines of "you can tell them, but they won't understand it, and can't achieve it" or something of that approximation.   As a lot, they don't think the North American buyer can come to understand 'the concept's irrefutable superiority' (their words, or more specifically the words [via translation] of the most senior fellow who first explained this to me ~9yrs ago, a man in his 80s who'd been a master grinder for >50yrs). 

I'd taken the stones we've convexed to show them for their blessing, which they gave.  "Have fun, they'll think your crazy, or stupid" was their general reaction.  They're bemused that I'd try to propel the notion.  I would like to point out that getting even a tiny chuckle (or in this case a little smirk at the corner of the mouth) from German engineers is something to be proud of.

Second, there isn't a burr being created when properly convex-honing.  You may confirm this with your e-scope.  This is due to the angles used and the thinness and flexibility of a properly hollow ground straight razor's bevel form.   A burr occurs when one repeatedly rubs one side of a bevel form with a steel cutter with a stone-to-blade angle of approach that is either equal to the incumbent angle dictated by the bevel form (such as when you hone a flat razor flush to a flat stone) or slightly more *obtuse* than the blade's incumbency (such as when you apply tape to the straight razor's spine, and only move on one side of the bevel awhile).   When we take an angle of incidence of stone to blade which is more *acute* than the blade's incumbency (such as when a ground-to-flat razor's bevel's taken to a convex stone), first of all we wouldn't be touching the apex of the cutting edge if the razor's incumbency caused physical obstruction between the spine and the convex hone's acute angle of address; the grinding would start to appear on the rear (closest to spine) side of the bevel form until such time that the physical obstruction was no longer present.  When the obstruction is gone, if a knife's thin enough and of a flexibility sufficient to perform it, it will move from the stone in a way not unlike how you can bring the edge upward with your thumb nail pressure and watch it go back down when you remove your thumb.   

With a properly shaped, tempered, and hollow ground straight razor, you use an angle of address with a convex hone that's extremely close to but slightly more *acute* than the blade's incumbent angle.  The small angle change combined with the thinness and flexibility of the bevel causes the bevel form itself to flex at the very edge for the moment that particular bit of contact's being honed, the terminus of the cutting edge (the grinders call this 'microteeth') gently extruding away and upward from the spine position - and return to incumbent position when its' time on the pass of the honing stroke is complete.  You're trying to impart a slight concave shape to the bevel itself.  All the grinders I've talked to either use a barely convex or flat bevel-setting tool, and then refine on something that's at the limits of what shape the steel will hold. 

Hopefully I did this correct but here is an attachment from a Böker catalog where they confirm that they're using convex stones (how would it be possible to impart a small hollow grind to the edge itself with a flat stone unless you held your spine aside of and within the plane of the flat hone and did some strokes like that?)

I didn't delete any YouTube videos on this topic, and I don't care if everyone makes their own concave plates.  They should.  Nobody's getting rich propelling this notion, if anything it is better to not say it.
 
Knowing what I know now from experience, if I were reading this and wanted to make a quick permanent concave plate for the use with razors, I'd take a ~8x2" hard cheap stone of some sort like a big carborundum, some 60-grit silicon carbide grains and water, and take that to a 12x12" sheet glass at least 6mm thick over and over.   Flatten one side, flatten the other.  You might have to buy two of the cheap stones.  After not too long, you'll start getting a spherical curved pattern cutting in to the glass,...you could also do this with the technique you see here using two sheets of glass  https://youtu.be/P_u9zjamBvs?t=126   but personally I'd rather start with one plate and cheap hones which cost me less to get into my life than a second plate of glass and do not threaten me with laceration.  Keep on with your grinding until your center point is at the very least 0.7mm deeper than the edges and you'll have something that'll work, but if you press on to about 1.25mm it will be better. 
- The plate's curve intensity should be more curved than the least straight razor's deviation from true, such that the hone-to-be cannot touch the razor edge twice w/ a gap in contact.
- The plate's curved intensity should not be so intense as to cause the razor's edge to be unstable.
- What exactly is the best position would depend upon the uniformity of the production values and metallurgical structure of the razor at hand. 

As I've found even granite tiles do start to increase their sagitta if used flush to whetstone with grit (originally I did this with two granite tiles and that took an astoundingly long time), I'd only recommend using with silicon carbide sandpaper affixed to your tile, with some grit sprinkled on the surface at least as fine as the backing paper.  I use hairspray just a spritz or two to the backside of the paper, then use up a whole paper's lifespan all at once with grinding, it removes easily and any residual tackiness can be easily washed with soap and water.   A pair of cheap but reasonably flush to one another tiles from Lowe's cost me $6 and I got the top one to >1mm deep in about 2hrs of labor, that I'd only have to do once as the sandpaper fronting it keeps the shape in place. 
 
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Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #67 on: October 05, 2019, 09:32:04 pm »
I dunno how you found this thread, but thanks Jared/Jarrod for taking the time to join the forum just to clarify. I hope I didn't misrepresent what you put out there too badly.

Quote
"you can tell them, but they won't understand it, and can't achieve it" or something of that approximation.   As a lot, they don't think the North American buyer can come to understand 'the concept's irrefutable superiority'

"Have fun, they'll think your crazy, or stupid" was their general reaction.
Bingo. This is exactly what I feel, but is it really just NA? I wonder if it's any different to average Germans, these days.

This why in one of my posts I lamented the fact that after we die, some kid is going to acquire your excellent stones and go on the internet to figure out how to flatten them. And on the (english speaking) internet, they will encounter exactly nothing to dissuade them from their purpose! Except for a few YT videos from a lone guy who does it for the pure passion of sharing this insanely better way, even though there's basically no money in it. (That would be you!) Everything else on the modern english speaking internet is just "dish = bad. Flat = good. Flatter = gooder. Let me show you how to flatten your stone."

And it wasn't always like this. I remember a webpage showing and describing the benefits of curving an arkansas stone in very good detail. I also remember a webpage showing how you can (actually) flatten two stones against each other without making one concave and the other convex. That was probably over a decade ago, though. Our modern internet is more like a popularity contest. The most popular view is correct. And I think there is also some influence from $$$. There's huge money in making people forget how to do things and then selling them a solution with a high profit margin that you import from Asia and sell at many times the cost. Lots of money leftover for marketing and salemen. In any online discussion about sharpness, any real discussion is discouraged. There is always way too many peeps talking Naniwa 6000 GTX vs Shapton 8000 GSXR-7 Pro. And I'm sure many of them are real folks, but I bet there was plenty of help getting this situation created in the first place by internet/social media marketing teams. I remember 10 years ago, there was a couple year period where in every discussion there were multiple guys interjecting any discussion just to say how amazing the Worksharp is, and only $XX.99... And again, I think many were real people, but I think there were a lot of marketers pushing it at that time.  Do you think a video showing someone sharpen a cheap knife on $1000 (retail) of waterstones gets 7 million views naturally? I doubt it. But other aspiring Youtubers will see that and copy it. And they might even get a bump in views from marketing bots, if their video promotes someone's agenda well enough.

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Second, there isn't a burr being created when properly convex-honing.
You know, I have never been able to feel a burr after sharpening my razor on the convexed ark stone. I just always assumed it there but too small to feel. I will take it from the guy looking through an electron microscope, though.

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- The plate's curve intensity should be more curved than the least straight razor's deviation from true, such that the hone-to-be cannot touch the razor edge twice w/ a gap in contact.
- The plate's curved intensity should not be so intense as to cause the razor's edge to be unstable.
- What exactly is the best position would depend upon the uniformity of the production values and metallurgical structure of the razor at hand.
Interesting, the kind of details what can eventually be noticed by a company/culture that has done this for centuries. I imagine it started out as "oh it works better when it's sorta rounded." And 200 years later, this.
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All the grinders I've talked to either use a barely convex or flat bevel-setting tool, and then refine on something that's at the limits of what shape the steel will hold.
Interesting, but I'm not sure if you are reading too much into this. For one, IME, hard (non-slurry) stones just don't work well in coarse grits. The stone gets dull, and then it just sucks (exception being diamond plates).*** The coarser the grit, the more friable it needs to be, and the more friable, the more it just doesn't work unless the blade fits to the stone to get enough surface area of contact to get liftoff. Finer grits is where the hard/dry convex stone really shines.

***I have found the coarse side of many stones to be very firm and very coarse. This includes a very cheap silicon carbide stone I have, as well as the Norton Combo India, for examples. And I have found this side of the stone most useful for shaping (including flattening) other stones. Do they cut steel? The first doesn't do it so much as just make crunchy noises whilst giving the feeling of dragging a steel part over gravel. The Norton cuts steel ok on the coarse side, but it can rattle your teeth, and it's almost slower than just using the fine side and getting a better finish and/or edge. But rather than be disappointed with the performance, I found that what is too dull for cutting steel is still fine for shaping of other sharpening stones, and maybe that is what some of these "coarse sides" were designed to do from the start. The larger chunks of firmly bonded abrasive can chip apart the other stone without taking as much wear, themselves. Grind wheel dressing stones come in even coarser grits in a very hard, firmly bonded stone, too. But the surface speed and inertia of grind wheels and the way you use them (better hold on somehwat firmly, at least, to your part) means everything is coarser and still works out fine.

Another way you might think about it, the fundamental reason for curving the fine stone (I think) is to reduce surface area of contact (aside from razor-specifics). And the coarser stone has way less points of contact per unit surface area. So even a gentle curve might be overdoing it, leaving too few points of contact and not being able to do what it's supposed to. When curved it would be like, say, putting 3 points of contact against a spot on the bevel and gouging it. The teeth could sink too deep and get stuck. It would be grabby and ineffectual. The law of averages is working with a much smaller sample, and your blade would be hitting higher points and banging up the edge and just bouncing around.

Analogy would be sanding a large flat area of wood, you would need to use a really coarse grit. But if you wanted to sand a very small flat spot, you would start with a much finer grit. If you try to sand the end of a toothpick on 36 grit, it won't be rougher but faster. It would be rougher, yeah, but it might not even do what you want it to. Instead of cutting away material, you would just splinter the toothpick and break it.

Even here, in our backwards country, ceramic rods are way more popular than flat ceramic sharpening stones, and we don't have super coarse rod sharpeners. I wonder if for every sale of a fine ceramic flat stone, there is a German engineer smirking, thinking it's the perfect tool for rounding over the point of a needle.

Edit2: there are multiple reasons this info is never going to take root in the modern US. One of them is many of us can't even tell what is flat. Seen a guy take a brand new King waterstone and "flatten it" to improve it, right out of the box using sandpaper over a piece of glass. For one, King waterstones are flat, out of the box. But more importantly, even most waterstones are too hard to flatten like this over that large of a surface area (7"x3"ish). What you will end up with once the scratches end up reaching the center is a convexed surface. A straight edge will easily verify this. Coppercone2 experienced this when attempting to flatten a 3x3" aluminum surface with a file. The result is a convex surface. Many people believe this just a result of imperfect biomechanics, but the file just can't cut that much surface area at once.    So if an average person can take a flat object, make it curved, and then call that "flattening," it's a steep curve from there.
« Last Edit: October 07, 2019, 05:36:41 am by KL27x »
 

Offline KL27x

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Re: cryogenic drill bit life extension
« Reply #68 on: October 05, 2019, 09:59:16 pm »
Oh, and...

Jarrod, if you do read this:
Can I suggest to you two words? Sintered ruby.

Apparently, this stuff was discovered/created by a German company some 30 years ago. The patent expired in 2013, best I can tell. So now it is pretty much dirty cheap. Much cheaper than translucent arkansas stones.

The fine sintered ruby is maybe even finer than translucent arkansas. And after it is gently convexed (diamond plates; no sandpaper, here!) it leaves a most excellent razor edge, IMO. It seems to cut a bit more efficiently with less burnishing.

What I have found, and it might be wrong, is that sintered ruby is made the same way as white ceramic crock sticks, except a bit of chromium oxide particles is added to the aluminum oxide particles before sintering. The end result is it cuts better than white ceramic (IMO), and it is also 30-40% tougher. I have dropped a new 6" long, skinny machinist stone onto concrete and cringed. But the thing bounced and rang like a bar of steel, and where the sharp corner hit the concrete was some concrete dust... but the corner wasn't even fractured. I tend to sharpen razors on regular ark and then finish with the sintered ruby, leaving out the translucent ark, these days.
 


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