cryogenic drill bit life extension

[eKretz]

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...

[KL27x]

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. 

*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.

[SparkyFX]

Whatever you call it, it will probably be gone after drilling the first hole. Thats what the drill is made for.

[KL27x]

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.

[eKretz]

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.

[coppercone2]

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.

[coppercone2]

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.

[KL27x]

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.

[coppercone2]

safety #1

[KL27x]

Don't tell me the guy with an oxy-acetylene torch in his garage is afraid to use a knife?

[coppercone2]

they call me mister hook

[SparkyFX]

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?

[KL27x]

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.

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.

[coppercone2]

do all materials bur/burnish? or at least, all metals of all hardness?

does it happen on some level with oxides?

[KL27x]

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.

does it happen on some level with oxides?

I don't know, but i'd take the under on that.

[coppercone2]

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.

[eKretz]

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.

[SparkyFX]

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.

[KL27x]

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.

[KL27x]

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.

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.

[eKretz]

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!

[KL27x]

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.

[eKretz]

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.

[KL27x]

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."

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.

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.

[coppercone2]

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?