Author Topic: 1/8 inch shaft silicon carbide cup wheel?  (Read 724 times)

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Online coppercone2

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1/8 inch shaft silicon carbide cup wheel?
« on: May 14, 2021, 03:02:11 am »
So I am having good results with copper on my proxxon mf-70 mill, and when I bought it the guy threw in a bunch of cup wheels made out of something, so I always wondered if I can get it working as some kind of surface grinder/surface improver.

I did one small side of a copper block with it after sanding it on a belt sander to some attempt at flatness and it seemingly worked, but while doing it I had some chips and great difficulty at depth adjustment to get 'grinding passes'.

I rubbed it on a surface plate afterwards and it looked OK, slightly bowed in the middle, but it got rid of the scratches and did not wobble on the plate or have terrible high spots like the other side (whatever I did before the little 'grinding' operation made it have a mountain range in the middle).

However when I proceeded to use this stone, it started like. barking/knocking and acting terrible, gouging, changing depth in the collet, etc. I assume this has something to do with tool life, and that maybe the cup wheel I had was not compatible with nonferrous grinding. I used oil as lubricant from a drip.

I thought maybe this surface finishing process would have some merit if I could get mini cup wheels that have appropriate abrasives, i.e. silicon carbide, or cubic boron nitride. I have that mini expensive cutting wheel for the dremel which claims is CBN coated (not diamond), and it works pretty amazing. When doing deburring I also find that the green silicon carbide is good at deburring weird stuff, it does not clog.

DO such cup wheels exist? I thought to just get random 'points' made of silicon carbide, but I wonder if there is like a precise one optimized for this kind of thing?


More specifically, how important is the cup shape on the bottom. What if I found the right material but its totally flat on the bottom, like an abrasive cylinder for a jig borer, is that compatible with surface finishing by linear passes?
« Last Edit: May 14, 2021, 03:14:46 am by coppercone2 »
 

Online coppercone2

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Re: 1/8 inch shaft silicon carbide cup wheel?
« Reply #1 on: May 14, 2021, 05:51:45 am »
I bought normal silicon carbide points, I can use a diamond point to grind cups into them if they give me a problem.

I think what was happening is the stone was clogging, causing way too much friction and stalling abruptly. The technique is worthwhile because while the end-mill makes it flat enough, if I run my fingernail across it I feel the ridges, but after the stone grinding its just as flat or flatter but feels pretty smooth, and is at a roughness level where I feel like I can transition to sand paper or other manual abrasives without disturbing the geometry. Since its a non ferrous metal I think SiC can help.
 

Offline bill_c

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Re: 1/8 inch shaft silicon carbide cup wheel?
« Reply #2 on: May 15, 2021, 03:33:37 am »
Surface speed is diameter x RPM, which gives zero surface speed at the center, which means no cutting/grinding at the center. Cup shape shouldn't much matter if its even and it doesn't reduce mechanical strength, but removing too much of the center gives you less working area and higher surface pressure which may cause wheel to wear too fast. A starting point would be removing the center 1/3 or maybe as much as 1/2.
 

Online coppercone2

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Re: 1/8 inch shaft silicon carbide cup wheel?
« Reply #3 on: May 15, 2021, 05:08:42 am »
so the friction will kill it unless I figure out how to bowl out the center?

I have a few diamond points from a surface grinder wheel flatener, they are old, I use them very rarely to true a bench wheel, but I have been meaning to get the real bench grinder truing diamond hand held thing.

Do you know how long they will last making these bowl shapes in silicon carbide?

I assume there is no cheap way to do this, i.e. how do you hog abrasive stones? Do those really cheap chinese diamond burrs stand a chance at being 1:1 trade offs with carbide stones to make bowls? I thought to buy them but it seems like a real waste of money, the more I think about it the more it seems like this idea is a bogus ass money pit


and given the small geometry and stuff, what do you think a reasonable depth of cut is for silicon carbide surface smoothing experiments? Like, I was getting truely awful scared for my machine noises that seemed to be cutting OK and noises that sounded like it was going OK but the machine was periodically like.. exploding? bumping? knocking? thought something was gonna blow up

I don't think its anything to do with the machine, because I removed lots of metal today just fine with a real 3 flute carbide end mill meant for non ferrous metal (atlas cutting tool company ), I assume just trying to use stones on it = my settings are totally fubar..

If I acutally did try to study the literature if it exists on cup shaped grinding with such a size reduction, do you think there are any non obvious pitfalls related to such drastic down scaling?

I.e. I would start to do RPM calculations, when I find them, from 0.002 depth of cut. Is this a reasonable starting point still? I am worried its non viable and I am wasting time doing the unachievable/unstable.
« Last Edit: May 15, 2021, 05:19:13 am by coppercone2 »
 

Offline bill_c

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Re: 1/8 inch shaft silicon carbide cup wheel?
« Reply #4 on: May 15, 2021, 07:09:45 am »
I have used those cheap diamond burrs on solid carbide many times, just don't use excessive force. Heat is another problem.  The grinding wheel and the surface that you are trying to grind, both expand as the temperature increase, which causes more heat. I'm thinking this may be mainly why it did so poorly when you tried it.  Copper is rather soft and gummy, I would use really sharp high speed steel tooling and lube (kerosene or light oil) works very well.
 

Online coppercone2

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Re: 1/8 inch shaft silicon carbide cup wheel?
« Reply #5 on: May 15, 2021, 08:04:18 am »
dressing the silicon carbide with a single diamond point might be a good way to get it really sharp? or does that make it really not sharp?

temperature makes sense because as it was cutting its slowly expanding till it expands too much abruptly stops, fractures and keeps going. when i looked at the edge of the stone it was chipped

this is tellurium copper so its a bit better but I heard many people say that its their least favorite thing to machine, and one incident of someone almost getting hit by a object.


still thinking back to trying to make a cube with a file and a sander 2 years ago and this has to be worth it lol, don't think those fond memories will leave me for the rest of my life
« Last Edit: May 15, 2021, 08:10:01 am by coppercone2 »
 


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