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?