Wednesday, March 25, 2015

Machining Ultra Hard Materials - II

I missed something that I should have said last night

Grinding hard alloys is not new, and not limited to the lapidary equipment I mentioned last night.  Surface grinding machines have been around for ages, and that's just the start.  There are centerless grinders, cylindrical grinders, and more, to emphasize that grinding is an acceptable technique.  I steered away from those big tools because I just don't know of any hobby or small shop-sized grinders aside from a bench grinder or a hand held grinder.   

It turns out, I didn't double check.  Grizzly has a small (-ish) surface grinder at a price that falls in line with a lot of other home shop tools.  That probably means other people have them, too.  Griz doesn't have centerless or cylindrical grinders.  I don't think a surface grinder could do something like that bearing I was talking about. 

When I wanted to cut titanium on my Sherline milling machine, one of the retired machinists who uses one commented that I should grind it rather than machine it on the little milling machine.  Titanium is quite a bit more machinable than ceramics or superalloys; it handles quite a lot like stainless steel.  Still, this old machinist thought I'd be better off grinding than cutting.  I had no real trouble cutting it. 

I suppose I come at this from thinking of ceramics and other hard, brittle materials as being more like rocks and crystals, and grinding is the way to cut those.  There are millions of faceted stones on the market, including extremely hard ones like sapphire, rubies, and diamonds.  Every one of them was ground.  Despite the image we all have of the diamonds being cleaved with a hammer, probably from commercials, diamonds are "cut" by grinding the facets into them like every other type of stone.  Cleaving is only done on large, valuable stones, to make smaller, valuable stones out of them, which are then ground away to shape.   
A CNC lathe carving an ornamental angel in stone. Chances are, this is a softer stone like alabaster that can be cut with conventional steel or carbide cutters.


  1. SiG

    We use a DedTrue fixture, on a surface grinder, to neck down carbide tools to custom specs; here at the Mill.
    I imagine you could pick one up reasonable at a machine wholesaler.

    Whitehall, NY