Jade

[scottsss]

I'm interested in profiling some jade. My experience is with metals and plastics...What would be a good source for diamond tooling and speeds and feeds thanks.

[RomanLini]

I've worked talc and jade by hand with a file and a hacksaw, they are quite soft.

I'd skip the diamond tooling and just try carbide for a start. Considering how easy it cuts with a file or saw I can't see speeds and feeds being that critical. Just go slowish and take real fine cuts, your biggest problem will probably be the jade breaking as it is very brittle and you don't want to put much force against any part of it. Especially since it is common to have fine fault lines through the piece.

[scottsss]

Would it help at all if I cast something around the jade to give it more support...So make my outside shape then place it in wax or some other material to prevent cracking....I was looking maybe at black jade to play with.

[RomanLini]

I think you will just have to try some things and see what works.

If you hold it rigidly and take fine cuts it should be ok.

[scottsss]

I'm use to metal and plastics....For fine would 1/3 the dia of the cutter for depth and a ruff chip load of .001 to .0005 be a good base to star from?

[RomanLini]

Ouch! Try a fraction of that. Fine cuts.

[awerby]

Jade is another story altogether. I'm not sure what Roman was working on with his file and hacksaw, but it doesn't sound like true jade; probably it was a green steatite, which can look rather jadelike. Jade is also the least brittle mineral I can think of, due to its fibrous structure. Of course, if the material is fractured, that will cause it to fall apart at the cracks, but that's not the same as brittleness.

That black nephrite is not going to respond well to attempts to cut it with a carbide endmill, no matter how slowly you go. While the tungsten carbide cutter is significantly harder than the jade (9.0 vs 6.5 on the Mohs scale), the toughness of nephrite, from the interlocking fibers of actinolite that permeate it, is not going to allow any chips to peel off. All you'll do is rub the teeth off your cutter and heat up your jade.

You will need diamond tooling to make any significant impact on that material. Sintered diamond burs will last a lot longer than plated diamond ones; once the plating wears off, cutting action ceases, but in a sintered tool there's diamond underneath, not just on the surface. You'll also need flood coolant to flush the cut and keep the tool from overheating. Make sure your mill's slides and screws are well-protected from the abrasive slurry that's produced, or this will kill your machine in short order.

Here's a source for the diamond tooling you'll need (go with the 60 grit for roughing out, and hit it with the other grits successively to refine the surface before polishing):

http://www.mtmist.org/products/jade_eater.html

I'm not sure what feeds and speeds to use, but start with a very light cut (like .002" depth) at a moderate feedrate and see how it goes. "Chip load" calculations don't apply here, since this is a grinding, not a cutting operation.

Andrew Werby
www.unitedartworks.com