It's my understanding that if it's inert, there's no danger. It's when chromium is in a gaseous state that it becomes a hazard.
Hex Chrome is an IARC-1 carcenogen, and 8 out of 100 people exposed to it develop lung cancer.
http://www.epa.gov/iris/subst/0144.htm http://www.osha.gov/SLTC/hexavalentc...tory_text.html
While chances of exposure when machining are less than welding and cutting, there's still that chance.
Speaking of gypsum, that's part of the reason I do what I do for a living now. I was a plasterer for 20+ years and was exposed to all kinds of airborne crap on a daily basis, including gypsum dust and free silica, as well as asbestos on certain occations.
I'd rather be safe than sorry is all I'm saying... the only real way to find out if exposure is occuring is to test for chrome hex levels in the area where potential exposure from materials is happening. If concentrations are less than 2.5 micrograms per cubic meter, you're golden. If more than 2.5, regular testing is suggested, and more than .5 micrograms per cubic meter, toxic exposure is happening and corrective actions need to be taken.