by Doug Coulter » Mon Dec 12, 2011 9:14 am
I've found the diamond hole saws about a zillion times better than the diamond coated rods with flat ends - that middle doesn't cut well. I always use a pretty slow speed - easy to burn the diamonds off. I often make a little dam around where I want my hole of modeling clay to hold the water, which seems to work the best on this hard/brittle stuff compared to other cutting/coolant fluids - you retain the abrasive slurry at the cut the best that way. I set the drill press for a couple hundred rpm tops, put a constant but low down force on the quill (eg tie a weight to the handle, or just the weight of my arm), and wait. I do this the same for glass, quartz, alumina (the last being the hardest) but I suspect this would be the plan for ferrites as well. Waxing a piece of glass or similar to the backside before starting helps with chipping as the drill gets through (and you don't lose your water/slurry until it doesn't matter anymore).
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.