What Woodturners Need to Know about CBN
November 16, 2019
What Woodturners Need to Know about CBN (Cubic Boron Nitride)
CBN wheels will even sharpen pure carbide bits and tools, although the life of the wheel will be compromised enough to probably not make it economically worthwhile. A wet CBN cutoff wheel will slice through carbide at the same speed as a diamond wheel, it just wears faster. Diamond is still the best abrasive for cutting pure carbide.
If you are a fan of the newer powdered-metal woodturning tools (I know I am!) a CBN wheel is a must. My first Crown Bowl Gouge of powdered-metal design seemed scarcely worth $5.00 extra UNTIL I bought my first CBN wheel! Wow, those sharpened microcrystalline carbides really do perform better than did the dulled or removed ones when the tool was sharpened on an aluminum-oxide wheel.
Everyone talks about having to buy a slow speed grinder to successfully use CBN wheels. I say it just ain't so; that is, if you're willing to be less aggressive with your grinding. I read up on industrial abrasives for cutting metal, and CBN is superior to all others at very high speeds, and also at higher temperatures, so speed (and attendant heat) is not deleterious to these wheels. I contacted Cindy Drozda, who sells fine CBN wheels, and she says she uses her wheels on highspeed grinders. I also contacted some other vendors and got the same report. The big issue seems to be that the CBN wheels CUT SO MUCH FASTER at the higher speeds; so for neophyte sharpeners it has been recommended to go with slow-speed grinders in order to extend their tool life. Well, if you can slow down your aggressions, and grind a bit more gently, you can save yourself the price of a slow-speed grinder. I've had no problems with CBN wheels at 3600 rpm. They cut beautifully, and the grind is superb.
Ohh, you shouldn't throw away your old aluminum-oxide or silicon-carbide wheels. You'll still need them if you do any grinding of mild steel. CBN is for HSS only, not for mild steel. Don't forget this, lest you have to buy yourself a new CBN wheel. I keep one CBN wheel on one arbor of my grinder and an aluminum-oxide wheel on the other arbor of the same grinder, and it works out fine for me.
The Arizona Woodturners Association does occasional group buys of CBN wheels, and we get a nice discount, which we pass on to our members who participate in the buy. If dull tools is one of the banes of your turning -- like sanding is for me -- you can cure the problem with the purchase of a CBN wheel.
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