Variable Speed Bench Grinder

[tom lucas]

No, that is not so. Sorry Tom. The carbon steels thrive on CBN (I have done this for years). The steel that should not be ground on CBN is mild steel or unhardened steel.

As far as I am aware, mower blade steel is water hardened, in other words, generally W1 steel. That is perfectly doable on CBN ... as long as it is hardened enough. The worst case scenario is to clean the CBN wheel by grinding with a hardened steel.

Regards from Perth

Derek

I've read it several different places. Perhaps their is confusion regarding what types can or cannot be done; I don't know. As usual, there is contradicting info on this. My experience with my mower blades tell me not to do it again. It left it clogged up a bit until I sharpened several 10V steel tools on it. Because I have a high speed AO grinder, I don't chance it. Mower blades just aren't worth it.

[H. Gregory Porter]

?..

... Because I have a high speed AO grinder, I don't chance it. Mower blades just aren't worth it.

i got clarification on this. You can use CBN for softer steels if and only if you slow the grinder speed/feed rate and go slow enough to prevent overheating. Those putting CBN on fixed speed ac grinders have to be meticulously slow when sharpening softer steels to prevent heated metal from loading up the grinding wheel.

I’m going with the variable speed grinder, so My plan is to try sharpening the lawn mower blades at the lower wheel speeds, increasing it until I can begin to feel warmth near the cutting edge.

[tom lucas]

Jon, Thanks for the education. I knew VFD’s provided speed control. I did not remember it would convert 3 phase to single phase.

I thought was the other way around: single phase to 3 phase.

[H. Gregory Porter]

You’re correct. Must have Had a dyslexic moment — of a sort.

[Chris Fournier]

My thinking and practice is that the wheel grit and bond are far more important than the machine speed. I have no need for a variable speed grinder but I have spent hours getting my grinding skills up to snuff. And I'm still better some days than others...

If you want to discuss the importance of speed it should be with regards to your feed speed of the tooling. I've found this to be key on bench, cup, surface and cylindrical grinding jobs.

[H. Gregory Porter]

I received my 180 grit CBN wheel. I tested it on my lawn mower blades. The Mfgr said it was ok to grind softer steels - ie non HSS blades, as long as I ground at slow enough speed to not generate heat. The sifted hot steel would clog the CBN wheel. I placed my fingers about 1/2 to 3/4 inch behind the grinding surface and only for a brief few seconds even felt any warmth while grinding 6 blades. I ground the first 5 blades at about 1000rpm on an 8”wheel. I increased the speed to about 1400 rpm for the last blade. It was on this blade at a slower feed rate that I felt just a tinge of warmth near the cutting edge.

Although this seems adequate for lawn mower blade grinding, I would not use this if I were in the business of sharpening mower blades. When I completed 6 blades, the wheel looked every bit as new as when I received it. There was no evidence of clogging just as the mfgr stated. For the 1 or perhaps 2 times per month that I would sharpen a mower blade, I have no reservation of using the same CBN wheel that I would use on my finer plane and chisel blades.