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View Full Version : Grinder RPM and CBN Wheels?



Joe Beaulieu
12-24-2015, 5:04 PM
Hi Folks,

First - Merry Christmas - I hope all you galoots have a great holiday with your family and its a very nice Christmas!

I have a question about grinder speeds. Many tools and grinder wheels recommend "slow speed" or "low speed" grinding operations. I have a variable speed Delta grinder. It is a very common and recognizable tool. It is spec'd that the range of rpm is 2000 - 3000. Does 2000 qualify as a slow speed? I have seen the range posted in places as 1600-3200, with the understanding that the "slow" speed is 1600. Are these speeds generalizations? Does it mean my grinder at 2000 would still be within accepted range as a low speed grinder? I think you get my drift...

I am considering grabbing a CBN wheel and using it to set the camber on my plane blades. Is this an acceptable way to achieve this? The wheel is expensive, so I only want to get it if it is going to minimize my sharpening time. I spend way too much time with new blades trying to get cambers with a honing guide (Lee Nielsen) and Shapton stones. I start on a 325 grit Shapton and use the counting strokes on each side method while applying pressure on opposing edges of the stone. This is after I have gotten the bevel to where I think it should be. At this point I have already done the back through the entire range of stones and it is mirror and flat. I have great success with planing using blades that come "pre-cambered" in used planes. However on my new blades I cannot seem to get the same arc. I realize the opposing pressure method won't make the camber particularly visible without using a straight edge. I am pretty frustrated using the stones. Its a ton of time and the results are pretty unsatisfactory. I am very interested in the CBN wheel as a solution.

I would appreciate any help any of you folks with more experience would care to lend. I feel this is my last sharpening "hurdle" and I want to fix this asap.

Thanks again all.

Joe

Tom M King
12-24-2015, 5:51 PM
327856I ordered a couple of different slow speed grinders, and couldn't find one smooth enough for me, so I tried a regular speed Metabo. Metabo didn't make a slow speed one when I was looking. The CBN wheel works fine on a regular speed grinder. I used some beater chisels to see what it took to overheat one, and it took a lot of pressure. I'm not recommending it for anyone else, but it's working fine for me. I've been using it for at least a couple of years, and haven't blued a corner yet.

John K Jordan
12-24-2015, 6:56 PM
My experience is a 240 grit CBN wheel cuts cooler than the standard wheel I took off the same grinder, at least with sharpening my HSS lathe tools. I don't know why - maybe it's because the grit particles are more widely spaced or maybe they don't get loaded up with fine steel particles.

BTW, I bought the same Metabo for my little weld/farm maintenance shop and use it with a coarse wheel and a wire brush. Man, what a grinder! With the wire brush it's easy to tell it has so much more power than the previous two pieces of junk that happened to be named grinder.

JKJ