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Originally Posted by Connor
In all honesty, I purchased the Leeson motor many years ago with a 3450 RPM after taking the advice of a Canadian knife maker I used to e-mail daily. His advise was that it was always better to have it and not need it, rather than need it and not have it...
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In the case of a knife grinding motor, that's only true if the setup allows for variable speed.
More specifically, it needs to allow for much slower speeds.
You may be able to use a 3 or 4 step pulley based on your motors shaft length, but you're still gonna be running pretty fast at your slowest speed when using your average pulleys.
IIRC, the average belt speeds on your typical knife grinders are calculated using a 1750 RPM motor (give or take 50 RPM). On a 2"/3"/4" step pulley, I believe this will yield somewhere close to the following belt speeds:
3500 ft/min
1750 ft/min
800 ft/min
With a 3450 RPM motor, you are essentially doubling those figures, so that your lowest speed will be around 1600-1750 RPM, and your highest speed will be closer to 7000 RPM, which is pretty fast for a grinding belt (or contact wheels and bearings) to be moving.
You may want to make sure that your belts, wheels, and bearings can withstand these speeds and the resulting tempuratures, as this will heat things up a lot faster. Also, any vibration will be ampified, and parts could be quickly compromised.
You need to also consider that detail work which requires slower belt speeds will be a lot more difficult, if not impossible to do with 3450 RPM.
Ideally, one would have a VFD which adjusted between 0 FPS and 3500+ FPS. In this case, I can see why it wouldn't hurt to have more power and not need it, although you would still need to keep in mind the tolerances of your grinder parts, and the added dangers/difficulties that higher belt speeds can impose.
Just my $.02. Others may agree or disagree.
All that being said, that grinder looks like it's coming along superbly, and I can't wait to see the finished product! Lookin' good!