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Die cast step pulleys - danger of failing

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Quite a few people, including me, are running die cast zinc conical step pulleys as a cheap alternative to a VFD on our grinders.

I had checked the pulleys for runout before running them, and they were good enough, within a few thousandths. After running them for a few months, the runout and vibration is extreme. They will soon crack if they haven't already and probably fly off at high rpm. 

Note that these zinc alloy pulleys are made for fractional horsepower only:


I don't have a good source for high quality heavy duty steel step pulleys, unless I turn them myself on the lathe. Which I may do or just wire up a proper VFD. The other benefit to having a motor controller is soft start and braking. My 3HP grinder motor cranks up to 3450 RPM instantly, putting a lot of stress on the weaker components like the belt and pulleys. 

So, be careful not to use fractional HP rated pulleys on your KMGs and the like.


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