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Will42805

Newby 2x72in. belt grinder

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Im thinking that maybe i should gust go with a vfd, 3 phase, direct drive, 1700 rpm motor till i can afford a 3600rpm one with an 8 inch wheel. Ive never been the start out small and continuously upgrade sort of person. Better to just save up and do it right.

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Will,

If you are using a VFD, speed adjustment will be accomplished electrically.  If you wanted higher speed, you'd increase the frequency to your motor.

Most people use speed controls on belt grinders to slow them down.  It doesn't get mentioned very much, but fine grit abrasives have much higher surface contact than coarse ones.  This means that with equal speeds and feeds, fine grits have more friction which generates heat.

I have a fixed speed belt grinder that's frankly, way too fast for fine grits.  A few seconds of contact would easily draw temper colors with my finest belts.

If it were me, I wouldn't add anything to your grinders drivetrain that increases speed, vibration, or work for your motor.

 

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A 15 tooth sprocket in the drive train will induce a sinusoidal speed variation in that train of 2.19%.  So...whatever speed you are trying to run at will actually be varying by 2.19% with each sprocket tooth.

The reason I bring that up is sometimes 2% can be significant enough to feel and cause vibrations in machinery...sometimes not.  ALL chain drives will do this, the smaller the sprocket tooth  count, the greater the effect.  People in my business have this nasty habit of wanting 6 tooth sprockets (I use mostly 6" pitch chain so the notion of 6 tooth isn't whacky) which introduce 13.4% speed variation with each tooth engagement.

Oh..chain size.  Note that the HP ratings in the books are for PERFECT situations..no misalignment or uneven loading, smooth energy transfer, perfect lubrication, etc.  Go bigger.  IIRc you mentioned # 35 and that's too small, even if the book says otherwise.  

I'd skip the roller chain on a belt grinder anyway.  There are better choices for that situation.

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