by Chuck St. Louis
After reading a couple of very interesting articles in this magazine on how to balance grinding wheels, I thought it might be of use to mention a few things that have worked for me.
Why is it so critical to balance a spinning wheel? A typical grinding wheel 6″ in diameter turning at 3400 rpm will have a pull, called centripetal force, of 970 Gs at its rim. (Let’s round that off to 1000 for argument’s sake.) I know it hard to believe, but almost 1000 times the force of gravity will be exerted at the rim of the wheel. If a grinding wheel were to have one gram (.035 of an ounce) at its rim out of balance at 3400 rpm, that gram turns into 1000 grams (35 ounces) out of balance shaking force. It’s no wonder an out-of-balance grinding wheel can literally make your work bench walk! Gravity also acts to compound the problem every time the heavy section of the wheel passes the bottom of its rotational path. Better to balance the wheel once!
The first thing I do when I’m about to use a new grinding wheel is give it a slight blow with a small hammer to make sure it rings. If it makes a thud sound, beware of cracks. Very often, grinding wheels come with an oversized hole. To sell the grinding wheel so that one-size-hole-fits-all, a set of plastic bushings are normally provided to make up the difference between the larger hole in the grinding wheel and the smaller diameter of the shaft on the grinder. If your grinding wheel has a hole smaller than needed, it can be drilled out oversize with a masonry drill bit in the drill press. Why would you want an oversize hole? Read on! (To be continued…)
“Balance Your Wheel Once” appears in the May/June 2009 issue of The Home Shop Machinist. If you are a subscriber, stay tuned! The issue will be in the mail soon!
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