1. ## Adjusting belts for r.p.m.'s

A friend of mine gave me an old Heavy Duty Complex drilling & Milling Machine. On the front it had the combination of the 4 belts for your r.p.m.'s of where to place them on the pulleys but it's all wore out. I tried going to the co.'s website but to no avail. Can anyone help me out or give me a website of the formula ?

2. I just took a quick look in Machinery Handbook. The key is to find the pitch diameter or effective diameter of each pulley. One page showed it as about 1/3 of the belt thickness smaller than the radius of the pulley. if you need more accurate, the exact formula is in there someplace.

Lets say one of your pulleys has an O.D. of 4" or 2" radius. And the belt you have is 1/2" thick. So, subtract 2" - (1/2*1/3) = 1.833 effective radius. Times 2 for effective diameter.

Get the effective diameter of each pulley. The speeds you get will just be the ratios of the two pulleys effective diameter times the input motor speed. For example if you have a 1700 RPM motor on a 2" effective diameter pulley driving a 4" effective diameter shaft:
1700*2/4= 850 RPM

Do this for each combo and make your table.