lathe speeds?

[Wally Wenzel]

Hi all, I know there is a simple way to figure shaft speeds knowing motor speed and pully size but for the life of me i can't come up with it now. Doe's any one remember how it is done, thanks wally

[Jim Davenport]

Here's an example, I found on another site:
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1. <LI style="FONT-WEIGHT: bold; MARGIN-LEFT: -10px">Divide the diameter of the driving (or motor) pulley step by the corresponding step size of the pulley mounted on the drill press spindle:
   2 ÷ 5 = 0.4
   3 ÷ 4 = 0.75
   4 ÷ 3 = 1.33
   5 ÷ 2 = 2.5
2. Then, multiply the motor speed by the results of the above calculation to get the approximate spindle speed at each pulley step:
   1725 x 0.4 = 690 rpm
   1725 x 0.75 = 1293.75 rpm
   1725 x 1.33 = 2294.25 rpm
   1725 x 2.5 = 4312.5 rpm

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[Brett Baldwin]

Jim, the example you chose has the math right but the wording is wrong.

Wrong wording:
Divide the diameter of the driving (or motor) pulley step by the corresponding step size of the pulley mounted on the drill press spindle:

Correct wording (changed to be more universally applicable):

Divide the diameter of the driven (lathe spindle) pulley by the diameter of the drive (motor) pulley and multiply by the motor RPM.

Driven/drive x motor RPM = spindle speed

So the math in Jim's post is correct but the wording was not. Hope that refreshes your memory Wally.

[Tony Sizemore]

Here is something you may find helpfull...
http://www.csgnetwork.com/pulleybeltcalc.html