# Thread: Calculate multi pulley/spindle speed...how?

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## Calculate multi pulley/spindle speed...how?

My mill is a US Burke V2. Has the original spindle pulley (6 step) but the drive pulley (4 step) is not OEM, I don't really know if the motor is original spec. I was looking into the VFD route but came across a set of 5 step pulleys. My plan is to run a setup like a drill press using the 3 pulleys. The spindle pulley is 8"-3", the 5 step pulleys are 2"-6". The motor turns 1740 RPM's. I have 1 of those cheepo laser RpM finder outers but would like to try to figure out spindle speed via mathmatical calculation(headache starting already) . Can anyone turn me onto the equation for figuring this out? The middle pulley will be inverted.
Last edited by catman81056; 03-22-2012 at 05:46 PM.

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how's this

http://www.csgnetwork.com/pulleybeltcalc.html

here's an even nicer one, that once you put in the imputs shows your gear animated and rotatating

http://www.blocklayer.com/Pulley-Belt.aspx

all the best.markj
Last edited by aboard_epsilon; 03-22-2012 at 03:57 PM.

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I've seen those but they only take into account 2 pulleys, I'll have a 3 pulley system. Any mathmatical equation for that?

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well usually it doesn't work ...you must have the same size pulleys as the other set only inverted ...

if not, you are going to get belt tension problems ...as you would need a wide scope of adjustment.

you would do your calculations based on each diven/ driver ..2 pulleys at a time.

three pulleys ..

you would do it with two ..work out what speed the driven intermediate one is going ...and put in the calculator the last two in the train....the intermediate and the last one

all the best.markj
Last edited by aboard_epsilon; 03-22-2012 at 06:06 PM.

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The middle pulley(idler) will be on a pivot, able to move front or rear. Hopefully this will solve the belt tention probs. I'll have to take a few pics of this project to show the final result.
Last edited by catman81056; 03-22-2012 at 09:29 PM.

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In it's most basic form, the pulley reductions multiply to get the final ratio.
If the first reduction is from a 2 inch pulley to a 4 inch pulley, the ratio is
2/4 or 0.5 . If mounted on the 4 inch pulley is also a 3 inch pulley driving a belt to a third 5 inch pulley, the reduction ratio is 3/5 or 0.6. The final overall reduction ratio is 0.5 times 0.6, or 0.3 to 1. Hence, if the motor rpm is 1750, the final rpm will be 0.3 times 1750 = 525.

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Thanks for the help, I had another member email me and gave me pretty much the same equation in different terms and they both work. Thanks for the replies everyone, this question has been laid to rest in my book

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