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Belt lengths
MakeEverything - 30/7/10 at 02:14 PM

For the life of me, i cant remember the formula for calculating the length of a Vee belt on three pulleys.

Can anyone shed any light on this please?

adithorp - 30/7/10 at 02:28 PM

I've never tried it but I'm told this works...

Measure around pulleys with string in the bottom of V (l).
Measure depth of V in pulley (r).
Then the external length of the belt (L) is 2 x r x pi + l = L

blakep82 - 30/7/10 at 02:57 PM

don't you just wrap a bit of string round it (with the tensioner at its smallest setting) and measure the string? then do the same with the tensioner at the longest setting, and get one somewhere in the middle?

adithorp - 30/7/10 at 03:08 PM

No because belt lengths are the external measurement and the string measures the inside. there'll be 20-30mm difference.

MakeEverything - 30/7/10 at 03:30 PM

quote:
Originally posted by adithorp
No because belt lengths are the external measurement and the string measures the inside. there'll be 20-30mm difference.


Well, i measured the belt at 890 and added 30mm for the belt thicknesses around the pulley, but when i went to halfrauds, their belt is 1000mm.

Ive fitted it, and im glad i didnt go any smaller.....

MakeEverything - 30/7/10 at 03:35 PM

quote:
Originally posted by adithorp
I've never tried it but I'm told this works...

Measure around pulleys with string in the bottom of V (l).
Measure depth of V in pulley (r).
Then the external length of the belt (L) is 2 x r x pi + l = L


Using this would have given me a belt length of 952..... Maybe as a minimum, but being 50mm out (2" would be too tight and i wouldnt get it on.

blakep82 - 30/7/10 at 03:59 PM

well if you did it with a tape measure it would sit on the outside of the pulley

designer - 30/7/10 at 04:13 PM

Why not go to the local factors and buy a metre of this stuff?

http://toolmonger.com/2009/04/24/fenner-power-twist-v-belts/

MakeEverything - 30/7/10 at 05:22 PM

quote:
Originally posted by blakep82
well if you did it with a tape measure it would sit on the outside of the pulley


If i did it with a tape measure on the outside of the pulley, it would be too big....???


No, i did it with string.

tomgregory2000 - 30/7/10 at 06:16 PM

this is when it is handy to keep old belts and then play the cut and shut game and then measure