I've restored a big old PTO driven band saw to run on an electric motor just need to buy some belts before it cuts wood for the first time in 50 odd years I'm guessing.

I've never had much luck buying the correct length of V-belt first time. There seems to be loads of online calculators but most don't say if they want the actual pulley diameter the pitch diameter etc etc.

I have two pullies at 20.75" centres. One pulley is 3.25" total diameter (3" pitch diameter) the other pulley is 8.5" total diameter (not sure the pitch diameter for it is but its the same 'A' grove geometry as the small one so Im guessing 8.25" pitch diameter).

I've tried a few online calculator and they all give different answers.

So when I walk into the V-belt shop what length do I need to ask for?!

Many thanks for your help in advance, and go easy on the belt length related jokes!

How about using a piece of string or cord to lay along the run of where the belt will go and then measure it's length when removed. That is what I did when I converted my GT6 from dynamo to alternator charging system.

as above, that's what I did

set the adjustment 1/2way, bit of cord and measure.

that sounds logical but would come up rather short as the belt shouldnt touch the base of the grove, infact your better off wrapping a clothes tape arround the outside of both pulleys. It's one them, I've only got scope to move the motor side to side an inch to take up the slack, I often end up buying a belt, cutting it and measuring the difference between that and what it should be. on a 60" belt there's going to be some strech to.

You can buy adjustable v-bely by the length at most bearing suppliers.

I agree with the rope/string theory. To get a belt for my old lawn tractor I got a piece of rope that sat with it's widest point half-way down the V, this was not perfect but it worked OK. I guess if you have the angle of the V too that would help the supplier choose?

HTH

By my rough calcs, it comes out at 59.5" working on the pitches. The tangential lengths for each side are 20.6" and the angular difference for the contact is 15 degrees total per end, 165 degrees contact for the small pulley, 195 degrees contact for the large. That gives 4.3" circ on the small and 14" circ on the large pulley, therefore 59.5"

Many thanks folks. I worked it out to be between 59 and 60 inch to. I will get a 59 and keep fingers crossed

as said, if the pulleys are in the centre of any adjustment, an inch can be tensioned out.