Designing Timing Belts, Pitch Diameter ~ Outer Circle???

[laminar-flow]

The project is to calculate the timing belt length when buying two pulleys. On McMaster the pulley shows the pitch diameter and the belt shows the outer circle diameter. I can't find the belt thickness anywhere which is what I think I need to accurately size the belt length. Is there something I am missing?

 

[EmGo]

In theory, for the toothed belts I've seen, the "pitch diameter" is calculated in the middle of the belt (crosswise) ... but I don't see the point, it's an imaginary number, what you'd normally care about is the number of teeth and the o.d. ?

 

[Peter Neill]

We probably have a dozen or more timing belt drives on every machine we design and build, and we just use the calculator from Optibelt to find belt length. There is a formula for calculating belt length, but believe me it's a long winded thing - the calculator will give you the best answer and belt suggestions in seconds.
All you need are the timing pulley pitch diameters and the distance between centres to find the right belt length (or the closest length to it).
I can't access our calculator as I'm still signed off work recovering after a heart problem (and the Optibelt calculator needs a pre-approved download), but I can give you a link to another online one I sometime use, but there will be more than a few calculators online to use.

Timing Belt Finder / Calculator - Determine which Timing Belt you require :: Bearing Boys.co.uk

Determine which Timing Belt you require

www.bearingboys.co.uk

 

[SteveF]

Gates also has good info and calculators on their web site.

Calculators

From energy efficiencies to ROI, our industrial calculators show how much time & money your operations can potentially save when you choose Gates.

www.gates.com

 

[Erich]

With timing belts, the pitch diameter is a larger number than the OD of the teeth. It corresponds to the location of the reinforcing fibers.

 

[dgfoster]

SDP/SI has been my goto. They carry a number of brands and their website has lots of background design info.

SDP/SI Website Link.

Denis

 

[laminar-flow]

Thanks everyone. That helps me a lot.