Determining belt length

Hi, Please apologize the stupid question, but what’s the correct way to determine the belt length WITH an IDLER pulley. I measured the inner length of the belt band (see below) but I’m not sure if this is right!?

Seems legit.

Got to say, That’s awesome…

The Idler prolly only adds an additional ~5mm to your belt length in its loosest position.

Is that about what your math shows?

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Nah, yeah somehow. The measurement just shows where I measure the belt length. I am not sure if measuring the belt length on the inner side is correct. I would assume the neutral axis is what I have to take into account.

image (Source:

Count the teeth multiply by 5… Belt length.

The issue is, I set the amount of teeth in the model. So, the difference between 62 and 63 for example is so minimal but gives you a different belt length. I need to know where the band length is measured and then I’ll apply the corresponding number of teeth which you can figure out e.g. here:

The total length of a tooth including space between teeth is 5mm

Meaning a 2 tooth belt is 10mm. A 40 tooth belt is 200mm. Model your belt like this? From the inner face of the belt at the surface of the gaps is where it’s measured

Yeah, maybe I could do this. Just need some restructuring.

Measure from this surface marked in pink… sorry for the shitty finger line

This is what I did so far …

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Ok, I think I found it. The belt length is referred to the pitch length (sort of neutral axis) and not to the inner belt length. That’s why I had some discrepancies in the model.

Fits now :slight_smile: