Calculating timing belt lengths

[Neale]

If I am aiming to use a couple of 20T HTD5 pulleys, and not allowing for potential pulley change later, what kind of adjustment should I allow for belt tolerance, stretch, fitting, etc? The steppers will be mounted on plates with slotted holes for fixing and with due allowance for the central boss. Nominal pulley centre-centre distance is 115mm. I've never used these things before so not sure what a sensible range of adjustment should be.

Posted in this thread as it might be useful information for others.

[Clive S]

If I am aiming to use a couple of 20T HTD5 pulleys, and not allowing for potential pulley change later, what kind of adjustment should I allow for belt tolerance, stretch, fitting, etc? The steppers will be mounted on plates with slotted holes for fixing and with due allowance for the central boss. Nominal pulley centre-centre distance is 115mm. I've never used these things before so not sure what a sensible range of adjustment should be.

Posted in this thread as it might be useful information for others.

Neale slots of about 40-50mm would be fine and certainly make it easier to put the belts on.

[Neale]

Thanks, Clive, and you have reminded me that I need to allow for the flanges on the pulleys so a bit more adjustment needed than I was thinking - but 40-50mm seems fairly generous? I was thinking of more like +-5mm?

[Clive S]

Thanks, Clive, and you have reminded me that I need to allow for the flanges on the pulleys so a bit more adjustment needed than I was thinking - but 40-50mm seems fairly generous? I was thinking of more like +-5mm?

The longer slots are to be able to change pulley size if needed and also so than it will fit a small range of belts sizes.

[Robin Hewitt]

I don't allow for any adjustment. That's the wonder of CNC, you cut it right and everything fits