Calculating timing belt lengths

[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.