Timing belt tension requirements vs backlash

I haven't been able to find any good references or specifiications on required timing belt tension requirements. So I am using the following logic to determine what it should be.

Using the maximum torque rating(840 oz-in) on the stepper motor and its drive pulley diameter(1.5 in), I come up with a force of 75 lbs applied by the pulley to the belt. This force will be applied to the pulling or feed side ot the pulley. If the belt were pre-tensioned by this amount then we would end up with 75 lbs of tension on the feed side and 0 lbs on the other side of the pulley where the belt leaves it. I would assume that there is some initial stretch in the belt as tension is applied but probably the stretch rate would rapidly disappear as the tension increases. Therefore, I would add say at least 10% so that there would still be some tension in the lesser side. So as a result we should adjust the static tension too about 85 lbs.

Of course any angle between the belt and the centerline of the shafts the tension would have to be adjusted by the cosine of the angle. In my case the cosine comes out to .99 which woiuld is neglible.

Hopefully this would minimze backlash error due to belt strectch.

Does anyone with more experience than I in this I have any comments?

Jack Ensor

Have you looked at the belt info at www.sdp-si.com