Belt drive on a router

[m_c]

Belts offer numerous advantages for driving ballscrews, the stretch is almost invariably negligible there since the belts are very short. However if you're using belts to replace ballscrews (i.e. the subject of this thread), then the stretch will be a factor - otherwise belt driven machines would be good for machining more than just soft materials.

Stretch/Elasticity during use will be a factor, but loosening the belts of when not being used is going to have a neglible effect.

[Jonathan]

Stretch/Elasticity during use will be a factor, but loosening the belts of when not being used is going to have a neglible effect.

Agreed..
The manufactures do say you should check the tension after running for a little while as they stretch a bit when first installed then 'settle down'.