Belt drive on a router

[m_c]

The idea is that I can slacken the belts when not in use then set them by taking up the slack plus 2 turns.

Why?
Modern belts don't stretch.

[Jonathan]

Why?
Modern belts don't stretch.

Everything stretches - it's a matter of how much, which in this case depends on things such as the width of the belt and type of tension members in the belt.

Page 7 of this document has a graph to show how they stretch:

http://www.gates.com/facts/documents/Gf000289.pdf

If you're using the belt on a machine with low or zero cutting forces (e.g. laser cutter), then the gantry can be light so the force should be small enough for this not to be an issue. However if it's for a router as the title suggests I would do the calculation to find out how much the belt will stretch, or at the very least use the widest belt you can fit.

[Robin Hewitt]

Why?
Modern belts don't stretch.

Belts may be modern but I'm not

If the belt doesn't change it's elongation over time when left in tension that could save me a very inconvenient switch. I was thinking to measure the length of the bed in stepper resolution at start up then scale the G code to match.

This is kind of crucial because I have designed for a 3/4" aluminium tube inside the gantry which carries the head control wiring to the flexi cable conduit that connects to the head.

If the belt needs constant calibration this tube goes full length to get a switch at the far end.

If the belt doesn't need constant calibration the tube only goes half way and the fitting is different.

It will be a pig to fix if I get it wrong.

This is the last part before I can fit the long belt, so what do I do? Full width or half way?