Quote Originally Posted by Robin Hewitt View Post
Is a 10 tooth pulley big enough to hold the belt on a quarter turn? That's 2 teeth.
I was assuming that both pulleys on the shaft were driving, thats 4 teeth and the torque is fine on that...

Is it small enough to get any kind of resolution on a stepper?

A 15mm PCD pulley moves it 47mm per rev.

0.12 mm/step before you start springy microstepping, will that work for cutting alloy?
Probably not, but I don't think you would realistically do alloy on an 8 x 4 router

If you microstep can you rattle the PUL pin on the driver fast enough to get the top speed?
Needs 200rpm for rapids, thats fullstep = 670steps/sec, then microstep for final positioning... needs a morphing driver really but its doable at fixed microstepping 2600steps/sec.

If you gear it down, do you move beyond the top speed of the motor?

Beginners don't usually play with the numbers, they just look for massive torque motors and hope that will make it right. That's why steppers are usually sold by the Newton meter rather than by the torque to speed graph.

130kg belt tension may exceed the permitted side loading on the motor shaft.
It would, thats why it needs the pulleys on a bearing supported shaft (skate bearings OK to 1700N radial force) and the motor coupled in.


Can you actually get a big enough shaft inside a 15mm aluminium pulley without severely under cutting the teeth? I think you will need a bearing either side of it.
Thats an interesting one, and not one I'd considered. The standard 10tooth pulley is a 6mm dia shaft. the upper pulley and lower pulley are in opposing tension so can a 6mm shaft stand a shear force in the middle of 2600N?
I suspect it will need a bigger (more teeth) pulley and the motor will need to be geared down to drive the shaft to get the resolution without too much microstepping. A 20th tooth pulley and a 2.5:1 gearing would give a 30mm dia pulley (good for a 10 or 12mm shaft). One turn of the pulley = 100mm so 0.1mm resolution needs 1000steps, geared down 2.5:1 is 400steps/rev which is 1/2stepping and 10m/min rapids = 100rpm of pulley = 250rpm of motor which is still feasible at 1666steps/sec.

A little maths and understanding to find the best compromise before you build can save a lot of disappointment later. (Please assume a big grin smiley, the new editor restricts my smiley selection, sometimes it shows, sometimes it doesn't).
mine doesnt! :naughty: