Quote Originally Posted by dickieto View Post
slow down a bit irving!! it will take me all night to take all that info in!!!:confused:
only joking, thanks for the calculations.
does this mean i could fit the 10 toothed pulley directly onto stepper motor with out reduction?or am i missing something,i would like to go for bigger motor just incase i was going to do some alloy or do you think this would just be overkill??
i was also thinking of making my own v bearings with twin bearings inside round bar turned down to suit angle iron or do you think this would be to much friction??
sorry for all the questions but its your own fault for being so knowledgable!!:naughty:
thanks again Tom

dont take these as gospel, its a frst cut. I may have missed something, or my approach to estimating how forces giving rise to motion of the gantry translates to torque might be wrong. I dont want to diss your idea, but can't help but think if it was that easy why hasn't someone done it before? I do think the limiting factor might be belt width/torque handling and availability in the lengths you need. One or two suppliers do continuous belts larger than 3.7m which could be cut open, but these tend to be in the 8mm not 5mm HTD and the pricing is >£50 per belt. With 8mmHTD a 10t pulley is 25mm dia so the torque needed at 200rpm is 0.3Nm, and the resolution at 1/4step is 0.1mm. 8mm belts come standard at 30 and 50mm widths

I was working on the assumption that the steppers drive the pulleys directly, but in practice you can't because the shaft length is too short. You will need the two drive pulleys mounted on a shaft in bearings which is driven by the motor via a coupling.

Before embarking on the big build, I would trial a small version of the X say 200 or 300mm square using 5mmHTD and cheap drawer slides from B&Q to measure the loads/forces/etc. operating load could be added by a bit of string running over a pulley to a pan that can be filled with sand or other stuff to see how it performs under load.