Quote Originally Posted by Jonathan View Post
1) All the C7 screws I've got have been <0.001" backlash... even after a fair bit of use.
Interesting, they must be well within limits.
Also, I'm not sure, but I reckon the delrin nuts will be a lot more 'springy'.
Of course, delrin is about 50 times more "springy" than steel but the springs in antibacklash nuts should compensate.
Either way for a mill your best off using two ballnuts with a spring in between to eliminate backlash (google it).
A bit beyond my budget. It would also reduce table travel too much.
2) No, luckily that's not right. The stepper motor torque is vector sum of the motor winding currents, so 1.41 (root 2) for full step and 1.00 for a microstep drive. However that doesn't apply now as for over 10 years microstepping drivers have used morphing, distorting the waveform from sine/cos to closer to square to achieve the full torque.
Sorry, I don't understand this but my electrical engineering degree was obtained 44 years ago. I'll have to do more reading! Can you give me a technical reference?
3) Advantage for ballscrew as the higher pitch means screw angular velocity is much less, so the inertia and thus the energy the motor has to impart into the screw is a lot less. May not be that significant compared to the relatively high coefficient of friction of dovetail slides, but definitely is on a machine with rolling bearing slides.
Agreed, inertia is not a concern for a small mill with dovetail slides.
4)Ballscrew definately wins ... hardened metal rolling versus hard steel *sliding* on plastic!
Agreed, ball screws will wear much less but is it significant for a hobby machine?

Thanks for the replies chaps.

Russell.