My Z axis is the same as Dave's .... 10mm dia x 2mm pitch trapezoidal leadscrew with a delrin nut
(Marchant Dice)
http://www.worldofcnc.com/collections/trapezoidal/products/delrin-nylon-round-right-hand-lead-single-start-nuthttp://www.worldofcnc.com/collections/trapezoidal/products/tr10x2d-trapezoidal-right-hand-spindle-leadscrew-din103-c15-c35I did consider a 4mm pitch.... but would like to make a bit more of an improvement, as my travel distance is about 135mm and I have a 4th Axis (modified rotary table) that I'd like to integrate for doing lobsterback exhaust parts and roll cage / hoop bits.
My X and Y are HTD 5mm pitch belt drive, with direct 20T pulleys.
All belts are mounted on the outside of the rails (opposite to the plasma torch) hence shielded from muck
The leadscrew is not really in the direct line of blowback as there is quite a bit in the way.
Belts are tensioned using some manufactured springs similar to what the 3d printer crowd use with their 3mm belts.
http://i.ebayimg.com/images/g/tEgAAOxyBotTWzgV/s-l300.jpgBacklash is not much at all and not really something I'm concerned with too much with a blunt tool like a plasma (but I'm not doing artwork etc)
I have about 0.16mm (~6 thou) of backlash on the belt drives, but I suspect its the nature of using belts
All my motors are the same as posted earlier 3.1Nm.
I have been fiddling with my settings this morning given I can get higher acceleration that what I was running X and Y and both higher velocity and acceleration Z.... although I need to test it under instant acceleration of (slap and go) of THC as I dont think I had it set up the best following earlier discussions on here as I've learnt a lot.
My X and Y run 10uStep (0.05mm/step [~2 thou], Z is 1/2 step (0.005mm/step [~0.2 thou / step])
The Z can clearly been improved upon given that sort of resolution is not required, I did consider full step (but not sure what others run step/ unit wise on a plasma table)
I don't use backlash compensation.... but I can and hence the 10uStep resolution would tie in nicely with the ~3 steps of backlash compensation.
Again not sure what others do....