Hi, I have a questech cnc educational mill I retrofitted with PMDX 122 breakout board, PMDX 150 driver boards. The mill is a sherline with oriental PK 266-e2.0a 2-phase stepper motors w/1.8 deg. step. I have read quite a bit of the past posts regarding motor tuning and config. however, I am not clear whether or not I should be using the sherline mode. I am a little confused as to what it's function is. I have finally got these motors to work by jogging. I configured the boards for 1/8 step, which if I understand this correctly, computes to 32000 steps per. with a .050" worm. (200X20X8)
I set the steps per to 28000 and let mach fig. it for me from there and it computed a figure around 31950. It seems really accurate.

1. Do I leave what mach did or do I change it to 32000 even?
2. I did this tuning with the sherline mode activated, was this the right thing to do?
3. What is the best practical, reliable and accurate setting for me to use as a beginner?
4. I set my backlash for Y and seems to come back right on the money however, after finally getting X accurate, it wanted to go past my "zero" .001" each time. Y did not do that. Is this normal and/or can it be fixed? (Even though it is going past my "zero" check, it is also accounting for it, which is right)

Thanks for any help! Colin

1. The correct figure for your steps per unit is the one you calculated (32000) . If you make a measurement it is open to inaccuracy - hence the difference. The Mach 3 figure is 50 pulses out which is over a thousanth of an inch - nearer 1.5thou
2. The pulse time for the step and direction pulses can be altered on the motor tuning page. In Sherline mode this is cancelled and the Sherline system is invoked which is something approaching 50/50 as far as I know. If you have a Sherline system - with Sherline elctronices and drivers then Sherline mode can be used - but if the thing is working satisfactorily in "normal" mode then leave it.
3. Since your steps per unit are incorrect you will have to do ithe backlash again.

Turn Backlash compensation OFF. Zero the axis (Program Co-ordinates). Type G0X1 on the MDI line. Set up your calipers or whatever you are measuring with and zero them. Type G1F4X2 then G1X1 and the carriage should go at a slowish speed (I assume you are in iinches, if metric then multiply all by 25)
The carriage should have returned to where it started, but will not have - and the difference is the backlash. (You can do this several times and average the result if you like, but done carefully, once should suffice. Always include the opening move, which gets rid of backlash).

If you now turn Backlash compensation ON your axis should be accurate. If the axis is coming back 001 too far, then you were not quite accurate, and knock 001 of the compensation figure. (But get you steps per unit right first)