If turning down to a specified diameter using the wizard, what is a reasonable accuracy to expect?
Actual turned down diameter will only be as accurate as your lathes "complete system" and additionaly accuracy can be related to surface finish when measurements
are taken on the diameter of the piece. Depends on spindle runout, surface finish, etc.
You have what you have.....!
Moving the slide repeatedly backwards and forwards to the same nominal position, what repeatability can be expected?
Depends on the motors / electonics / drives but also on the mechanics of the system ( backlash / ball screw accuracy).
On my converted lathe repeatable backlash is like .0004 on the Z and even better on the X. The x axis ball screw is a high end ground ball screw.
So in testing using a .0001" indicator or opticaly compared it's on as compared to Mach's DRO.
but I was wondering about just how repeatable microstepping is
Well, for my engraving machine i could not measure it ie; didn't have enough light at 400x to read the calibrated glass scale with a microscope.
I have found different steppers will microstep better than others....Russ gave an example from Geco for the reason.
I can however easily split .001 into 10 parts by jogging in .0001" steps. Now remember that my steps per unit is 253000, thus resolution is
.000004" but practicaly the screws ware only calibrated / certified to .000040" acuuracy over the total movement. As noted by others you will find that
there will be no movement and then the stepper will jump to the next postion and the number of steps can vary over one revolution of the motor. Change the motor and
you will see a difference if you graphed and compared the movements to steps. So not all motors are created equaly.
Now if you had a pulse counter you may also find out that even the tension of a timing belt can influence your readings as even though the motor turned from a pulse there was no
mechanical movement due to the belt tension. We did some testing and found that Mach / the PC provided the pulses but the drives, belting, motor, etc didn't mecessarily react to them all.
Things are just not perfect......!
And what is people's experience of the accuracy achievable with Mach?
Mach is more accurate than your ability to measure the movement..........!
If you have a quality system then you will have accuracy.
RICH