I've had a couple of questions about tuning the 4th axis so here goes -
My X and Y use similar steppers, the same settings in Mach3 and my driver boards for X, Y and A are all set the same.
X & Y Steps Per: 645 Velocity: 450 Accell 45
A Steps Per: 35.55 Velocity: 1500 Accell: 80
It will depend on how you have microstepping set on your axes but if you have the driver board for rotary set the same as X & Y then the following should provide a basic start point if you have the same or similar 4th axis:
Divide X Steps Per by 18 for A,
Multiply X Velocity by 3.3 for A
and
Use double the X Accell for A
The Steps Per figure I'm using is only tuned for accuracy over 10 rotations, tape a pointer to the body of your 4th and affix tape with a line on to the chuck to give you a datum.
Align your line with your pointer and Zero A then see how many degrees a full rotation reads, tweak your Steps Per down to increase DRO degress per revolution / up to reduce degrees per revolution.
Once you have one rotation looking good test with 2, 5, 10 and so on until you have the accuracy you want over the number of revs you want, once you are refining for more than one rev you'll be adjusting after the decimal point, at 10 revs you'll probably be adjusting 0.01 in Revs Per to fine tune
Regards,
Nick