Oh...
before I get shot down on the general statement of 8uSteps per full step...
It came from here (sort of) [4th paragraph down]:
http://www.geckodrive.com/support/step-motor-basics/accuracy-and-resolution.htmlAny microstep resolution beyond 10, such as 125, yields no additional accuracy, only empty resolution. By analogy, a voltmeter having a 6 digit display while having 1% accuracy would have meaningful information only in the first two digits. There are two exceptions justifying higher resolutions: The step motor is being run in a closed-loop application with a high-resolution encoder or the application requires smooth operation at very low speeds (below 5 full steps per second).
You could also use 10 u steps / full step (setting 2000 >>> ON-ON-OFF
which would be:
Metric: 2000 steps / mm
Imperial: 40 000 steps / inch (1574.803149606299 steps / mm .... same as DouglasDrew in his post above.. (almost... may have a little more inaccuracy though)).
The velocity and the acceleration really need tuning in my opinion, the acceleration is by far the more important factor given it will lead to lost steps as most of the time whilst the machine is under load it will be running at a lower velocity (feedrate) but the acceleration would remain the same....
If you are loosing steps, you may consider either lowering the acceleration, or retuning the machine to 8uStep / full step resolution ..... or increasing the supply voltage to the motors (check the drive limiting voltage!!!!! Including deceleration voltage generated or you'll kill the drive..... Toroid transformers tend to be better than switched mode (mine sounded rough when I ran one but I was running at a faster pulse speed at full velocity though than yours would be running (not mill ... plasma).
Rob