Re: [CAD_CAM_EDM_DRO] Detecting a bad stepper motor

Fritz Koenig wrote:

>I'm working on a Brigeport retrofit that has NEMA 42 stepper motors on
>it controlled by a deskcnc board with Gecko Amps running at 7 amps and
>a 50V power supply. Jogging the stages around is fine, there is no
>unwanted noise and they move their repetedly and quickly. However
>when I start running a toolpath, the z stage sounds like it's missing
>counts. The toolpath is the alphabet and my tool is a pen. It's
>jumping the z stage up .25" and then down .25" between letters. (I
>realize this is probably extraneous, but it's how I came to conclusion
>my motor is missing counts because it would try to drive the pen
>through the paper).
>
>Is there any other way to test the motor to see if it's bad? The
>motors look original and the machine is a solid 20 years old. Do they
>go bad easily? Could it be my spindle has to much friction on it? I
>haven't gotten the luber working yet, but there is a fair amount of
>oil on the spindle shaft.
>
>

You could swap the motor to another axis. But, it is not real likely that
it is a bad motor. (There is a possibility that the motor has bad bearings,
that can happen.) But, generally, a failure of the motor will be very
obvious, as it will grind but not move at all, or lose sync at extremely low
speeds. Something you should try is to move the X and Y axes only, and
see if the Z moves. That would indicate crosstalk on the step command
wires. Are you sure the Z is the only axis that is missing steps? Or,
is it
the only axis that is reversing direction every move? You might try a
program that moves an axis back and forth 100 times, and see if it comes
back to the same point. You might also swap the bad motor to another axis
and see if you get the same problem.

Yes, the quill definitely could be binding up. Is this a BOSS machine,
with the coaxial ballscrew ground into the quill? There is a ballnut
held between tapered roller bearings (I think), and driven by some offset
drive system - belt or gears. There are plenty of places in this mechanism
for lack of lube or dirt to bind it up.

What software are you using, what feedrate is programmed for the Z axis,
and what acceleration is it using?

Jon