Losing Z steps

I am using EMC on a Harbor Freight mill retrofit (using a Geckodrive G540 parallel port driver for the steppers) and while it has been working great, I recently tried to do some engraving, which has some very small motions in the Z axis- The tool position gradually gets higher and higher above the workpiece, and if I let it go, after 10 characters, it is easily 0.1" above. I tried working with the g-code to make the Z motions integral multiples of the step size (even moving to the raw step size to try to eliminate the microstepping), but that doesn't improve things. Thankfully, the error is always positive, so the tool moves away (rather than deeper) from the workpiece. This is really frustrating, and I'm not sure what is the best way to further diagnose this problem.

Regards,

Matt

if your using microstepping , i'd try reducing the microstep , also you say adjusting the step size to suit z motion's ?
give the indications of the type of ballscrew size , pitch , any belts etc and lets see , how the figures work out etc

I'm driving the motors at 24V at 2.2A. The motors are rated at 2.5A. I will try running the tests you pointed out. I see that the test program points out if I have a problem, but what is the best way to choose the values? I was pretty conservative when I did the initial setup, keeping the max velocity and acceleration low (This is a hobby setup and I did not see a need to push the limits for speed, particularly as I'm also learning at the same time).

While I didn't adjust acceleration in my engraving file, I did experiment with keeping the feed rate very slow- down to 0.1 ipm, and that did not affect losing steps- I still lost steps.

Looking back at the initialization files, I may have made a mistake in my calculation with respect to adjusting for step size- I had calculated the step size multiple with respect to the X/Y, which is 32,000 microsteps per inch, while the Z is 20,000. Even with using a non-integral size, I shouldn't be losing steps, right? Particularly if I'm just transitioning between 2 different Z positions, one for cutting, and the other for moving to the next spot.

Thanks for the help. This software (and community) is pretty awesome.

I ran the code that you (John) suggested- and the tool ends up exactly at .5 above the table- I lower it to zero, and it was perfect.

From your experience, does this mean that the acceleration is set to an acceptable level? I understand I could do better if I went to a higher voltage drive, but as I understand it, it isn't the root of my problem.

I don't have any binding in the Z axis. I'm using the spring arm that came with the mill as the counterbalance- I understand that it doesn't provide near 100%, but it is something.

When I first tried, the spindle was off, but I tried it with the spindle on (at about 75% of max speed, the speed I was running when trying to engrave) and the results were the same- after the test, the tool was exactly 0.5" above the table. I think I will try this while only moving a very small amount and see if this reproduces losing the z steps.

I'm quite open to other experiments/suggestions.

FYI: I have not adjusted the trim on the geckodrive- it is as it came from the factory.

You could try running the test again but with moving the x and y axis at the same time, perhaps three axis moving at once is pulling the power supply amps down.
Are you sure you are not trying to lower the z axis into the work too fast when running your program? Try lowering the z axis speed even lower.

Rick G