Z Axis increasing automatically

[adolescent]

Hi, When doing a 3d cut using a 3020 basic desktop cnc machine z axis is increasing automatically. I have used a 3d STL drawing (bought online, so no issue with model z axis) in artcam and converted to gcode. Simulation seems normal. Used that gcode in mach3. But after running, it is increasing the z axis automatically instead of keeping it fixed. Any idea what might have gone wrong.


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[ygorek]

You need to calibrate the Z axis.

[awerby]

It sounds like you're "losing steps" on the downstroke. When a stepper motor in an open-loop system is unable to reach a commanded destination, the controller has no way of knowing that, so it assumes it got there. When your tool plunges into the material, it encounters resistance that overpowers the motor, so it thinks it's lower than it really is. So when it raises up again, it's starting from a higher position, and goes higher than it should. If this repeats, then the Z axis keeps getting higher and higher.

To combat this, you can lower the acceleration on the Z axis, slow down your plunge, or substitute a ramping-in move for the straight-down plunge, which is less likely to overpower the stepper. All due respects to Ygorek's opinion, but an un-calibrated Z axis would give you a constant, if inaccurate, result. Re-calibration won't help if the zero location of your Z axis is changing.

[ygorek]

The skipping of the steps can also be accompanied by interference from the frequency converter, but you need to understand what leads to skips, or excessive speed, or a frequency converter.

[adolescent]

Thanks for your replies. This is the manual I have followed for tuning the machine : https://www.dropbox.com/s/ocar7xou6k...anual.pdf?dl=0

In the Motor Tuning section z axis Velocity and Acceleration is set to 800 and 100 which is different from X and Y.
For the calibration the machine definitely doesn't move 1mm when I say move 1mm from mach3 in the z axis. But I think that's normal for this machine according to the above mentioned manual by the Chinese manufacturer.
Do you think I should change anything else here ? I have tried by lowering the feed rate but it seems still the same.

Also this post came into my attention: https://www.machsupport.com/forum/in...;topic=15306.0

[ygorek]

We do not trust the manuals in Russia, you will not find anything there, if you want to calibrate the machine, you need to use the Internet, see how to calibrate, and you will understand everything.

[adolescent]

Haha.. ok that makes sense now why you don't trust manual. I will try to re-calibrate the z axis and let you know what's the result.