Hi everybody,

I have encountered an issue which almost killed my Z-axis assembly, hopefully someone can help me out.

I have built my own CNC router using an ESS, MB3 breakout board and cl steppers from stepperonline. The problem occurred as follows i was running the attached gcode file and it started fine but after a few minutes it started to plunge too deep into the part so i stopped the machine and noticed that the Z0 had shifted down about 15mm, nothing seemed wrong mechanically and the z axis still moved fine and without losing position. To isolate the problem i ran the program again without an endmill installed and sure enough after a few minutes the machine moved down way too far, the Z0 had shifted down 40mm. Does anyone have a suggestion as to what the problem could be?
other possibly relevant info:
-the stepper drivers are not throwing an error
-none of the cables have come loose
-the Z-axis assembly moves freely without (significant)backlash or binding
-on the dry run the spindle was off so no interference from that cable
-Z-axis does not need to move faster than it is capable of

When this issue occurs does the on screen DRO reflect the altered Z location?

This is significant because the DRO information comes from the ESS which reports where it thinks the Z axis is positioned. If the problem is in the Mach4 trajectory control process, then the position reported by the ESS would reflect the error. If the DRO still shows the correct Z location where the axis should be, but isn't, then the problem is happening in the ESS step generation or somewhere downstream from there.

When this issue occurs does the on screen DRO reflect the altered Z location?

This is significant because the DRO information comes from the ESS which reports where it thinks the Z axis is positioned. If the problem is in the Mach4 trajectory control process, then the position reported by the ESS would reflect the error. If the DRO still shows the correct Z location where the axis should be, but isn't, then the problem is happening in the ESS step generation or somewhere downstream from there.

Hi, thanks for the response!

When the issue occurs the DRO does not give an accurate Z-position, the actual position is much lower than the value given by the DRO.

Thijs

I would suggest that you temporarily disconnect your Z axis driver from the ESS/breakout board and connect the ESS/breakout board output for the Z axis to a different axis temporarily and see if you can cause that axis to show the same symptom of incorrect "Z" location. That would help determine if the problem is in the ESS/breakout board or in the driver, motor, and mechanics. Be careful that you have room for the motion intended for the Z axis to happen on the substitute axis while testing.

Thanks for the tip, i tried slowing it down and seeing what happens, and what do you know...

i don't think the stepper is losing steps as it would throw an error so I think/hope the coupling is slipping. It would also explain why it shifts down, because it slips when trying to go up to fast.