Z-axis stepper moves fine with LCD move axis but when printing with Repetier it shuffles and buzzes

I bought a used MPCNC a few weeks ago and am just now trying to get it up and operational.

I’ve got an issue with the z-axis stepper motor or driver. When I use the LCD or Repetier to manually move all axis move properly and the proper amount IE: distance. The trouble is when I send a print the z-axis motor spins all of a sudden and seems to stall or snag thus getting out of alignment. Here is a video showing the behavior: www(dot) dropbox (dot) com/s/9d9zhxya3zbofkm/z-axis.mov?dl=0 Can someone help me troubleshoot this? Is it a hardware issue, assembly issue, or software issue. If the z movement during the LCD or manual movement is working fine can’t I just set that “rpm” or speed in the driver somewhere? TIA

P.S. I’m just getting started so the machine is not organized and the wiring is haphazard. Once I get things working properly I’ll get cable chain rails etc.

It’s an older version of the MPCNC using the MKS v1.2 board with Marlin-MPCNC_Ramps_T8_16T_LCD_32step Firmware.

I was able to stop the z-axis stuttering by changing the default max feed rate and default max acceleration values for the z axis.

You have the allthread Z. Which is very sensitive to Z speeds. A leadscrew is about 4x fewer steps/mm.

You got it nailed on the head that too fast Z is causing lower torque. We usually recommend fixing it in cam, but I am happy to hear the firmware fixed it. It didn’t used to. What controller and marlin version are you using?

A 24V power supply would help too, giving you a higher speed range with full torque. But not all controllers and accessories can handle that.

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Thanks for the reply! :smile:

The controller is the MKS v1.2 board with (user modified) Marlin-MPCNC_Ramps_T8_16T_LCD_32step Firmware.

“We usually recommend fixing it in cam” <<< I’m not sure I understand what that means can you explain that a bit more, please?

In Estlcam, and I think in fusion, you can tell it to add a speed to every move and to limit the Z speeds. Otherwise, you might be doing an XY move at 15mm/s and then lose steps when you try to drive Z at 15mm/s.

Ah yes I’ll see if I can control the movements (Feed Rate) and (tool head positioning) rates in the g-code.

Right now I’m experimenting with Vectric Aspire and generating the G-Code with the Marlin Post Processor and loading that gcode in Repetier.

There is a lot to learn here at the beginning of the CNC road.