Odd Z axis issue

Hello,

I've built a DIY 3D printer from my old CR-10 Melzi board, old some wood and spares from eBay. It's quite 'bodgy' as it is just used for experimentation, so I can keep my main printer (cr-10s) intact.

The X and Y axes are quite conventional. Both are belt driven and similar in concept to the A8, CR10 etc. It works OK with a laser engraver module as no Z axis movement is required.

My problem is that the Z motor is not moving the hot end up to the expected layer height. It gets a 'nudge' when layer height command is set but with barely any movement. The Z axis is driven up/down by a single m4 threaded rod coupled to a Nema 17. I guess the concept is similar to that used with a CNC spindle motor except that I have a E3dv5 clone hot end with bowden tube.

I spent a while looking at mechancal issues, but I now think the issue is with the firmware or a config setting because of the following:
1) I can manually move the Z axis fine using the Move Axis command.
2) I can print objects using Cura spriralise mode without issue. Z axis move fine in spiral mode.
3) Although the Z axis is not advancing with each layer, Babystepping can move the Z axis fine.

It seems as if the Z move command is not being interpreted correctly??

I am running Marlin 1.1.9 and I can provide config files and/or photos on request.

The main Marlin changes are for the calibrated step factors below and a smaller bed size:
DEFAULT_AXIS_STEPS_PER_UNIT { 98.6, 98.9, 4640, 97 }

Any thoughts or suggestions?

regards
John

I think your Z-axis speeds may be too high causing the axis to stall. Steps per unit seems fine. What are your speeds? Try lowering the Z-axis speeds by half.

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http://www.marinusdebeer.nl/

Thanks for the prompt response Ohmarinus

I had already tried 50% speed without success, but your reasoning was spot on so I reduced the speed to 6 (default was 45!) and it now works fine.

I wanted to attach some photos of a calibration cube and a short video but .I just get "413 Request Entity Too Large" errors. The total size is < 4MB. Infact, I couldn't attach 500kb of photos either.

regards
John