Strange Z Axis Behavior

Hello all,

I finally got around to finishing a Mendel I had started several years ago and am very close to a first test print.

I am using a RAMPS 1.4 Board with Arduino 2560.

I am using Repetier 0.92.3

I have Opto Enstops on:

X Min
Y Min
Z Max

I am using a mechanical endstop as a z probe hooked up to the Z Min pins.

When I send something like a G0 Z10 it is only working some of the time. Sometimes the stepper motor just makes a loud hum and doesn't move. It is not consistent but about every third G0 command I send actually works.

G28 always fails on the Z axis. Just a loud hum, no movement.

Strangely enough the Auto bed leveling process works without an issue. When I issue a G32 S2 the whole process completes including the Z axis moving to Z Max and measuring the build height.

Just for kicks, I tried installing Marlin to see if it was a firmware issue. In Marlin the G0 commands seemed to work fine, but G28 still failed.

I have tried all of the following:

Swapped out the Stepper Motor
Swapped out the Stepper Driver
Adjusted the Trim Pot on the Stepper Driver
Routed Z Probe and Z Max wires far away from stepper motors and stepper motor wires
Tried running it with everything disconnected except Z Stepper and Z Max

I have attached my Configuration.h file for reference. Maybe I have something stupid in there. I am so close to having a working printer. This is quite frustrating. Any help would be appreciated.

The humming are lost steps. A typical problem with z axis which needs other acceleration/max speeds then x and y axis. First reduce acceleration to 50. Then start testing z speeds from 1mm/s = F60 to 10. Somewhere there you have a limit speed that you can not exceed, Depending on friction over height it might also only stall at certain regions. That z probing worked means the z probing speed was ok for your printer. Once you know good speeds you can also start increasing acceleration. Normally 100 still works.

Remember that you can and must change these values in eeprom over the host.

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Thanks for the quick reply. I found that I had to change STEPPER_HIGH_DELAY to 1 and reduce my Z speeds to 2 mm/s. I reduced acceleration to 50mm/s^3 as well. Now it is working perfectly. I haven't tried setting acceleration back up to 100 yet. Will try that soon.