I was attempting to calibrate my nozzle height last night and wasn’t initially able to get the process to complete. I figured it out, but I figured it might be good to post about this in case someone else runs into the issue.
What was happening was that the nozzle would go down to the PCB, trigger the Z limit switch, and then back off. This is all working fine.
The next step was to jog the nozzle up until it just barely touches the PCB. However, when I did this the Z limit switch would trigger and cause an error in the tinyg. Based on my experience with homing and checking limit switches, and error when a limit switch is triggered means the software isn’t expecting that limit switch to be triggered.
After thinking and reading a bit, I discovered my problem was with the pickup tube movement resistance. It is critical that the nozzle adapter compress only after the Z limit switch is triggered. Since I had too much pickup tube resistance the nozzle adapter spring would compress first (Juha does mention this in the documentation). This hoses up the calibration process, since it is assumed that the small back-off after the Z limit switch is triggered will un-trigger the Z limit switch.
I addressed this problem by loosening the A axis motor belt slightly, and more importantly loosening the top pickup tube bearing mount, moving the pickup tube back and forth, and retightening the top pickup tube bearing mount. This removed much of the resistance to the tube moving, and now that the nozzle adapter compresses only after the Z limit switch is triggered, the calibration process succeeds.
Also, when I had partially removed the resistance to the pickup tube moving I was able to complete the calibration process, but the backoff value was very low (like .2mm was the best I could get). To get a higher backoff value the Z max limit switch needed to be moved down. When I attempted to do this the switch immediately triggered. This was again because the pickup tube had too much resistance, and wouldn’t fall all the way down (it was stopping maybe halfway through its travel).