Z-offset Calibration lost. head "sinks" during Z-Offset calibration.

First up, I'm a noob. so apologies for missing knowledge.

Kit Tronxy XY-2 Pro running latest version of Marlin firmware 2.1.2.1 2003-05-16. Slicer Ultimaker 5.4.0

Too long to read
Z-offset Calibration lost. head "sinks" during Z-Offset calibration.

Having set up the Z axis offset, I have printed some test cubes. I have also designed some parts in Fusion 360 and successfully printed them. All is okay except occasionally after the first print after switching on (and bed levelling) the head crashed into the bed when printing started! (WHY is there no STOP button on the front panel?)

Thinking that I had not stored the Z offset, I recalibrated, and again after switching off and on several limes (after finishing jobs), the Z-offset was lost again! (or so I thought!)

Today, I decided to re calibrate the Z-offset, being very careful to ensure that I followed the correct steps, I set it to 0.25mm as my starting point. Then while still in the same mode (Probe Z-offset | 0.025mm step), I re-watched a video to ensure that I was following the procedure correctly. After a few minutes I could hear vibration coming from the Z stepper and checked the head/bed gap. It was zero! I raised the head a few thou, and sure enough, it lowered into the bed again after a few minutes!

I would like to seek your advice before pulling the machine apart. There must be hold current being applied, otherwise the head would instantly sink and there would be no vibration heard or felt.
I wonder if the hold current is correctly set for this and indeed the other motors?

additional observations.

• While sliding the feeler gauge, one can feel the head "bouncing" under the control of the stepper.
• on finishing a job, on one occasion, the head was observed moving slowly left to right!

any suggestions gratefully received

Kind regards
A

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New to 3D printing Tronxy XY-2 Pro running Marlin

You might be seeing an idle timeout. The default shuts down all stepper motors after 2 minutes.

See the Idle Stepper Shutdown section in configuration_adv.h for details.

You may want to change the DEFAULT_STEPPER_DEACTIVE_TIME or set DISABLE_INACTIVE_Z to false.

Better yet, add a G28 command the slicer's pre-gcode section. This will home the machine before every print. That way the machine is in a known state when it needs to be and you can still save energy by having stepper idle timeout.

@[email protected]
Thanks bob, an interesting area to look at, however the motors MUST be holding as I was alerted to the problem from the noise of the Z motor "chattering" (causing the frame to buzz when the head reached the bed) so the motor was clearly being driven. The "chatter" may point to an inadequate DC current being supplied to the motor, and so collapsing, causing the motor to pull in and out.. or perhaps a poorly smoothed DC is injecting AC ripple. conjecture, but either may may be causing the motor to cog forward. The PSU looks pretty chunky and capable, but could be faulty of course.

I am on holiday ATM, so cannot check, but IIRC, I have a pre start-up sequence that homes, bed levels, and then prints a stripe down the left of the bed to ensure that the head is primed.

Again, thanks for your input Bob. I will check when I get home next week.

Kind regards
A

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New to 3D printing Tronxy XY-2 Pro running Marlin

The only other thing I can think of is the TMC drivers have a standby current. Maybe the standby current is too low.

From what I can tell your printer uses TMC-2225-SA in standalone mode. I didn't find any documentation on how to set standby current in this situation.

You might want to try increasing stepper current and see if the hold issue goes away.

Thanks all for your input.
The issue has gone away!

However I have found that when tramming, if another movement is called (say Home), the head will keep moving in the last direction and of course crash if moving away from the limit switches. In addition if pause print is called, resume is (correctly) displayed, however, when pressed, it does not show Pause! Although, the functionality for multiple presses is correct! does not fill me with confidence. I will report these bugs/unexpected behaviours

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New to 3D printing Tronxy XY-2 Pro running Marlin