Z axis shifts during printing

[junhongmit]

Hi! First of all, thank you very much for your excellent firmware! I am using MatterControl to control the M3D printer. However, I noticed that the z axis of the printer always slowly shifts down about 3mm during the printing. This annoying problem results in a shorter and contractive printed model.

I also investigated a little bit. I exported the GCODE and did some test. First of all, I preset MatterControl with the right speed limit, and make sure the feed rate in GCODE is under 960mm/min.

1. X speed limit 1500mm/min
2. Y speed limit 1500mm/min
3. Z speed limit 60mm/min
4. E extruding speed limit 102mm/min
5. E retracting speed limit 360mm/min

• Before printing, the printer is calibrated by G30, the bed position is valid. If I move to position z=0, the extruder hits the bed exactly. After printing, the bed position is still "valid". However, if I move to position z=3mm, the extruder would hit the bed, which means the extruder shifts down about 3mm.
• There are three kind of move commands in the GCODE: G1 X,Y; G1 X,Y,Z; G1 Z. I keep all the commands in the GCODE, After printing, the shifting happened.
• As a test, I deleted all the G1 X,Y and G1 X,Y,Z commands, and kept the G1 Z commands. There wasn't shifting happened.
• As a test, I deleted all the G1 Z and G1 X,Y,Z commands and kept the G1 X,Y commands. There wasn't shifting happened.
• As a test, I only kept the G1 X,Y,Z commands. There wasn't shifting happened.

I also walked through the code and didn't find places that may cause this problem. I was very confused. Could you please tell me do you have any idea where this problem may come from? I am willing to share the GCODE and print setting with you. Thank you very much!

[kirasglimmer]

I can't speak for these printers anymore - but when this happens on my current printer it's due to lose hardware: bed, gantry, etc., On the M3D printers, I had trouble with the print bed moving around during the print. Most likely, it's not a GCODE problem you have there. As the printer rises up, the print can not move underneath. Z shift is almost always some sort of physical problem because it's caused by the part moving during print. If you are printing a tall part, try adding support structures to the sides, sort of like beams leaning up against it.

[kirasglimmer]

Can you post a picture of how this part looks in the printer?

[junhongmit]

Can you post a picture of how this part looks in the printer?

Thank you very much for your reply! Today I changed to use another software named Repetier and the embedded Cura slicer which were tested by donovan6000. However, the Z shift still happened. I am wondering it must be something related to the hardware. Here is the picture of the part I just printed tonight.

It's very suspicious, the Z shift always happens near the bottom. It happens all the time! And I think it's not related to the parts. Because, in all the tests I have done before, I stop the hotend and only move the extruder in the air, the Z shifts still happen!

And as I stated before, only under the particular circumstances, like running the generated GCODE in original sequence will it happen. If I only keep the Z move command, there won't be Z shift, which should prove that the bed and gantry are normal. It's very bizarre.

[kirasglimmer]

Yes, same thing would happen on my M3D Pro. I had set some wedges up to jam the bed into place, which helped a lot. It's nothing in your software or slicer settings, and this model looks like it has plenty of it's own mechanical stability that adding struts would be pointless. I think M3D had a support article on this at one point. I haven't used my pro in years though...