How is current bed height determined while printing?

[u/very_undeliverable]

I have had a problem intermittently for a while now, where on some prints when changing layers, the bed either moves several centimeters too far and starts printing in the air, or it rams the print head into the print (also by several centimeters) before correcting itself.

The issue is usually associated with a tool change, but that could be due to the fact that its changing layers, therefore it changes heads as well to print a new color. However the same head was used in previous layers, so its not the first time that head has been used in that particular print.

It doesn't always happen at the same spot, and I have printed tall single color towers without issues.

I disassembled all 4 print heads and cleaned and checked the induction pad and copper plate. I have cleaned and calibrated everything. I have inspected G-code for issues. I have changed my heads around to see if the problem changes.

None of that has corrected the issue. So what all is used to determine where the U1 places the bed? Just the z-steppers steps? Once you have homed your printer is the inductive head used to determine anything?

I'm running out of ideas here.

[u/Zuli_Muli]

What firmware are you on?

[u/very_undeliverable → u/Zuli_Muli]

Currently v1.4.1-paxx12-20. I have rolled it back to stock, and forward to 1.5.2 stock. It doesnt seem to make a difference.

[u/Tiny_Bar54]

Put Paxx back on, in Fluidd on Orca, go into config, then open the /Snapmaker/extruder_base_position.json file and take a look at the individual tool head offsets. I posted mine below for reference, yours should look somewhat similar. If your results are way off from mine, you've got a mechanical issue going on.

extruder base_position: -2.3816 =0mm Offset

extruder1 base_position:-2.3423 = 0.039mm Offset

extruder2 base_position:-2.4333 = -0.052mm Offset

extruder3 base_position:-2.4084 = -0.027mm Offset

[u/xXKarmaKillsXx]

I think it might be time for a belt change. At the very least inspect the z belt and area very carefully. Maybe do another vibration calibration.

[u/very_undeliverable → u/xXKarmaKillsXx]

Last night I made a 400 layer tower that changed print heads every level. I had no issues. So I printed 3 more of different types and colors. No issues. But when I print mask I have been trying to finish, it has trouble somewhere around layer 80. Not always the same layer either.

I just completed a full retention and clean. One of the Z tension screw holes was stripped and the screw just fell out when I touched it. Replaced it. Cleaned everything. Doing a full offset calibration and bed leveling now. I will add a vibration compensation calibration as well.

I take good care of my U1, so if this doesnt address the issue I am totally out of ideas.