[3.5b1+] Inaccurate print dimensions

Diamondback

On the other hand, since mesh bed is active (and used), Z really shouldn't stay completely still for any amount of time for the first few mm, so not sure why it would enter idle?

dc42

@Diamondback the motors only go into idle mode when there has been no motion at all (on any motor) for the idle period. So the Z motor will not go idle during a print, except when the print is paused or waiting for something to heat up.

Diamondback

@dc42 I see, that is good to know. I guess, this is not the issue then. Any further ideas?

IndeX4D

@Diamondback
I have a similar problem on 2 different machines. Both were working correctly with 3.4.5 , now I have some Z high issues on both.
Multiple / 4 z-axis at work.

Richard

Diamondback

@dc42
Here's two example prints, same gcode, 3.5b1+ printed first, then back to 3.4.5. Both were printed directly after the other as quickly as possible, no changes to config etc, purely the firmware was changed.

3.5b1+:

3.4.5:

The height difference is fairly small here (~0.6mm) compared to my previous issues with the MFM housing, so it looks like the issue somewhat depends on the actual print file.

@IndeX4D since you also mention multiple Z steppers, maybe something related to that?

IndeX4D

@Diamondback

I had 2 prints with machine 1 (GeneralG) where I had little extrusion problems..... after a little pause, the nozzle crashed into the model.
Objekt high 90mm. Problem started at about 50mm.
Extrusion problems -> may missing z steps?
Nozzle crash into model after PAUSE --> missing offset or much more z steps were missing? (about 4mm-->like other problem with machine 2)

I thought somthing is wrong with my axis and because I wanted to change the x gantry, I stopped printing with machine 1 (Generalg).

Then --->

1.--> Machine 2 (Black Flamingo) lost steps after every print, because I had to readjust z every print start something between 0.2 and
0.6mm. Missing z steps in this case are NOT shown in the model but It was a 10mm high print only. May it´s losing steps by any other action. Finish print or start print?
It´s definetely not normal to readjust z offset after every 45min print. Print looks nice but Z offset needs to readjust? Strange

--> 2 . Nozzle crashed into heatbed when executing ´´print again´´ - I think printer ´´forgot´´ the z offset. (4mm). Tool was already coupled from print before.

R.G.

IndeX4D

EDIT: when resuming after pause, the offset? is not applied anymore... nozzle crash.

Maybe --> same behaviour when execute print again or tool change. I Will test a bit more.

Philippe71

I have exactly the same problem with a Duet3-6HC + exp3HC + 3.5b1+.
Same problem as on the pictures.
I went back to version 3.4.5, everything works again (same GCode, same configuration).
Currently my machine is printing, I will switch back to 3.5b1+ and send an M98 P "config.g" and M201, M203, M566 and M906 when it is finished.

dc42

@Diamondback it looks to me that at some layers Z has not moved as far as it should, hence the extrusion bulges. Can you tell if it is all three Z motors that have not moved, or just one of them? If you can't tell, are you able to print e.g. a large hollow cuboid so thay you can tell?

@Philippe71 do you have a single Z motor, or more than one?

Diamondback

@dc42 The bulged lines go around the whole print at the same heights, so I would guess that it's all 3 motors? Do you want the cube in vase mode or normal? What wall thickness?

dc42

Hi @Diamondback, vase mode is different (Z changes continuously) so it might not show the same effect.

Diamondback

@dc42 So I printed a 75x75x50 empty cuboid on 3.4.5 (came out perfectly as expected) and I am now printing the exact same gcode on 3.5b1+.
Interestingly there does not appear to be any issue whatsoever this time around. The print looks exactly the same.
Things to note:

Wall thickness of 1.2mm/3 walls @0.4mm
There's no retractions going on (the previous prints with issues did have retractions)
I do not use Z-hop with retractions, Z only ever changes with completed layers and the active mesh leveling

Diamondback

@dc42 Two more images. The first shows the difference between a "well" printed (3.4.5) MFM housing variation and a faulty (3.5b1+) one, note the stark difference in the height of the posts, this is not a result of the viewing angle. Also note the bulging extrusion again. (one is rotated 180°, so don't be confused by the different sides being visible)

This one is the faulty one alone, note how clearly the hole in the front is not round at all, again this not an illusion from the photo.

(Sorry for the weird colors in the photos, looks like my phone is doing some over the top HDR stuff or something...)

Philippe71

@dc42
There are 2 Z motors

MaxGyver

@dc42

I can confirm the problem. With 3.5b1+ layers seem periodically “squished” in Z direction, almost like Z-Wobble.

My setup:

Duet36HC with 4 Z-Leadscrews.
Bed tramming is performed before every print, and mesh compensation is active.
I also redid the mesh probing after updating, just to be sure.

Diamondback

@dc42 anything else we can do to help you diagnose/replicate the issue? Looks like so far, everyone here has more than one Z stepper and is using active bed tramming?

oliof

@Diamondback maybe try printing without bed compensation to see if that triggers the same issue. Use a raft if required to ensure bed is not causing issues.

dc42

@oliof said in [3.5b1+] Inaccurate print dimensions:

@Diamondback maybe try printing without bed compensation to see if that triggers the same issue. Use a raft if required to ensure bed is not causing issues.

An excellent idea! Right now I don't know what is causing this issue. Knowing whether bed compensation is implicated would help me to narrow it down.

Diamondback

Ok cool, I can disable both mesh compensation and active leveling. (the leveling part before each print is not really needed anymore anyway since I upgraded my spindles to finder pitch)

oliof

@Diamondback if you disable two things, please make three runs: One without both, and one where either or is disabled

@dc42 the reason I thought of that is that elsewhere I recently helped debug an issue that looked like bad segmentation, but it was low Z jerk and acceleration combined with bed compensation that looked like the bulging corner issue.