Another Filament Changing Issue

I am using custom gcode:

M400 U1
G28 X Y

I insert the code at the layer I want to pause.

Upon pause I unload the filament. I load new filament by manually heating the nozzle to 220c and extruding until I see the new color. Then I simply resume print. This seems to have resolved the layer shifting on the x-axis, but I don’t know what is going on here…

I will also note that both colors are the same brand of PLA+. For the calibration cube I started grey and switched to green. For the corner panels I had started green and then switched grey. The issue does not occur if I do not change filament.

Does this only happen with these exact two filaments or with all filament changes?

That’s a wonderful question. I’ll have to run some more tests with the calibration cube. I was having issues with layer shifting earlier, and these were my two subsequent tests running the custom g-code. I haven’t tried with other colors, but I’ll give it a go. Seems strange the edges start to shrink\collapse regardless of which color I start with. :frowning:

Yes, it looks strange indeed. Even more strange that it does not happen right after the layer change, but seems to be fine for quite some layers before it happens and recovers itself for the cube afterwards.
The same prints in mono color work fine?

Yes, mono color prints print fine.

I will try on my side here if I can replicate the issue. With AMS I never had such an issue at least, so I will try the manual change with PLA. In 20 mins I should have a result.

So, my print turned out fine.

I used manual M400 U1 and G28 X Y G-Code pause and unchanged, generic PLA filament profile.
Since I used Orca Slicer, I used Arachne wall generator. What settings did you use?

I just used the generic pla profile, normal speed, g-code pause, I believe everything else was default in Bambu Studio slicer.

I’ll run a couple tests tomorrow using the included bambu filament and just remove and readd the exact same filament and see if I get the same results. I’ll also test some different colors of this filament. Maybe I can try to figure out if I can slice it with the pause in cura or something too. I don’t know if testing a different slicer will help, but I am at a loss.

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How is the dimensional accuracy of the print? On the picture it looks as if the cube is quite “bowed”.

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Both are within .1mm on all sides… it’s pretty accurate, deformities notwithstanding. They do look kinda bowed in the pictures, but they are not in person.

When I look at your last picture, the two colored one appears to be bowed even before the color change occured, at least the edges of both prints do not appear to be line up and be parallel.
I must admit, I have not seen anything like that before and I am unsure how a stop code could produce such a result even before the stop code was executed.

I laid them down side by side with a light behind them, and you are correct, the one with the color change begins warping before the color change.

After my current print is done, I am going to be testing some more. I’ll post some additional pics tomorrow, and my findings, if there are any.

So I printed another one using higher quality filament than I was using. I ran it using the standard bambu pla profile again with a manually added stop. It is definitely much better, but there is still some funny business going on. The faces either side of the x both still bow inward a bit on both the white and brown areas.

This was printed using some of the green I was using earlier. There is no bowing or significant issue printing monocolor. The pillars on this are about twice as tall as the calibration cube.

How do you have them oriented/located in the printer? What are your fan settings when you pause? Are you ventilating? How long is the pause? Can you confirm the bottom color isn’t deformed before the second color gets printed on top of it? I am wondering if you have some sort of heating/cooling issue that only occurs during the pause.

Maybe this type of issue is causing the first color to shrink a bit after the second color gets printed on top of it. Too large of a temperature difference between the two filaments after the pause? Or maybe fans changing during the pause is changing the temp settings in the chamber? Maybe the second color is being printed too hot on top of the first one after extrusion? Could explain why the quality seems to recover later in the print after the temperature has evened out.

The filaments don’t seem to be the issue if they print fine on single color. If the speeds are all the same for both prints, it’s gotta be some inconsistencies during and/or right after that pause if the first color isn’t warped right before the pause.

I am printing the calibration cubes individually, roughly in the middle of the printer bed. I’m using a p1p, no sides. Part cooling is set to its default settings in the bambu slicer. When the pause command happens, the extruder moves over to the waste chute. I am not sure how to answer your question about fan settings during the pause - not sure since the print head moves away from the part anyway. I am nearby to the printer, so I essentially immediately unload the filament and load new filament. The filament changeover takes … roughly 60 - 90 seconds before I resume print.

Yes, the print does begin to warp before the color change on the two color parts.

Ok, so according to the slicer, it should be cooling at 100% the whole print - this is the fan speed setting for the slice with a manually added pause:

Just out of curiosity, why are you manually adding G-Code to Pause?

Bambu Studio and OrcaSlicer both have ‘Pause’ built in. Right click the Layer Slider on the right:
BL Studio - Pause Print Add G-Code

Also - are you using Studio or OrcaSlicer? You’re running XYZ cubes which is usually done when someone is tuning. OrcaSlicer offers many more built in tools to Calibrate. Check here:

Hmmm, that kinda disproves my theory.

Especially since you’re not enclosed (so probably no heat creep or anything like that) and you’re not letting it sit for very long. Weird that it starts to deform even before the color change but doesn’t do that for single color.

Can you check the travel speed? Does it slow down before the pause? What other variables could be different?

I am using bambu studio. I am manually adding the g-code to pause because of an apparent layer shifting issue with the manual pause button on the printer and the “add pause” option in Bambu Studio. Upon resume when using either the pause button or the “add pause” option in the slicer, I get about -.5 to -1mm of X axis layer shift after changing filament. If I just pause and resume there is no layer shift. I think the running theory has something to do with the load\unload commands and the cutter.

When I use the manual g-code option, I do not get the layershift, but I do get the strange problem described in this post.

I am planning to try a different slicer today to see if I get the same result. I can also set the pause command in studio let one of the layer shifted prints finish to see if it experiences the same warping.

I am not sure if any variables are changing as a result of manually adding the pause. I am going to test some additional things today and post results. I’m running bambu’s default travel speed settings for generic pla. Mono-color parts are printing amazingly well - the capabilities of this machine are incredible. I am still printing some functional and decorative parts between all the testing. These corner panels for the P1P printed overnight beautifully. No warping, everything solid and straight. I swear I am slicing these things the exact same way as the calibration cube with the single and only exception of the manual g-code stop and filament change.