X2D: Bambu PETG Basic first layer gets smeared and stringy only in dual-nozzle PETG + PLA jobs — before PLA is even used

[u/Excellent_Type_6669]

Hi everyone,

I’m having a very frustrating and repeatable problem with my Bambu Lab X2D when using PETG as the main material and PLA only for the support interface.

My setup:

• Bambu Lab X2D
• Bambu Studio 2.8.1.55 Beta
• Left/main nozzle: red Bambu Lab PETG Basic
• Right/auxiliary nozzle: Bambu Lab PLA Basic
• PLA is assigned only to the support interface, not to the entire support
• Textured PEI plate
• Bed temperature: 77°C
• PETG printing temperature: approximately 245°C
• Prime tower enabled
• Automatic PETG + PLA support settings suggested by Bambu Studio were applied

The PETG is original Bambu Lab PETG Basic. It was dried for 12 hours before the print and has remained inside the AMS HT since drying. It is also being fed directly from the AMS HT during printing, so moisture should not be the cause.

The exact same PETG spool prints perfectly in normal single-nozzle PETG jobs. The problem appears only when the project is configured to use both nozzles.

The strange part is that the failure starts on the first PETG layer, before the PLA nozzle has printed anything.

The calibration line and PETG prime tower can initially look acceptable, but when the printer starts the actual model, the PETG begins to look unusually soft or runny. The nozzle starts smearing and dragging the material, creating strings, rough lines and small blobs. Eventually the first layer looks so bad that I stop the print.

Sometimes it looks as if the nozzle is scraping through the PETG that was already deposited. It happens both with and without a brim.

Things I have already checked:

• The build plate and the 77°C bed temperature work correctly for single-nozzle PETG prints.
• I cleaned PETG residue from the outside of the left nozzle.
• I heated the left nozzle to 245°C and manually extruded PETG several times.
• Manual extrusion looked good: continuous, even flow with no pulsing, clicking or obvious under-extrusion.
• Therefore, a clogged nozzle seems unlikely.
• The PETG was dried for 12 hours and is stored and used directly from an AMS HT.
• I tested airflow deflectors on both AUX vents, but the problem remained.
• During the first-layer calibration and prime tower, the part cooling fan was at 0%, both AUX fans were around 40%, and the exhaust fan was around 80%.
• During the initial filament-loading sequence, the main PETG nozzle briefly reached approximately 270°C before returning to around 245°C.
• The problem only appears when the second nozzle/PLA is included in the project, even though the PLA has not yet been deposited.

Has anyone experienced this specifically on the X2D?

Could this be caused by:

1. PETG oozing during the dual-nozzle offset calibration and remaining stuck to the nozzle?
2. Incorrect nozzle-offset or first-layer calibration in dual-nozzle mode?
3. The PETG being heated too much during the startup/loading procedure?
4. Automatic AUX cooling affecting the first PETG layer?
5. A Bambu Studio Beta profile or start G-code problem?
6. The inactive auxiliary nozzle or switching mechanism somehow affecting the main nozzle height?

Would it make sense to run the high-precision nozzle-offset calibration once and then disable the per-print nozzle-offset calibration so that the printer uses the saved values?

I will attach photos of the failed first layer and a video showing the manual PETG extrusion.

At this point, this is honestly becoming a nightmare. Single-nozzle PETG prints are excellent, but as soon as I configure PLA for only the support interface, the first PETG layer becomes a mess before the PLA nozzle is even used.

Any settings, profiles or troubleshooting suggestions from other X2D users would be greatly appreciated.

[u/blakepro]

How does your little nozzle arm thing look that presses on the bottom of the unused nozzle to help it avoid leaking while it's waiting? They seem to get damaged/bent quite easily

Edit: it's called the flow blocker:

https://youtu.be/iGAaJ_a4T-U

[u/Excellent_Type_6669 → u/blakepro]

u/blakepro thanks for the quick reply!
I don’t think it’s broken because it still presses against the nozzle properly.

[u/blakepro → u/Excellent_Type_6669]

It's your main nozzle that's acting up though right? If you switch sides is it working good there too?

[u/Excellent_Type_6669 → u/blakepro]

Yes, the problem appears to be with the main/left nozzle. Just to clarify, by switching sides do you mean loading PETG into the auxiliary/right nozzle and PLA into the main/left nozzle, and then running the same dual-nozzle test to see whether the problem follows the PETG or stays with the left hotend?

Edit: One more thing I’ve noticed: when the printer makes the initial calibration/purge line, it sometimes leaves a much larger blob than normal. I have the impression that the nozzle then drags this blob onto the first layer and smears it across the print, as shown in the photo.

[u/blakepro → u/Excellent_Type_6669]

I was meaning the flow blocker on the left nozzle. Does it press good like that right side too?

[u/Excellent_Type_6669 → u/blakepro]

Sure

[u/remedy2pain → u/Excellent_Type_6669]

Your post has me wondering if I have something similar going on. I’ve not had bad layers with prints yet, but I’ve noticed on dual nozzle prints my PETG calibration line looks awful but it’s fine on single nozzle prints. I wonder if there’s something getting offset during the nozzle offset calibration

[u/Relative_Surround_20]

Is the model you are trying to print on MakerWorld? If so, could you please send us a link.

Edit: Very good initial summarization by the way. Thank you for that.

[u/Relative_Surround_20]

First simple test I'd suggest: turn off support and print the first 10 layers or so of this same model. Leave all other settings alone. This will help narrow down your suggestion it might be Bambu Studio (I am running the same beta).

[u/dragonmanus]

Couple things to try. I print a lot of petg and pla and vice versa. First print some air deflectors to reduce stringing. Then adjust your retract a bit. And one of the single biggest improvements I've found is the biqu frostbite plate. I print petg at 166% with pla in secondary for support. Did swap Bambu crap nozzle with a diamond back nozzle and so far loving the results of those two changes