Issue with auxiliary/right nozzle on Bambu Lab X2D when printing supports

Bambu Lab X Series Bambu Lab X2D
1

Printer: Bambu Lab X2D.

I am using both nozzles: the main nozzle prints the model, and the auxiliary/right nozzle is assigned to print supports or support interface layers.

The issue happens specifically after a tool change from the main nozzle to the auxiliary/right nozzle. When the right nozzle is supposed to start printing support, it moves along the toolpath, but filament comes out with a significant delay. Sometimes the nozzle just moves over the support area without extruding properly, then spits out a few small blobs of filament. As a result, the support does not form correctly.

Important detail: if I print a separate test object using only the right nozzle, extrusion looks normal. So it does not look like a constant clog or a complete feeding failure. The problem seems to happen specifically during the transition from the left/main nozzle to the right/auxiliary nozzle, when the right nozzle has been idle and then needs to start printing support immediately.

I have already performed manual Flow Dynamics Calibration for the right nozzle. In the newer version of Bambu Studio, manual Flow Dynamics Calibration for the right nozzle is available. However, the issue remained after calibration.

I have also checked Max volumetric speed and even increased it slightly. Support print speed is already reduced by about 25% below the maximum allowed value, but this did not solve the issue either.

Another observation: the first layer of support may print normally, but on the following layers the right nozzle starts under-extruding again or almost does not extrude at all.

I am not using a Prime Tower because the printer has two nozzles, and the second nozzle is dedicated to support material. However, I now suspect that the issue may not be about purging/cleaning, but about the right auxiliary nozzle not building enough pressure after being idle before it starts printing support.

What has already been checked:

  • printing a separate test object with the right nozzle works normally;

  • manual Flow Dynamics Calibration for the right nozzle has been completed;

  • Max volumetric speed has been checked and slightly increased;

  • support speed has been reduced by about 25% below the maximum allowed value;

  • the issue appears specifically after switching from the main nozzle to the auxiliary nozzle;

  • the symptom looks like delayed pressure buildup/filament flow after idle time rather than constant under-extrusion.

Questions:

  1. How can I properly compensate for delayed extrusion on the X2D auxiliary/right nozzle after a tool change?

  2. Is there a setting for additional extrusion after tool change, such as Extra length on restart, Pre-extrusion, or Prime amount?

  3. Should I still use Prime Tower as a pressure-priming tower even though I am using two separate nozzles?

  4. Which retraction settings should I check for the auxiliary nozzle: Retraction length, Retraction speed, Deretraction speed?

  5. Could this be related to different right-nozzle temperatures after the first layer, such as Nozzle temperature - First layer vs Nozzle temperature -Other layers?

  6. Could this be caused by the right nozzle staying idle for too long between support sections and losing nozzle pressure?

  7. Does anyone have a working profile for printing Support Interface with the auxiliary/right nozzle on the X2D?

    You’re my only hope! I’ve already tried everything.

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The photo shows an example before flow calibration, but after calibration, the result remained the same.

To add: even if you print a model with the auxiliary nozzle and it turns out fine, the start of extrusion still has a delay, just like when switching the nozzle from left to right while printing supports.

2

This looks like pressure loss, not a flow calibration problem. The right nozzle sits idle too long. Pressure drops before support printing begins.

3

That’s right. The right nozzle always prints with a delay at the beginning of operation, regardless of the type of plastic or idle time, losing 10-20 mm of material at the start.

4

Two issues:

Having two nozzles doesn’t eliminate need for Prime tower, It doesn’t matter if you have 2 or 10 nozzles/hotends, you need a PRIME TOWER. It’s purpose is to build up pressure BEFORE it starts printing, eliminating the very issue you are facing. That back pressure in nozzle is lost when not in use. Instead of building that pressure on the tower, it’s doing it on your model, thus the issues you are seeing on your print. Having two or more nozzles eliminates purging, not the priming.

second.

You’ve performed the manual Pressure Advance (Flow Dynamic) and saved it, but are you actually LOADING the manual K-value?

The manual K-value profile you saved then needs to be assigned to the filament in either the Device/AMS tab or from the printer’s screen.

I know for the custom K-value to take effect on the main nozzle, you have to turn off Dynamic Flow when you send the print, not sure if same for AUX side.

You should see the value here once assigned.

Remember the Aux nozzle, the entire Dynamic flow or PA is a manual process in both calibrating for the value and then selecting the value.

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5

That is exactly the purpose of the prime tower: loading the nozzle again properly after it was idle. If you disable that, exactly that problem is to be expected.
And the amount of material for the prime tower is really not that much, even more so if your model only needs interface on a bunch of layers. The tower is printed quite smart.

If you really want to print without prime tower, I think there are some settings in the filament profiles for controlling how much filament is unretracted before starting the print. But even if you dial that in, it will never be perfect and either start printing air or ooze extra material that hangs somewhere on the model.

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6

Thank you, friends! I’m new to this, and you have helped me a lot.

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7

AHA!! That explains my question: why do we still have a prime tower when each nozzle only prints a single filament.

Thanks!