We've been thinking about pressure advance compensation wrongly #860

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MrUnknownDE · 2026-04-05T16:33:27+02:00

MrUnknownDE commented

2026-04-05 16:33:27 +02:00

Originally created by @Wegerich on 2/7/2026

Is there an existing issue for this feature request?

I have searched the existing issues

I checked the existing issues and there were a few that were asking for features that would make a bandage for their problems: they are having problems with pressure advance, even though adaptive pressure advance is calibrated. I've realised that a change in the way that we do PA compensation would probably be able to fix all of these problems without needing a dozen new settings.

I've been thinking about pressure advance a lot, because it makes a huge difference for printing PETG which seems to be a bit stickier than other filaments and therefore incorrect PA can ruin the first layer completely, as perimeters don't start extruding until 20mm into the line and don't start adhering for another 10mm after that, so they peel off the bed and stick to the extruder.

After I've spent so many hours calibrating PA, how can this be?

Extruder internal pressure fluctuates according to according to volumetric acceleration, and speed, not linear acceleration and speed.

For example, here are two identical testing prints with identical acceleration values and identical flow rate, therefore they should have the same Pressure Advance setting, right?

It's probably quite clear to see that the pressure buildup in the print on the right would be much more gradual, and much less pressure advance compensation is needed.

But I believe that the way we're designing Adaptive Pressure Advance is based only on linear acceleration, not volumetric acceleration, so there are many cases where different line-widths and layer heights cause well calibrated PA settings to fall short and result in gaps at seams.

Which printers will be beneficial to this feature?

All

Describe the solution you'd like

I think the first thing would be to add a "Volumetric acceleration" statistic to accompany the "volumetric flow rate" in the info box in the layer examiner:

Longer term, I suppose that the Adaptive Pressure Advance feature would need to be redesigned so that it accounts for this and a new calibration pattern would be beneficial.

Describe alternatives you've considered

I'm not sure. I'd really like some feedback on this theory, especially if you think it might be the explanation for my terrible first layer adhesion with PETG on PEI! I've spent around 50 hours trying to dial in the settings and pretty much all I can do is have a really slow accelerating first layer so that it ignores the PA settings for all other layer types.

Additional context

No response

*Originally created by @Wegerich on 2/7/2026* ### Is there an existing issue for this feature request? - [x] I have searched the existing issues ### Is your feature request related to a problem? I checked the existing issues and there were a few that were asking for features that would make a bandage for their problems: they are having problems with pressure advance, even though adaptive pressure advance is calibrated. I've realised that a change in the way that we do PA compensation would probably be able to fix **all** of these problems without needing a dozen new settings. I've been thinking about pressure advance a lot, because it makes a huge difference for printing PETG which seems to be a bit stickier than other filaments and therefore incorrect PA can ruin the first layer completely, as perimeters don't start extruding until 20mm into the line and don't start adhering for another 10mm after that, so they peel off the bed and stick to the extruder. After I've spent so many hours calibrating PA, how can this be? **Extruder internal pressure fluctuates according to according to **volumetric** acceleration,** and speed, not _linear_ acceleration and speed. For example, here are two identical testing prints with identical acceleration values and identical flow rate, therefore they should have the same Pressure Advance setting, right? <img width="1708" height="1026" alt="Image" src="https://github.com/user-attachments/assets/2c5b52ce-3f9b-4880-b87f-98c98e2ca522" /> It's probably quite clear to see that the pressure buildup in the print on the right would be much more gradual, and much less pressure advance compensation is needed. But I believe that the way we're designing Adaptive Pressure Advance is based only on linear acceleration, not volumetric acceleration, so there are many cases where different line-widths and layer heights cause well calibrated PA settings to fall short and result in gaps at seams. ### Which printers will be beneficial to this feature? All ### Describe the solution you'd like I think the first thing would be to add a "Volumetric acceleration" statistic to accompany the "volumetric flow rate" in the info box in the layer examiner: <img width="435" height="423" alt="Image" src="https://github.com/user-attachments/assets/b997309a-d856-4637-8bba-74e5b4cd9c97" /> Longer term, I suppose that the Adaptive Pressure Advance feature would need to be redesigned so that it accounts for this and a new calibration pattern would be beneficial. ### Describe alternatives you've considered I'm not sure. I'd really like some feedback on this theory, especially if you think it might be the explanation for my terrible first layer adhesion with PETG on PEI! I've spent around 50 hours trying to dial in the settings and pretty much all I can do is have a really slow accelerating first layer so that it ignores the PA settings for all other layer types. ### Additional context _No response_

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Reference: github/OrcaSlicer#860