Glossary · Calibration

3D printing

Pressure advance (linear advance)

A function of the printer firmware that predicts the pressure in the nozzle. This makes corners sharper and the starts and ends of lines more even.

Explained in more detail

The filament between the drive and the nozzle behaves slightly like a spring. When the print head accelerates, the material arrives late; when it brakes, the material keeps pushing: corners bulge, line starts are thin and the seam becomes untidy. Pressure advance compensates for this by having the extruder feed slightly more during acceleration and slightly less during braking. The value, often called K, depends on the filament, temperature and extruder. According to the Klipper documentation it is usually between 0.05 and 1, with values at the upper end more likely on Bowden extruders. In Marlin the function is called linear advance, and in Bambu Lab it is called Flow Dynamics.

Where does the term come from?

The name describes the principle: the extruder anticipates the pressure needed. Klipper calls it pressure advance and Marlin calls it linear advance; at heart the same thing is meant.

In practice

• The value belongs in the filament profile; it does not apply to all materials.
• Many current printers measure the value automatically; Bambu Lab calls this Flow Dynamics Calibration.
• With Marlin, linear advance must be enabled in the firmware, which is not the case for every model.
• Blobs only at corners while straight stretches look good point to a value that is too low.
• Pressure advance and flow affect each other slightly. If the corners are no longer right after flow calibration, check pressure advance again.

Not to be confused

Pressure advance is not retraction: retraction pulls the filament back during travel moves, while pressure advance adjusts the feed during printing. According to Klipper, however, it also reduces oozing during travel moves.

Frequently asked questions

How do I find the right value?

With a calibration test in the slicer, for example in OrcaSlicer: it prints lines or a tower with increasing values, and you pick the spot with the cleanest corners. Klipper recommends taking the lower value if in doubt.

Do I have to retune pressure advance for every filament?

Yes, the value depends on the material, temperature and extruder and is stored in the filament profile. After changing the nozzle or extruder you should determine it again as well.