Pressure advance is the difference between corners that look clean and corners that show bulges or tiny gaps. The goal is simple: when your print head slows down or speeds up for a corner, pressure advance helps the extruder add or remove a little extra plastic so the line width stays consistent.
This guide walks you through an end-to-end calibration workflow: what to check in firmware and slicer, how to run a proper test, how to read the patterns to pick a value, and when you should re-run the calibration after changing nozzle or filament.
Know what pressure advance fixes (and what it doesn’t)
Corner-related defects that pressure advance can improve:
- Bulging at the start of a corner: the extruder momentarily pushes too much filament as the head enters the turn.
- Gaps or thin corners: the extruder momentarily pushes too little filament as the head completes the turn and resumes a different speed.
- Wavy, inconsistent line thickness near direction changes: the flow is “lagging” behind the commanded motion.
Defects pressure advance usually won’t fully fix:
- Bad first layer or poor bed adhesion (that’s leveling, bed temperature, and first-layer flow).
- Under-extrusion from incorrect flow/steps or too-low temperature (fix flow/temperature first).
- Loose belts, sloppy mechanics, or worn V-wheels (pressure advance can’t correct physical inaccuracies).
If you’re seeing corner issues, treat pressure advance as the final speed/flow compensation layer—but only after basic extrusion and motion health are in place.
Set up the firmware and slicer so you’re tuning the right thing
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Identify which pressure feature your firmware uses
- Marlin-style systems often use a K parameter (commonly changed via firmware settings or an M-code).
- Klipper-style systems use a pressure advance parameter (and may also have related timing or shaping features depending on configuration).
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Confirm where the value is set
- Prefer setting it in firmware/config, not in multiple places.
- If your slicer also offers pressure advance/linear advance fields, ensure you’re not overriding firmware with conflicting values.
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Freeze other variables for the test
Pressure advance is sensitive to how quickly material flows and how sticky it is. For a clean calibration, keep these steady:- Same nozzle diameter and extruder hardware.
- Same filament type (brand and formulation) and ideally the same spool.
- Same print profile: speeds, acceleration limits, and layer height.
- Same hotend and bed temps (don’t chase temperature changes while calibrating).
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Use a test run that actually stresses corners
The test should include multiple sharp direction changes at increasing extrusion rates or step changes in speed. If your “test” is just straight lines, you won’t get meaningful feedback.
Run an end-to-end pressure advance test
Here’s a practical workflow that minimizes confusion and makes it easy to interpret results.
- Start from a known-good print baseline
Print a quick rectangle or simple model to confirm you’re not dealing with obvious under/over-extrusion, stringing from bad retraction setup, or mechanical wobble. - Set an initial pressure advance value
Use your current K/pressure advance value if you have one. If not, start low (a value that produces under-compensation is usually easier to spot than one that causes aggressive bulging). - Pick a single speed/accel profile for the calibration
Use the exact speeds you normally print with (or the speeds you want your corners to look good at). Pressure advance isn’t universal across profiles. - Prepare the calibration model/G-code
Use a purpose-built pressure advance calibration print that includes corners/turns and is designed for incremental changes across sections. - Slice and generate G-code with retraction behavior consistent
Keep retraction enabled/disabled the way you normally print. Don’t change retraction during the calibration unless your firmware requires it for the calibration method. - Print the calibration with stable environmental conditions
Avoid drafts, and ensure the nozzle reaches steady temperature before starting. - Inspect the first range carefully
Look for the section where corner lines appear closest to the expected line width: no obvious bulge and no obvious thinning. - Adjust pressure advance and re-run
Change the value in small increments and reprint. Aim for fewer, more targeted runs rather than big jumps. - Record the final value with the profile details
Note the firmware parameter name (K/pressure_advance), nozzle type, filament, temps, speeds, and layer height so you can reproduce it later.
If you only do one calibration per filament or per profile, do it at the speed you care about most—because the “best” pressure advance is strongly tied to how fast you’re printing.
Read the calibration results and choose the best value
A good pressure advance calibration is really about recognizing patterns. As you increase pressure advance:
- Under-compensation often looks like thin corners or slight gaps where the line should be full.
- Over-compensation often looks like bulging corners or extra material at turns.
- The right value produces corners where the line width stays consistent and the transitions don’t show strong swelling or starving.
How to pick “the best” section:
- Prioritize corner quality over straight segments. Straight lines can look acceptable across a wide range of values because they don’t involve abrupt speed changes.
- Look at both sides of each corner (entry and exit). Some values overfill at entry but starve at exit. The ideal value minimizes both.
- Check consistency across multiple turns. If one corner looks perfect but neighboring sections are clearly wrong, that’s a hint you should refine around that value rather than locking it in.
Practical adjustment strategy:
- If you see consistent bulging at corners, reduce K/pressure advance.
- If you see consistent thin corners or gaps, increase it.
- If you see alternating over/under effects in adjacent sections, adjust more narrowly and re-run.
Re-run calibration when nozzle or material changes
Pressure advance is not a one-and-done number. Any change that affects melt flow, viscosity, or how pressure builds up in the nozzle can shift the optimal value.
Re-run pressure advance after:
- Changing nozzle diameter or type (even if the new nozzle is “the same size,” real flow behavior can differ).
- Switching filament type (PLA vs PETG vs ABS/ASA vs flexible filaments) or switching to a different brand/grade.
- Changing hotend temperature significantly (even within the recommended range, viscosity changes can matter).
- Changing your speed/acceleration profile (especially if you print faster than before).
When you change settings, follow this order to avoid chasing noise:
- Verify mechanics and extrusion health (extruder tension, nozzle cleanliness, steady temperature).
- Re-check flow/rotation calibration only if you changed hardware or temperatures so much that dimensional accuracy is clearly off.
- Then re-run pressure advance with the same new conditions you’ll actually use.
Finally, keep your notes consistent: pressure advance depends on your motion profile and material behavior, so the value you choose is only meaningful alongside the profile you used to get it.
Quick sanity checks to prevent false results
If the calibration “looks wrong” in a way that doesn’t match your expected bulge/thin behavior, check these before adjusting K again:
- Clogging or partial nozzle blockage: can mimic under-extrusion symptoms at corners.
- Inconsistent extrusion temperature: a fluctuating hotend can cause changing corner behavior during the test.
- Worn belts or excessive play: direction changes amplify any mechanical slop.
- Multiple firmware/slicer overrides: if two systems fight over flow timing, you’ll never find a stable best section.
Once these are solid, pressure advance becomes a controlled tuning problem rather than guesswork.
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