Tuning Linear Advance to Eliminate Bulging Corners on a Bambu Lab A1

September 18, 2026 · by Tim Keller · 6 min read

Tuning Linear Advance to Eliminate Bulging Corners on a Bambu Lab A1

If you’ve printed anything with sharp corners on an A1, you’ve probably seen it: that little rounded blob where two walls meet instead of a crisp point. It’s one of the most common complaints on fast printers, and the cause is almost always nozzle pressure. When the print head slows for a corner, the hotend keeps pushing molten filament out for a split second longer than it should, and that excess plastic oozes into a bulge. Linear advance (Klipper calls it pressure advance) fixes this by predicting the pressure spike ahead of time and pulling back extrusion before the corner ever arrives. This guide covers how it actually works, how the A1 handles it, and how to tune it so corners come out sharp and dimensionally accurate.

Why Corners Bulge in the First Place

You can’t tune something well if you don’t understand why it’s happening. Filament sitting inside the hotend is slightly compressible, and it behaves a lot like a spring under load:

• Pressure builds up as the extruder feeds filament during a straight, steady-speed move.
• At a corner, the head decelerates, stops for a moment, then accelerates off in a new direction.
• Extrusion lags behind because the nozzle doesn’t shut off instantly. That lag dumps a small blob right at the corner.
• Sharp turns make it worse. A tight 90-degree corner shows the most bulging, while a gentle curve barely shows any at all.

The end result is a corner that looks swollen, sometimes with a visible seam or a little “ear” of extra plastic hanging off it. On functional parts that need to press-fit or mate with another piece, this isn’t just cosmetic, it throws off your tolerances.

Linear Advance vs. Pressure Advance: Same Idea, Different Names

Every firmware ecosystem seems to have invented its own name for this compensation trick:

• Linear advance (Marlin): controlled by the K factor.
• Pressure advance (Klipper): also a K value, but usually on a larger numeric scale than Marlin’s.
• Bambu Lab / OrcaSlicer: calls it “flow dynamics calibration” and stores it per filament rather than globally.

Whatever the name, the printer is estimating pressure inside the nozzle and adjusting extrusion before a speed change hits, not after. Dial the K value too low and corners stay bulgy. Push it too high and you overcorrect, leaving a visible gap or a starved, under-extruded spot right where the corner turns.

How the Bambu Lab A1 Handles Linear Advance

Good news: you don’t need to flash custom firmware or hand-edit G-code on this machine. The A1 gives you two routes.

1. Automatic flow dynamics calibration. The toolhead has an eddy current sensor that measures nozzle pressure directly. Enable “Flow Dynamics Calibration” in the slicer before a print, and the A1 runs a quick test on the purge line to set a starting K value on its own.
2. Manual tuning. For genuinely sharp corners, most experienced users skip relying solely on the automatic pass and instead run OrcaSlicer’s pressure advance test to nail down a K value per filament.

Automatic calibration gives you a decent average, but it’s just that, an average across conditions. Manual tuning almost always produces visibly cleaner corners, and the difference is especially obvious with PLA, PETG, and TPU.

Step-by-Step: Tuning Linear Advance on the A1

Step 1: Set a clean baseline

Before you even think about K values, make sure the rest of the printer isn’t lying to you:

• Run a full flow rate calibration (also called flow dynamics) so your extrusion width is actually correct.
• Dry your filament. Damp PLA or PETG makes pressure behavior jump around unpredictably, and you’ll end up chasing noise instead of a real number.
• Keep nozzle temperature consistent throughout the test. Even a 10°C swing changes viscosity enough to shift the ideal K value.

Step 2: Run the pressure advance test in OrcaSlicer

OrcaSlicer has a built-in pressure advance test pattern, which beats generating a test tower by hand any day:

1. Open OrcaSlicer and select your A1 printer profile.
2. Click Calibration in the top toolbar.
3. Choose Pressure Advance, then pick either the Line test (fast, easy to read at a glance) or the Pattern test (slower, but more precise).
4. Set a K range appropriate for a direct-drive printer, typically 0.0 to 0.05, stepping up by something small like 0.005 each time.
5. Slice it and print. You’ll get several segments in a row, each printed at a different K value.

Step 3: Read the results

Grab a bright light or your phone’s flashlight and look closely at the line segments. You’re hunting for the one where:

• The line stays a uniform width with no bulge at either end of the segment.
• Corners come out crisp, no blob, no thin gap either.
• The transition from the flat line to the raised edge looks clean and even.

Whatever K value is printed next to that segment is your target. If two neighboring values look basically identical under the light, pick the lower one. A slightly under-corrected corner is easy to clean up with a hobby knife; a gap from overcorrection is a much bigger headache.

Step 4: Enter the K value per filament

In OrcaSlicer, head to Filament Settings → Filament Overrides (Advanced) and type your measured value into the Pressure advance field. Save it as a named profile tied to that specific material. PLA, PETG, and TPU behave differently enough that a single global K value just won’t cut it.

Settings That Also Affect Corner Quality

Linear advance is one piece of the puzzle, not the whole thing. Check these too:

• Flow rate / extrusion multiplier. Over-extrusion will bulge corners even with a perfectly dialed-in K value.
• Outer wall speed. Slowing down to around 60-100 mm/s on outer walls gives the system less pressure to fight in the first place.
• Acceleration and jerk. Lower values at sharp corners buy pressure advance a bit more time to actually compensate.
• Nozzle temperature. Hotter filament runs thinner and is harder to control precisely at a corner. Use the lowest temperature that still prints reliably.
• Pressure advance for flexible filaments. TPU and TPE often need a noticeably higher K value paired with slower print speeds, since the material itself compresses more.

Common Mistakes to Avoid

• Copying K values from another printer. A Marlin K of 0.1, or a number pulled from a Klipper machine, won’t translate to the A1’s much smaller direct-drive range.
• Tuning with wet filament. You’re aiming at a target that keeps moving.
• Skipping flow calibration. If your flow rate is off, no amount of K tweaking will fix the corners.
• Treating all filaments the same. PLA, PETG, and TPU each need their own dedicated profile, full stop.

Conclusion

Tuning linear advance on a Bambu Lab A1 is probably the single biggest lever you can pull to kill bulging corners and get your parts back to their actual dimensions. Start with the A1’s automatic flow dynamics calibration as a rough baseline, then run the OrcaSlicer pressure advance test to lock in a proper per-filament K value. Pair that with correct flow rate, sane outer-wall speeds, and dry filament, and those round, blobby corners turn into edges that actually look, and measure, the way they’re supposed to.