Pressure Advance for Carbon Fiber Nylon: Tuning Out Bulging Corners and Blobby Seams

You calibrated flow, the walls measure right, and the corners still bulge. A blob stacks up at the seam, the wall goes fat through the turn and then thin for a few millimetres after it. Most people chase that with a lower flow rate and end up with gappy top layers. The setting you actually want is pressure advance — linear advance, if you run Marlin.

What Pressure Advance Actually Does

When the toolhead slows for a corner, the nozzle keeps pushing plastic at the old pressure for a moment. That extra lands right where the corner is. Pressure advance tells the extruder to back off just before the deceleration and push extra just before the acceleration, so the pressure at the nozzle tip matches what the toolhead is doing.

On a direct-drive high-temp machine with a 0.6mm nozzle we usually land between 0.03 and 0.05 on carbon nylon. Bowden setups run far higher, up around 0.4 to 1.0. Use those as where to start looking, not a number to copy.

Tune It in the Right Order

PA comes after flow and before speed: rotation distance (or e-steps), then flow rate, then pressure advance, then input shaping and speed. Tune PA on a wet spool and you will fight it forever — moisture pop looks a lot like a PA error, and spool friction changes as it dries. Dry the spool first, tune at the temperature and layer height you actually print, and skip the draft profile you will never run again.

Reading the Test

OrcaSlicer and Klipper both have pressure advance calibration built in — a line method or a tower that steps the value up every few layers. Print it in the material you care about, not PLA. Then look at corners only.

Too low: bulged corners, a blob at the seam, a thin spot or small gap just after each corner. Too high: rounded corners, gouged or pinched edges, gaps at the start of a wall, and the tail end of a long straight move thinning out as the extruder catches up. Pick the value where the corner comes out square and wall thickness holds through the turn.

Two things techs miss. PA shifts with temperature and with acceleration — raise accel and an untuned value shows up twice as hard. And it is per spool, so a new brand in a new colour gets a quick 15-minute tower before it goes on a real part.

What PA Won't Fix

Fat walls everywhere are a flow problem. Ripples at regular intervals across the print are ringing — that is input shaping. If the top layer is gappy while corners bulge, undo the flow cut and tune PA instead.

What We Use

We tune on spools we keep dry and know feed evenly. TINMORRY PA6-CF is what sits in the machine for most PA towers, and IEMAI PA12-CF covers the drier-running high-temp jobs. Both product pages carry the tested settings we run off the bench.

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