3D printer bed mesh ignored — G-code & Linear Advance (K-factor/Pressure Advance)

Hey! We’ll make sure your bed mesh leveling actually applies during the print. Quick scan:
• Firmware: Marlin or Klipper? (printer model/board helps)
• Do you run Linear Advance (M900 K) or Klipper Pressure Advance? Current K-value?
• What’s in your start G-code? (G28, G29, M420 S1, BED_MESH_PROFILE LOAD, etc.)
• Symptoms: first layer fine at center but bad at corners, mesh works on test move but not while printing, Z offset changes when K is on, or ABL is disabled after homing?

You’re right: Linear Advance is an extrusion timing model (E vs F) and doesn’t directly move Z. But a few things make it look like the mesh is ignored:
1) M420 state resets after homing or some macros — if your slicer or firmware re-homes (G28) later, the mesh turns off unless you send M420 S1 (or RESTORE_LEVELING_AFTER_G28 is compiled).
2) Start G-code order: G29 after heating, then M420, then Z offset; wrong order can wipe the mesh or override ZBabystep.
3) Junction deviation/acceleration + M900 change extrusion pressure so first-layer line width shifts, masking compensation. Looks like Z error but it’s actually flow/line width.
4) Relative E + linear advance on some Marlin builds can cause early/late pressure ramps during the skirt/prime line; adhesion fails before mesh helps.

Let’s tighten the sequence. Recommended for Marlin + ABL/UBL:
G90 ; absolute XYZ
M82 ; absolute E (or M83 if you prefer relative)
M104 S{first_layer_temperature} ; preheat hotend
M140 S{bed_temp} ; preheat bed
G28 ; home all axes
M190 S{bed_temp} ; stabilize bed before probing
G29 ; build mesh (or M420 S1 if you store mesh)
M420 S1 ; ensure bed leveling ON
M900 K0.14 ; linear advance K
M109 S{first_layer_temperature}
G92 E0 ; reset extruder
G1 Z2 F6000 ; safe lift
G1 X2 Y10 F6000 ; move to prime
G1 E6 F300 ; prime
G1 X120 E15 F1200 ; prime line
Key ideas: heat the bed before G29 (thermal expansion), explicitly re-enable leveling with M420 S1, then apply M900. If you store a mesh in EEPROM, you can skip G29 and just call M420 S1.

Good call. Do this quick triage:
• Disable M900 for a single first-layer test and tune Z offset (paper test + live babystep). Store with M851 Z-0.xx then M500.
• Print a bed mesh validation (5×5 squares) with constant speed/flow. If all squares are even without M900 but vary with M900, it’s a flow/line width artifact, not Z motion.
• In slicer, set First Layer Flow = 100–105%, line width = nozzle × 120%, speed 20–30 mm/s. Too narrow lines exaggerate “ignored mesh”.
• If you use Relative E (M83), keep it consistent in start G-code to avoid pressure ramps mid-layer.

For Klipper:
• Ensure your start macro calls BED_MESH_CLEAR then BED_MESH_PROFILE LOAD=default (or BED_MESH_CALIBRATE).
• If you home after loading the mesh, Klipper still keeps it, but some macros (like adaptive bed mesh) may reload; check the order.
• Add QUAD_GANTRY_LEVEL / Z_TILT_ADJUST before loading the mesh.
• Pressure Advance in Klipper is orthogonal to Z; if your first layer only stabilizes on layer 2, increase first-layer extrusion multiplier or reduce PA on first layer: SET_PRESSURE_ADVANCE ADVANCE=0.03 at layer 0 via a slicer conditional, then restore at layer 2.

After a cancel, many printers reset leveling state. Add this to your start G-code so it’s bulletproof:
• Marlin: M420 S1 (or G29 A for UBL) after the last G28 and before the prime line. Compile with RESTORE_LEVELING_AFTER_G28 if available. Store mesh with M500.
• Klipper: explicit BED_MESH_PROFILE LOAD=default inside your PRINT_START macro and avoid re-homing afterward. Check that your cancel macro doesn’t clear mesh.
• Always heat bed to target before probing or loading the mesh (thermal consistency).

Yes—use per-layer advance:
• Marlin: in “before layer change” G-code, set M900 K0.10 for layer 0–1 and M900 K0.14 from layer 2 onward.
• Klipper: use slicer triggers to send SET_PRESSURE_ADVANCE ADVANCE=0.03 for layer 0, then restore 0.045 from layer 2.
• Keep first-layer speed ≤ 30 mm/s, line width ≈ 120%, and slightly higher flow (102–105%). This preserves bed mesh effect while still benefiting from advance on upper layers.

If your bed is stable: store and reuse.
• Marlin: run G29 once, then M500. In start G-code use M420 S1 (UBL users: G29 L# + G29 A).
• Klipper: calibrate with BED_MESH_CALIBRATE, then BED_MESH_PROFILE SAVE=default. Start macro: BED_MESH_PROFILE LOAD=default.
Probe again when you change surfaces, nozzles, gantry, or after major maintenance.

Summary: When a bed mesh seems ignored with Linear/Pressure Advance, fix the start G-code order (heat bed → G28 → G29 or M420 S1 → enable advance → prime), ensure leveling state persists (M420 S1 or BED_MESH_PROFILE LOAD), and tame first-layer flow/line width/speed. Use per-layer K/PA so the first layer sticks while upper layers stay crisp. Need help editing your slicer template? Open the chat.