Step 14.9 — Close Ch 12's PRINT_START TODO with the purge line¶
Step 9 of 36 · Chapter 14 — Calibration and tuning
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Parts: none.
Do: PRINT_START is owned by Ch 12 Step 12.36; do not write a second one here. It ends with a ## TODO Ch 14: purge / prime line goes here marker. Now that the extruder is calibrated, replace that marker with:
G90
G1 X5 Y5 Z0.3 F6000 ; <-- 350 only
M83 ; relative extrusion for the purge
G92 E0
G1 X120 E20 F1200 ; purge line
G1 Z2 F600
Check
A hand-run PRINT_START CHAMBER=0 lays a continuous purge line at X5 to X120 that sticks, and grep -c '^\[gcode_macro PRINT_START\]' printer.cfg returns 1.
What you're looking at
A purge line is a short stripe of filament laid at the plate edge before the real print, to build nozzle pressure and wipe off ooze. It goes into Ch 12's PRINT_START macro rather than the slicer, so every print gets it.
M83 and G92 E0 are not optional. Klipper starts in absolute extrusion mode, and Ch 12's macro does not set M83/G92 E0 until after this point — a bare G1 E20 here would extrude to an arbitrary absolute position instead of 20 mm.
The slicer side already exists: the Voron 2.4 350 printer preset from Ch 13 calls PRINT_START BED=[first_layer_bed_temperature] EXTRUDER=[first_layer_temperature] CHAMBER=0 FILAMENT={filament_type[initial_tool]} and PRINT_END; nothing in the slicer changes for the purge line, because it lives in the macro.
Caution
Run it from the console with the machine cold and watch Ch 12's order: homes first, heats the bed, timed soak, QGL hot, re-homes Z, meshes, parks at X5 Y5, heats the nozzle, then purges. Send PRINT_END afterwards; the hand run leaves the heaters on otherwise.
Caution
Keep CHAMBER=0 until the previous step has told you what your chamber actually reaches. TEMPERATURE_WAIT has no timeout: a CHAMBER=50 the machine never reaches blocks the print forever, and the only way out is cancelling. Once 14.8 gives you a repeatable settled value, set CHAMBER a few degrees below it — never at or above it. src
Good stopping point · ~15 min since the last one
chamber behaviour measured and written down, and PRINT_START's Ch 12 TODO closed with the real purge line. CHAMBER is still set from a measured number, not a guess. Config restarts clean.
Source: leviathan-printer-rev-d-sbv2.cfg · Klipper docs § TEMPERATURE_WAIT