G-code postprocessing script to modify first layer travel speed

limit_first_layer_travel_speed.py

#!/usr/bin/env python3
# Copyright (c) 2022 Sean C. Monahan
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"""in Post-processing scripts, put:
{full-path-to-this-file} {your-desired-first-layer-travel-speed-in-mm-per-second}

(On Windows, I think it would be
{path-to-your-python-interpreter} {full-path-to-this-file} {your-desired-first-layer-travel-speed-in-mm-per-second}
)

This will modify the gcode output to change first layer travel moves to use the specified speed.
This is hacky as heck. It _should_ still work if you enable verbose gcode output.

This will probably break if the travel speed set in SuperSlicer itself is identical to any first layer
extrusion speeds (unlikely) because it will omit redundant G1 F parameters.

This could be refactored to be able to apply any transformer function to an arbitrary layer
"""

from sys import argv
from os import environ

import shutil

from tempfile import NamedTemporaryFile


def main(argv=argv):
    # note: G1 moves speeds are in mm per minute, so multiply by 60 seconds-per-minute
    travel_speed = 60 * int(environ["SLIC3R_TRAVEL_SPEED"])
    first_layer_travel_speed = 60 * int(argv[-2])
    input_gcode_filename = argv[-1]

    def adjust_speed_if_travel_move(line: str) -> str:
        # for matching purposes, strip whitespace and any comment
        trimmed = line.split(";", 1)[0].strip()

        if (
            (trimmed.startswith("G1 ") or trimmed.startswith("G0 "))
            and trimmed.endswith(f"F{travel_speed}")
            and ("Y" in trimmed or "X" in trimmed)
            and "E" not in trimmed
        ):
            return line.replace(f"F{travel_speed}", f"F{first_layer_travel_speed}")

        return line

    with NamedTemporaryFile(
        mode="w+t",
        prefix="limit_first_layer_travel_speed_output",
        delete=False,
    ) as output_gcode, open(input_gcode_filename) as input_gcode:
        output_gcode_filename = output_gcode.name

        # pass through unchanged all the lines until the first ';LAYER_CHANGE'
        for line in input_gcode:
            output_gcode.write(line)

            if line == ";LAYER_CHANGE\n":
                break

        # now we're in the first layer, until we hit the next ';LAYER_CHANGE'
        for line in input_gcode:
            output_gcode.write(adjust_speed_if_travel_move(line))

            if line == ";LAYER_CHANGE\n":
                break

        # pass the rest of the lines through unchanged
        for line in input_gcode:
            output_gcode.write(line)

        # add one final comment line stating that we rewrote first layer travel moves
        output_gcode.write(
            f"; first layer travel moves changed from {travel_speed} to {first_layer_travel_speed}\n"
        )

    # replace the original gcode file with our modified gcode
    shutil.move(output_gcode_filename, input_gcode_filename)


if __name__ == "__main__":
    main()

Thank you, very helpful!!