PrusaSlicer: Set EM rate by file name (for Ellis' print tuning guide)

PrusaSlicer Set EM rate by file name.md

Set EM rates by file name

Summary

Ellis' Print Tuning Guide provides a great process for tuning Extrusion Multipler (EM), but I recently moved back to PrusaSlicer (RIP SuperSlicer) and I didn't want to print the objects one at a time (as suggested in the guide).

This script simplifies the process by automatically adjusting EM according to each file/object name.

How it works

PrusaSlicer's Verbose G-Code feature adds comments to the gcode file indicating the start/stop of each object. This script finds those comments and inserts a subsequent M221 command so that each object is printed with the correct EM.

For example, EM_Cube-1.000.stl prints at 100% EM, EM_Cube-0.995.stl prints at 99.5% EM (and so on...)

Installation

1. Install Python 3.x (tested with 3.11)
2. Download set_em_rates.py to a folder of your choosing

Instructions

1. Configure your slicer settings according to Ellis' guide
2. Enable the Output options -> Verbose G-code option
3. Add the the script to Output options -> Post-processing scripts:
   • Syntax: "[PATH_TO_PYTHON_EXE]" "[PATH_TO_SCRIPT]";
   • Example: "C:\Python311\python.exe" "C:\path\to\set_em_rates.py";
4. Add desired STLs from Ellis' labeld EM cubes
   • NOTE: Do not change the file/object names, otherwise the script will not work.
5. Slice and print as usual.

Compatibility

Tested with:

• Windows 11
• Python 3.11
• PrusaSlicer 2.7.1

Should also be compatiblie with different OS and versions of Python/PrusaSlicer, but I have not tested yet. Please leave a comment if it works for you.

Future development ideas?

• Customizable file prefix (instead of EM_Cube-)
• Option to customize other tuning options (temperature, retraction, pressure advance etc.)

set_em_rates.py

#!/usr/bin/python
import sys
import re
from pathlib import Path

# Filepath passed from PrusaSlicer
gcode_fp = Path(sys.argv[1])

# Define regex pattern for EM_Cube objects and extract em_rate to a named regex group
re_start_obj = re.compile("(^; printing object EM_Cube-(?P<em_rate>\d\.\d+).stl .+$)")

# Read g-code lines into list
with open(gcode_fp, "r") as f:
    old_lines = f.readlines()

# Build new list of lines, including our flow rate adjustments
new_lines = []
for line in old_lines:
    # Add line as-is to new_lines
    new_lines.append(line)
    # Adjust flow rate if starting a new EM_Cube
    match = re.search(re_start_obj, line)
    if match:
        # Convert decimal to percent
        new_em_rate = float(match.group("em_rate")) * 100  # percent
        new_lines.append(
            f"M221 S{new_em_rate} ; set_em_rates.py setting flow rate to {new_em_rate}"
        )

# Write changes to file
with open(gcode_fp, "w") as file:
    # file.write(new_content)
    file.writelines(new_lines)