Manufacturers like to advertise high speed figures — e.g. 30,000 mm/min on the X and Y axes. These values are theoretically correct, but engraving is in reality rarely single-direction motion.
The Pythagorean relationship: if the machine moves diagonally (e.g. the diagonal of a 400×400 mm bed), the diagonal is 565.7 mm — 1.41 times the base length. The controller has to cover this faster direction too, which reduces the actual achievable speed.
So a "30,000 mm/min" machine actually can't move diagonally in a stable way above ~21,000 mm/min. This isn't a manufacturer's lie — it's just physics.
Relationship: acceleration values need to be proportional to the max rate. A smaller acceleration is recommended alongside a high speed — so the machine doesn't jerk, and the belt doesn't skip a tooth. On V-slot wheel systems, experience puts the safe upper limit at roughly 15,000 mm/min. On linear rail (HGR20) systems, this can be significantly higher.
The state of the mechanics reveals a lot through what you hear. As a beginner it's easy to take these sounds for granted — but each one has a cause.
The motor shaft is touching some metal part. Check the pulley's grub screw and the shaft's position.
Worn or dirty wheels. Clean them, then replace if needed.
Loose pulley or too much acceleration. Check the grub screw and reduce the $120/$121 values.
The motor can't keep up with the steps — too high a speed, a loose belt, or a dirty guide surface.
You don't need to dig into GRBL code to find the right speed values — LightBurn's console window is the perfect tool. First make a backup, or know that the $RST=$ command restores the default values.
Warning: the motors will move during the test below. Watch for sound and visual cues. If you feel unsure about your machine's condition, don't run the higher values.
Set the starting values in the LightBurn console:
Send the moving head to the corner opposite the homing position. Listen to and watch the motion — it should be smooth, without collision.
Send it home. If everything's fine, increase acceleration:
If you notice an error (clicking, skipped steps, whining), lower it:
Once you've found the right value, lower it by another 10–15%. This is the safety margin — so it keeps working stably even when hot or with a worn belt.
LightBurn macros: for the cutting and engraving values you find this way, it's worth creating separate macros in LightBurn — the optimal configuration for a given task can then be set with a single click.