GRBL configuration
Walk through the GRBL settings that matter most for laser work. Set them once, write to EEPROM, move on.
For laser engraving on a GRBL machine, a small handful of $ settings determine whether the machine behaves correctly. This guide walks through them in priority order.
For the exhaustive list, see $ settings reference. For the underlying concepts, see GRBL essentials.
What you need
- The machine connected.
- The Console panel open.
Steps
1. Dump current settings
In the Console panel, send:
$$GRBL responds with every $ setting and its current value. Read them. Take a screenshot or save the output, useful baseline before changes.
2. Set laser mode
$32=1Enables laser mode. With dynamic-power M4 output, GRBL scales laser power with motion (lower during deceleration, full during cruise) so fills come out evenly. Required for dynamic-power engraving.
3. Set the max S value
$30=…The line is a template. Replace the ellipsis in $30=… with the controller's actual maximum S value; do not paste a line that still contains the ellipsis. Read the current $30 value from $$ and keep it unless the firmware documentation or machine manufacturer specifies a different value. Common values are 1000 and 255. The Device Settings S-value Max must match the controller.
4. Set max rates
$110=…
$111=…These template lines set the maximum travel speeds in mm/min for X and Y. Replace each ellipsis with a machine-specific value; do not paste the lines unchanged. Keep the current values or use manufacturer specifications until controlled motion testing justifies a change. Going beyond the machine's safe maximum can stall the motors or lose steps.
5. Set acceleration
$120=…
$121=…These template lines set the maximum accelerations in mm/sec² for X and Y. Replace each ellipsis with a machine-specific value; do not paste the lines unchanged. Keep the current values or start from manufacturer specifications, change them gradually, and verify that motion remains smooth without lost steps. Higher values mean tighter cornering but more stress on the mechanics.
6. Set steps/mm
$100=…
$101=…These template lines set the motor steps required to move 1 mm in X and Y and are specific to the motor / pulley / belt or leadscrew combination. Replace each ellipsis with a calculated value; do not paste the lines unchanged or copy a generic value. Keep the current values until you calculate replacements, then follow Steps per millimeter and verify the measured travel before relying on the result.
7. (Optional) Set up homing
If your machine has limit switches, enable homing:
$22=1
$23=…$22=1 enables homing. The $23=… line is a template: replace the ellipsis with the direction mask required by your machine, and do not paste the line unchanged. Keep the current $23 value unless the machine documentation or a controlled homing test shows that it is wrong. Test with clear travel, stay ready to stop the machine, and verify that each axis moves toward its intended limit switch.
8. Apply to Beam Bench profile
GRBL writes already persist in the controller's EEPROM. After changes, open Device Settings → GRBL Settings tab and click Apply to Active Profile to copy a valid $30 into S-value Max and the lower valid rate from $110 / $111 into Max Speed. It does not copy steps/mm, acceleration, homing, or every live setting.
Verify it worked
$$shows your new values.- A test rectangle cuts at the right size.
- A fill engraves uniformly (no banding at start / end).
- Jogging feels responsive but does not stall.
- If homing is enabled, each axis moves toward the intended switch and stops normally.
Common mistakes
- Dynamic-power setup mismatch: if engravings are noticeably darker / lighter at the start and end of each line, confirm
$32=1and that the active profile uses dynamicM4output with Constant Power (M3) off. $30mismatch: laser fires at the wrong intensity. Make sure Beam Bench's S-value Max matches.- Steps/mm wrong: cuts come out a percentage off. Re-measure and update.