Older versions of Grbl do not have this feature, and simply run the laser at a constant power output for the duration of a cut. In this mode, Grbl adjusts the laser power as the machine speeds up and slows down, making for very consistent cutting and marking. The second is a feature called variable power mode, or the M4 command. Laser mode eliminates the pauses that happen when changing power output, because Grbl knows it's controlling a laser which reacts instantly, instead of waiting for a spindle to change RPM. The first is Laser Mode, enabled by setting $32=1 in the firmware settings.

The more recent versions of Grbl (1.1f and up) support two things that are incredibly useful for lasers. Luckily this is easy to change, and easy to switch from one to the other. The 'standard' way a CNC machine is configured is somewhat different from the way laser machines often are. It is highly configurable, and this is both a blessing and a curse. Grbl firmware was originally designed for CNC machines and 3D printers, with laser support added more recently.

If your machine does not have homing switches (also called limit switches) you will need to home it manually if you want to use Absolute Coords or User Origin modes.

Make sure the controller is reporting positions in mm, as expected by LightBurn ( $13=0).

Set your machine status reporting to be relative to the workspace origin, not the machine origin ( $10=0).

If your machine uses negative workspace coordinates you'll need to apply a workspace offset ( G10 L2 P1 xx yy).

The pause, which happens on older versions, or when not using Laser Mode, will cause excessive burn spots when engraving images.

If you have an older version of GRBL (prior to 1.1f) it's highly recommended to upgrade the firmware, as Laser Mode also prevents the machine from pausing with every power change.

You might need to enable 'Laser Mode' if you have GRBL 1.1f or later ( $32=1).

The value in LightBurn is called 'S-Value Max', in the Device Settings.

You might need to adjust your spindle max RPM value ( $30) to match the LightBurn default (1000) or vice versa.

If you have a GCode-based system, like a Shapeoko, Eleksmaker, X-Carve, or Acro system, you might need to make some simple changes to get the most from LightBurn.

Lightburn software control air assist