LightBurn¶

This page sets up LightBurn for a machine in GRBL mode and walks through the operating basics: job start mode, power, air assist, dry runs, and a good first job.

Jobs sent from LightBurn fire the laser. Safety has the rules that apply to every job. The operator-armed window that every firing job passes through is under GRBL mode.

One-time device setup¶

Prerequisite: the machine is in GRBL mode (Modes); the controller listens on TCP port 23 at your machine's address, shown below as <machine-ip>.

1. Laser window, Devices, Create Manually (skip auto-find; it scans serial ports).
2. Device type: grblHAL if your LightBurn version lists it, otherwise GRBL. Both speak the right protocol.
3. Connection: Ethernet/TCP. IP address: <machine-ip> (LightBurn uses TCP port 23 for GRBL devices, which is exactly where the controller listens).
4. Name: for example Glowforge ForgeFIRM. Work area: X 495 mm, Y 279 mm.
5. Origin: pick the corner where the head sits after parking at home: rear-left as you face the machine (the top-left dot in the selector). This is what keeps jobs un-mirrored: machine +X runs right, +Y runs from the rear rail toward you.
6. Auto-home on startup: NO. LightBurn would issue $H at every connect, and the camera homing method runs a session of a minute or more. $H itself works and is selected by the homing_mode setting in the machine's web control panel: gfcloud (Glowforge web-service vision homing; X/Y home to the factory corner, Z to the hall sensor; requires a signed-in Glowforge session), switches (physical limit switches, planned), or none ($H is rejected). Run $H deliberately from the Console tab when you want a true machine origin (Homing). Z is the focal point's height above the tray: a Z of 3 focuses on the top of 3 mm material, and the job's Z moves the lens. The lens never moves without a reference: before a home, any Z move is refused (a jog with an error, a job with the soft-limit alarm), and after one, a Z beyond the lens's free travel is refused the same way. The reach is on the control panel's Machine tab, under Lens.
7. Finish. If a stale device profile already exists, edit its IP instead of creating a new one.
8. Device Settings (wrench icon): S-Value Max = 1000 (matches $30).
9. Optional backup: File, Export Devices saves a .lbdev you can re-import later (the format is not editable text; export is the way to make one).

Job start mode¶

This matters on an unhomed machine. In the Laser window set Start From: Current Position, and set the Job Origin dot to the same corner as the machine origin (top-left dot). The job then runs into the bed from wherever the head currently sits. Absolute machine zero never matters, which is the forgiving mode when you have not homed.

Absolute Coords also works after a successful $H, or if the head was parked at the home corner when the controller started. After any Stop or alarm the absolute frame is stale until you re-home with $H or restart the controller with the head re-parked.

Operating basics¶

• Frame traces the job's bounding box at travel speed. Do it before every Start. There are no limit switches: framing is your crash protection.
• Start runs the job. Travels run up to 200 mm/s; anything faster in a layer is clamped by the controller ($110/$111 = 12000 mm/min).
• Pause = Grbl feed hold: motion parks within about 0.4 s (0.2 s stream queue plus deceleration); Resume continues exactly. The big button does the same: one press while a job runs pauses it (LightBurn shows Hold), the next press resumes it: the factory's pause and resume, on the machine. Two things to know before you pause a cut. Resume where it stopped: there is no backtrack in GRBL mode, so the beam restarts from where the deceleration ended and accelerates away from a standstill. At constant power (M3) that leaves a deeper spot you can see, while M4 scales power with speed and mostly hides it. Do not leave it paused: the armed window has an idle grace (laser_disarm_s, default 60 s) that counts down through a hold, so a job left paused disarms itself and the resume asks for the button again before it can fire.
• Opening the lid (or a Pro's interlock loop) during a job cancels it, as the factory firmware does: the head parks with a controlled deceleration (the hardware cut the beam the instant the lid moved), the console reports the reason, the job ends for LightBurn (the controller resets; position is kept, no alarm), and the head returns on its own to where the job started, lid open or not. Close the lid and start again from LightBurn; the next job asks for the button, which is also what re-arms the machine's hardware button latch. The lid_policy setting on the control panel's GRBL tab can select the stock Grbl behavior instead (Door hold, Resume once closed). At idle, while jogging, or during homing the lid is yours to open and close freely. The controller does nothing there (the hardware blocks the beam anyway), so a lid cycle while loading material never leaves LightBurn waiting.
• Stop = soft reset: motion aborts with a controlled deceleration and grblHAL raises an alarm with position declared lost (the stream queue means up to about 40 mm of in-flight difference). It leaves the head where it stopped. The return to the job start belongs to the lid and interlock policy alone, so Stop never moves the machine on its own. Recovery: unlock ($X in Console or LightBurn's prompt), jog the head clear, and carry on in Current Position mode. Restart the controller with the head re-parked if you want a clean absolute frame.
• Move tab: jogging (set a sane speed, for example 6000 mm/min), Get Position, distance buttons.
• Console tab: raw Grbl: ? status, $$ settings, $X unlock, $J=G91X10F1200 jog.

The camera¶

LightBurn can show the lid camera behind your design. Add it in LightBurn's camera setup as a custom camera with the stream URL from the panel: open the Status tab, press Camera URL on the lid camera card, and paste the stream line. It reads http://<machine-ip>/?action=stream&key=<key>, with no port. The key lets LightBurn read the camera without a login, whether or not the reads are closed to the network. The camera works only with the lid closed (Cameras).

Power¶

The controller drives the tube the way the factory does: every pulse fires at full power, and the power setting decides how many ticks of each 710 us period fire. Every power level marks, low levels included, because no pulse is ever too weak to strike. The raw response is not linear (80 % of the pulses deliver about half the light), so the controller maps your power setting through a measured dose curve: 50 % commands half the light, not half the pulses. The machine ships with a measured default curve; record your own tube's from the control panel (GRBL tab, "Dose-curve recorder": download the ladder file, press Record, run the file from LightBurn on scrap, press the button, Apply the fit). Grayscale images fade cleanly into the shadows (a low level becomes sparse full-power pulses), and 254 to 508 DPI rasters hold their tonal steps.

$35, the power floor, is set by the controller from the machine config (the control panel's GRBL tab, "Laser dose"): do not type it, it is overwritten at every job.

S-value scale: $30 defaults to 1000, so set LightBurn's S-max to 1000. 100 % power = S1000. Use M4 (variable/dynamic) mode for cuts and engraves.

Air assist and fans¶

Each cut or engrave layer has an Air Assist toggle (in the layer's cut settings). Turning it on makes LightBurn emit M8/M9 around that layer, which drives the machine's full cut-profile ventilation: air assist to full, exhaust and intake fans to factory run speeds, then a cooldown of about 15 s after the layer before returning to idle. Leave it ON for anything that will eventually involve the beam; expect real fan noise.

The machine forces the cut fan profile on while armed and continuously verifies coolant flow; a flow fault or over-temperature pauses or blocks firing, and the messages appear in LightBurn's console (Cooling and fans).

Dry runs (motion only, no fire)¶

Setting a low power value does NOT make a job inert. Any laser layer prompts for the arm button and then fires. The motion-only modes are:

• Frame and jogging: they never fire.
• A job whose layers emit no laser-on command: turn the layer's Output off in the cut settings, or send G-code that stays in M5.
• A job run with the laser latch left locked (never press the arm button): the job pauses at the white-button prompt and aborts after laser_button_timeout_s. Useful only to confirm the prompt itself.

If the white arm prompt appears and you did not intend to fire, press Stop in LightBurn.

A good first job¶

First a dry run, then a light cut on scrap:

1. Draw a rectangle (about 100 × 60 mm) with a circle inside.
2. Double-click the layer color bar (bottom): mode Line, speed 50 mm/s (= 3000 mm/min; check Edit, Settings for your speed units). For the dry run turn the layer's Output off.
3. Park the head where the job's rear-left corner should be (or leave it at home), Frame, watch the perimeter trace, then Start.

Expected behavior: darting travels at up to 200 mm/s, smooth 50 mm/s tracing of the shapes, silky and near-silent motion (factory currents and decay mode), and the head finishing per the job's return setting.

1. For the live pass: put scrap material on the bed (never an empty honeycomb over the fan grill), re-enable the layer's Output, set power to 20 % (any nonzero power marks; 20 % is a light pass on scrap), turn the layer's Air Assist on, close the lid, Frame, Start, and press the white button when it lights. Watch the whole job.