GRBL mode¶

GRBL mode turns the machine into a standard Grbl-speaking laser cutter. This page tells you how to connect a sender, how the laser is armed and mapped, and what pausing, stopping, the lid, and the button do.

GRBL mode is the default mode and the one to use for your own designs (Modes). How the controller turns G-code into the pulse stream, and the state machine behind the behavior on this page, are in The grblHAL driver.

Connecting¶

The controller speaks Grbl 1.1 over TCP port 23. Point LightBurn, UGS, cncjs, or any Grbl sender at the machine's address on port 23. Setup details and a first job are in LightBurn.

Only one sender at a time is meaningful. Opening a second connection displaces the first. That is also why the web panel reads position from the machine's own counters and never from the Grbl socket.

A TCP disconnect never stops the controller process. A disconnect during a laser job holds the job where the cut stopped (see the table below). Jog from a sender's console with a standard jog command, for example $J=G91X40F1200.

GFSINK=/dev/glowforge grblHAL_glowforge -p 23 -e /data/forgefirm/EEPROM-glowforge.DAT

Laser mapping and power¶

• $32 (laser mode) is on by default, so M3/M4 and S behave the way senders expect. M4 gives dynamic power scaled with speed through acceleration ramps; M3 gives constant power.
• $30 is 1000, and S values map onto the laser drive with S1000 = full power. Set your sender's S-value maximum to 1000.
• A power change lands at exactly the point along the path where it was planned, whatever else the machine is doing.
• An S value commands a fraction of the light, not a fraction of the pulses: the controller maps it through a measured dose curve onto the pulse density that delivers it. Every power level marks, low levels included. LightBurn, Power explains the model as you meet it, and Settings lists the laser keys.
• $35, the power floor, is derived from the laser_floor_density setting at every job. Do not type it; the controller overwrites it.
• A change to a spindle $ setting takes effect when the controller restarts (a mode switch away and back, or a reboot). $$ reports the new value at once, but the mapping in force stays the one loaded at start.

Fire only ever rides motion segments of laser blocks. Rapids and homing are fire-free by construction, not by convention, and a jog is always shipped dark, even with the laser on and the button pressed: the Move panel never fires.

Arming: the button press is part of every job¶

The first laser-on of a job does not fire. Instead the machine checks that it is fit to cut, and then waits for you:

1. Is the cooling healthy? If the coolant is not proven to be moving, or is too warm or too cold, the machine refuses to arm and says so (Cooling and fans).
2. Is the print head there? No head, no arming: the lens, the air assist and the beam sensor all live on it.
3. The fans go to the cut profile, so every moment the beam can fire is covered by running fans and an active coolant check.
4. The button lights white and the job waits for your press. Your sender keeps getting status reports, so it will not time out.

The mechanism behind each step is on The grblHAL driver.

A press with the lid open does not arm the machine, and neither would the hardware latch clear on it. A soft reset, or opening the lid or the interlock, cancels the job instead. If nobody presses within laser_button_timeout_s (300 s by default), the job ends in alarm 3 with the laser locked again. The cooling is checked once more after your press, so the window can never open against a fault that appeared while the machine was waiting.

One press covers one job, not one cut. The window survives S changes and M5/M3 toggles, so nothing asks you again in the middle of a job. It closes, and the laser locks again, when:

• the job ends (M2, M30, %), the normal case;
• your sender disconnects or a different one connects, because the consent you gave belonged to that session;
• the laser has been off and idle for laser_disarm_s (60 s by default), which keeps counting while a job sits paused;
• anything goes wrong: an alarm, a homing cycle, a reset, or a stream fault.

The next job asks for a fresh press. That is the same press the machine's own hardware latch needs, which is why the software and the hardware can never disagree about whether the machine is armed.

Pausing, stopping, and faults¶

The controller clamps any feed faster than its limits: travels run up to 200 mm/s ($110/$111 = 12000 mm/min).

Lid, interlock, and button¶

ForgeFIRM reproduces the factory machine's behavior:

• A lid or interlock open during a job cancels it. Motion stops within milliseconds of the switch edge, the job is not resumable, the latch relocks, and the head returns to the position the job started from, with the lid still open, exactly as the factory does. The return-home move always runs to completion.
• The button pauses and resumes. In GRBL mode a press is a feed hold and the next press is a cycle start. A pause is not a cancel: the armed window stays open across it. A pause longer than the disarm grace closes the window; the next press then lights the button and re-arms before the job resumes.
• Idle lid cycles are ignored. Opening the lid to load material, or powering up with it open, does not leave the controller parked. Senders connect normally.
• Jogs are not lid-gated. A jog both starts and runs with the lid open; the beam is blocked in hardware regardless.
• Homing needs the lid closed. With homing_mode = gfcloud the cycle is a cloud homing session, and its move to the home corner is an ordinary motion action: refused with the lid open, and stopped if the lid opens partway through. The camera steps need the lid closed anyway. Only the lens hunt inside that session ignores the lid (Homing).

If you prefer stock Grbl door behavior, set lid_policy = hold (the GRBL tab): the job parks in the Door state, and a cycle start after the lid closes finishes the move with its position intact. The button still has to be pressed before the beam can return.

Homing, and running unhomed¶

The homing method is a setting, homing_mode, chosen in the web panel: gfcloud (camera homing through the Glowforge service), switches (the planned limit-switch cycle, not available), or none ($H is rejected). Homing has the procedure.

The machine cuts fine unhomed. Without a reference, coordinates are relative to wherever the head happened to be, so the panel shows position in red to say so, and your sender should use a job-start mode that does not depend on machine coordinates (LightBurn, Job start mode). After a successful home the position is anchored and shown normally.

Anything that invalidates position drops the reference deliberately, so a stale origin can never be reused (Homing).

Fans¶

In GRBL mode the cut fan profile follows your sender's M8/M9 (LightBurn's per-layer Air Assist), OR'd with the armed window: while the laser is armed the fans run the cut profile whatever the sender says (Cooling and fans).