Knowledge
Practical LightBurn guides, settings, testing workflows and troubleshooting — written for real workshop use.
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26 articles
Laser output flashes or cuts out during motion
Separate project, GRBL power-scaling, speed, connection and hardware causes when the beam appears only intermittently.
GRBL $#: laser work coordinates and saved positions
Read G54–G59, G28/G30 and G92 reports in a laser workflow without treating CNC-only PRB/TLO data as a LaserLearn feature.
GRBL $G: Reading the Parser State
`$G` reports the controller’s active G-code modal state and is useful when a line behaves differently than expected because of inherited units, distance or motion modes.
GRBL Error:20: Unsupported G-code, Device Type or M4
Error:20 often points to unsupported/invalid G-code. In LightBurn, common causes include the wrong device type or M4 being sent to firmware/configuration that does not support laser-mode behavior.
GRBL ALARM:8 and ALARM:9: Homing Failures
ALARM:8 commonly means a homing switch could not clear during pull-off; ALARM:9 means the expected switch was not found within the configured search distance.
GRBL ALARM:3: Reset During Motion
ALARM:3 indicates a reset occurred while motion was active. Because physical motion may have stopped between known steps, the machine position may no longer be trustworthy.
GRBL ALARM:1: Hard Limit Trigger Diagnosis
ALARM:1 means a hard-limit input triggered during motion; position is likely lost and the cause may be physical travel, switch/wiring behavior or electrical noise.
GRBL ALARM:2: A Full Soft-Limit Diagnosis
ALARM:2 means GRBL predicted a commanded target outside known travel. Common causes include placement/origin mode, incorrect travel configuration, rotary use and coordinate offsets.
GRBL error:N vs ALARM:N — Different Failure Classes
An `error:` usually means a received command/block was rejected, while `ALARM:` signals a controller safety/state condition that can lock motion and sometimes invalidate position.
GRBL $130–$132: Maximum Travel and Soft Limits
$130–$132 define the controller-known travel extents and directly affect soft-limit checks. They should describe verified machine geometry, not just the design size you want to run.
GRBL $120–$122: Acceleration and Motion Quality
Acceleration affects how quickly axes reach feed rate and how hard the machine changes direction; too aggressive values can cause ringing, lost steps or limit-like symptoms.
GRBL $110–$112: Maximum Axis Rates
$110–$112 cap axis movement speed. Values above what mechanics can sustain can cause missed steps; values below desired job speed limit real output.
GRBL $100–$102: Steps per Millimeter
$100–$102 calibrate commanded distance to physical motion. Wrong values cause scale errors; they are not normal tools for fixing origin or workspace placement.
GRBL $32 Laser Mode and LightBurn M4
$32=1 enables GRBL laser-mode behavior such as variable-power M4 support on suitable GRBL versions. A wrong device type or disabled laser mode can produce Error:20/M4 messages.
GRBL $30: Maximum S Value and Power Scaling
$30 defines the controller maximum spindle/laser command scale; LightBurn device settings must agree with the controller so percentage power maps predictably.
GRBL $10 Status Report Mask
$10 controls parts of classic GRBL status reporting. Its exact interpretation can differ in forks, so decode the active firmware rather than blindly copying a recommended number.
A Safe GRBL $$ Health Check for Laser Use
A useful health check reads settings as a system: laser mode, S range, limits, homing, motion calibration, rates, acceleration and max travel — without assuming one universal “correct” dump.
Decode GRBL Realtime Status: MPos, WPos, FS, Bf, Ov and Pn
A `<...>` status report is structured telemetry: machine state plus position, feed/spindle value, buffers, overrides, pins and other optional fields.
Reading the GRBL Startup Message and $I
The startup line and `$I` reveal firmware family/version/build clues that determine which LightBurn device behavior and commands are appropriate.
GRBL Homing Cycle: $22–$27 in Context
Homing is a sequence, not a single switch: enable state, direction mask, seek speed, locate speed, debounce and pull-off must work together.
GRBL Hard Limits: $21, Switches and False Triggers
$21 makes physical limit inputs an emergency stop source; a trigger can be a real collision risk or electrical noise, so ALARM:1 needs evidence.
GRBL Soft Limits: What $20 Actually Protects
$20 soft limits prevent commanded motion beyond the configured machine travel, but only when the controller has a trustworthy position reference.
GRBL Negative Workspace and Workspace Offsets
Some GRBL machines home at max travel and use negative machine coordinates across the bed; LightBurn must be configured consistently with that machine coordinate model.
GRBL Errors and Alarms: Read the Console Before You Unlock Anything
Treat GRBL alarm/error numbers as diagnostic messages and fix the cause instead of reflexively clearing the controller state.