Knowledge
Practical LightBurn guides, settings, testing workflows and troubleshooting — written for real workshop use.
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170 articles
F and S: Feed Rate and Laser/Spindle Command Scale
F sets feed context for controlled moves; S sets spindle/laser command value within the controller scale. S is not automatically a percentage unless mapped against the configured maximum.
M3/M4/M5: Laser Output State in GRBL G-code
M3/M4 enable output modes and M5 disables output. For GRBL lasers, M4 is associated with dynamic laser power when supported/configured.
G90/G91: Absolute vs Incremental Distance Mode
G90 interprets axis values as absolute positions; G91 interprets them as increments from the current position. The same line can move somewhere entirely different under the other mode.
G20/G21: Inches vs Millimeters
G20 and G21 establish control units for following coordinates/feed values. A unit mismatch can turn a safe-looking file into a massively oversized move.
G2/G3 Arcs: I/J Centers, R Radius and Plane
G2/G3 describe clockwise/counter-clockwise arcs. Arc interpretation depends on active plane and whether center offsets (I/J) or radius (R) are used.
G0 and G1: Rapid vs Linear Feed Motion
G0 is rapid/travel motion; G1 is controlled linear feed motion. On laser jobs the important question is also whether laser output is active during the move.
G-code Modal State: Why One Line Depends on Earlier Lines
Many G-code words remain active until replaced: units, distance mode, motion mode, feed and spindle/laser state. Reading an isolated line without modal context can be misleading.
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.
Custom Jigs for Repeatable Production
A jig turns placement into a repeatable coordinate relationship; reliable jigs depend on a fixed machine reference, consistent stock location and a stable LightBurn positioning workflow.