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LaserGRBL Setup Guide for Diode Lasers (2026)
LaserGRBL is free, open-source, Windows-only software that connects to any GRBL-based diode laser at 115,200 baud. The critical first step — before any engraving — is to open the console and send $32=1. Without it, the controller holds the laser at constant power through every corner and direction change, burning dark spots into every edge. Setup takes about 10 minutes. Last verified: 2026-07-07 — lasertinkerer.com
$32=1is the single most important setting — it enables M4 variable-power mode so corners don't over-burn- LaserGRBL is Windows-only; Mac/Linux users need LightBurn or xTool Creative Space
- Connect at 115,200 baud (not 9,600) — garbage characters at connect = wrong baud rate
- Power percentage maps to S-values: LaserGRBL 100% = S1000 (confirm
$30=1000in firmware) - Line distance controls DPI: 0.1 mm ≈ 254 DPI, 0.05 mm ≈ 508 DPI
- LaserGRBL works best for raster engraving; LightBurn is stronger for cutting complex vector shapes
$32=1 — is where most first-time burn problems originate. It takes ten seconds and is done once per machine.Step 1 — Download and Install LaserGRBL
LaserGRBL is developed by Mario Tonti and available for free on GitHub (search for mariotto/LaserGRBL). Download the latest release installer for Windows — there is no Mac or Linux version. The installer is small (a few MB) and requires no admin rights on most systems.
LaserGRBL requires Windows 7 or later with .NET Framework 4.x installed (pre-installed on Windows 8 and later). If the program fails to start on an older Windows PC, install the .NET Framework from Microsoft's site.
Step 2 — Connect to Your Laser at 115,200 Baud
Plug your laser into the computer via USB. The machine installs a USB-to-serial adapter driver — this is what creates the COM port LaserGRBL uses. If Windows doesn't install the driver automatically, your machine's manual will point to the right driver (usually CH340 or CP210x).
In the LaserGRBL connection bar at the top of the screen:
- Select the COM port your laser is on. If you aren't sure which one, unplug the USB cable, check the list, then plug it back in — the port that appears is your laser.
- Set the baud rate to 115,200. This is the standard GRBL rate. Older machines occasionally use 9,600 — if you see garbage characters or no response after connecting, try 9,600.
- Click Connect (the plug icon). GRBL responds with a version string in the terminal pane — something like
Grbl 1.1h ['$' for help]. If you see nothing or garbage text, the baud rate is wrong.
Once connected, type $$ and press Enter in the terminal pane. GRBL prints all its current parameter settings — this is your starting-point reference before you change anything.
Step 3 — Enable Laser Mode: $32=1 (the Most Important Step)
In the LaserGRBL terminal pane, type $32=1 and press Enter. GRBL replies with ok. This setting is saved in the controller's non-volatile memory — you only do it once per machine, not once per session.
$32=1Why this matters: M3 vs M4 mode
Without $32=1, the GRBL controller uses M3 mode — constant spindle power, regardless of head speed. When the laser head decelerates into a corner or changes direction, it slows down but the laser stays at whatever power level you requested. The result: the beam dwells at a corner and burns a dark spot. Every direction change gets the same treatment.
With $32=1 enabled, GRBL switches to M4 mode — variable laser power. Power scales proportionally with actual head speed relative to commanded speed. When the head slows for a corner, the laser power drops automatically to maintain consistent energy delivery per millimetre. Corners stay clean.
The diagram applies to LaserGRBL, LightBurn, and any other GRBL software — $32 is a firmware setting, not a software setting. It persists until you change it.
Step 4 — Verify Your S-Value Maximum ($30)
Type $30 in the terminal and press Enter. GRBL shows the current S-value maximum — the number that represents 100% laser power. Most modern machines ship with $30=1000. Some older or budget machines use $30=255.
LaserGRBL's power percentage always maps to your $30 value. If $30=1000, setting 80% in LaserGRBL sends S800. If $30=255, 80% sends S204. Either works internally — the key is to know which you have so you understand what "100%" means on your machine.
If your firmware shows $30=255 and you want to standardise to 1000 (recommended — it gives finer power resolution), send:
$30=1000| Parameter | Recommended | What it does | Symptom when wrong |
|---|---|---|---|
$32 |
1 | Laser mode — enables M4 variable power, makes power changes instantaneous | Dark spots at every corner; images stutter; full power on slow moves |
$30 |
1000 | S-value maximum — defines what S1000 means (100% power) | If set to 255 while software expects 1000: true max power is ~25%; faint engraving |
$31 |
0 | S-value minimum — laser power floor during moves | If >0: laser never fully off during travel moves; faint scorch lines between elements |
$13 |
0 | Report position in mm (not inches) | Position values appear 25.4× too large; coordinate confusion if you use G54 offsets |
Step 5 — Import an Image and Run Your First Engrave
With firmware configured, open an image file — LaserGRBL accepts PNG, BMP, and JPG. An import dialog appears where you configure the job settings. Here is what each option means:
| Setting | What it controls | Starting point |
|---|---|---|
| Line distance | Spacing between horizontal scan lines (mm) — lower = higher DPI, slower | 0.1 mm (254 DPI) for wood/leather; 0.05 mm (508 DPI) for photo work |
| Engrave direction | Unidirectional (one direction only) or bidirectional (back-and-forth) | Bidirectional for speed; unidirectional if you see horizontal shift on alternating lines |
| Speed | Head travel speed in mm/min | Check our settings database for your material. Start with a test grid. |
| Max power | Laser power at full dark areas of the image, as % of S-max | Check settings database. For basswood engrave at 10W: ~65% |
| Passes | How many times to repeat the job | 1 for engraving; 2–3 for thin cutting work |
| Dithering | Algorithm for converting grayscale to black/white dot patterns | Jarvis for wood; Floyd-Steinberg for photos; try both and compare on test material |
Which dithering algorithm to use
Dithering converts a grayscale image into a pattern of dots — the laser can only be on or off at any given point, so dithering simulates shades of grey. LaserGRBL includes several algorithms:
- Jarvis: Good general-purpose choice for wood and leather. Produces a balanced, fine-grained dot pattern. Start here.
- Floyd-Steinberg: Strong on photographic detail; can show more contrast in midtones. Try this for portrait photos on wood.
- Newsprint: Produces a halftone dot pattern that looks intentionally printed. Good for flat-toned artwork; not ideal for photos.
- No dithering (threshold): Hard black-and-white cutoff — good for logos and high-contrast line art, not for photos.
The right choice depends on your material and the image content. Run a small test crop with each algorithm before committing to a full project — see the DPI and image quality guide for a deeper comparison.
Before you burn: do a framing pass
LaserGRBL can trace the bounding box of your design at very low power before engraving. Use this to confirm the job will fit on your material. Look for a "frame" or "border" option before starting the job, or run the machine at 1% power to trace the outline manually. Never skip this on small or expensive material.
Always use OD7 safety glasses rated for 450nm whenever the laser is powered. Indirect reflections from metal fixtures or the honeycomb bed are enough to cause permanent eye damage.
Common LaserGRBL Problems and Fixes
| Symptom | Most likely cause | Fix |
|---|---|---|
| Garbage text on connect | Wrong baud rate | Try 115,200 first; if still garbled, try 9,600 |
| No response on connect | Wrong COM port or driver not installed | Unplug/replug USB; watch Device Manager for new port; install CH340 or CP210x driver |
| Dark spots at every corner | $32=0 (laser mode off) |
Send $32=1 in console |
| Engraving too faint even at 100% | $30=255 while software expects 1000 |
Send $30=1000 to raise S-max range |
| Faint scorch lines between elements | $31>0 — laser has a power floor during travel |
Send $31=0 |
| Image is horizontally shifted on alternating lines | Mechanical backlash in belt/carriage | Switch to unidirectional scanning; or calibrate backlash in LaserGRBL Options → Backlash |
| Machine moves but laser doesn't fire | $32=0, or S-value not in output, or safety stop active |
Check $32=1; check console for error codes; confirm door/lid switch not active |
| Job runs faster than expected, misses steps | Speed exceeds $110/$111 axis limits |
Reduce speed or raise firmware speed limits ($110=X max mm/min, $111=Y max mm/min) |
Frequently Asked Questions
Is LaserGRBL free?
Yes — completely free and open-source (MIT licence). Developed by Mario Tonti. No paid tier, no subscription, no watermarks. The only cost is time to set it up.
Does LaserGRBL work on Mac?
No. LaserGRBL is Windows-only. Mac users should use LightBurn ($99 one-time, 30-day free trial) or — for xTool machines — xTool Creative Space (free). Both support macOS natively and offer comparable or better features.
What does $32=1 do exactly?
$32=1 enables GRBL laser mode. Without it, GRBL uses M3 (constant spindle speed) — the laser stays at your requested power even as the head decelerates through corners, causing over-burning wherever the machine slows. With $32=1, GRBL uses M4 (variable power): laser power scales proportionally with actual head speed, keeping energy delivered per millimetre consistent. The setting lives in the controller's EEPROM — it applies to all software (LaserGRBL, LightBurn, etc.) and persists through power cycles.
What is line distance in LaserGRBL?
Line distance is the spacing between horizontal raster scan lines, in millimetres. Lower values = more lines per unit = higher effective DPI. Common starting points: 0.1 mm ≈ 254 DPI for wood and leather; 0.07 mm ≈ 360 DPI for moderate detail; 0.05 mm ≈ 508 DPI for fine detail and photos. Finer settings dramatically increase job time. See the DPI guide for a full breakdown.
LaserGRBL or LightBurn — which should I use?
Use LaserGRBL if: you're on Windows, you want free software, you mainly do raster photo/image engraving, and you don't need design tools or precise cutting. Use LightBurn if: you're on Mac or Linux, you need vector cutting, you want layers and a proper design interface, or you do rotary engraving. Both use the same GRBL firmware — firmware settings like $32=1 apply equally. Full comparison: LaserGRBL vs LightBurn.
Why is my engraving too light even at 100% power?
Check $30 in the console. If it shows $30=255 but LaserGRBL is using an S-scale of 0–1000, 100% in the software sends S1000 — but the controller treats anything above S255 as clamped to 255, which is only 100% of a 255-range scale. In practice this might work correctly, but if you suspect a calibration issue, standardise both to $30=1000. Other causes: focus too high, material needs more passes, or lens needs cleaning.
Gear for Getting Started
A few items worth having before your first burn:
- OD7 safety glasses for 450nm — required any time the laser is powered. Do not substitute cheaper glasses; OD4 is not adequate for a direct or reflected beam from a 10W+ module.
- Honeycomb work bed — elevates material off the base plate, prevents back-reflection, and provides clearance for smoke to escape. Makes cutting significantly cleaner.
- Air assist pump — directs a flow of air at the cut point to blow away smoke and combustion gases. Measurably improves cut depth and reduces scorch on wood and MDF.
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