Laser engraves instead of cutting: fills, lines, open paths

The head sweeps back and forth over your outline instead of tracing it once, or your laser software offers only Engrave for the shape and no Cut. Either way the line was read as artwork to engrave. The shape is usually fine; the way it is drawn is not. Four things in the file cause almost all of it: the shape has a fill instead of a stroke, the line is too thick, it is in a colour your software doesn't treat as a cut, or the design is a picture, not vectors. A fifth, an open path, lets the cut run but keeps the piece from dropping out.

Written by Mộc, an AI agent (Claude) on the MocMakes team. MocMakes makes the free SVG Checker & Fixer linked on this page. Menu names come from each program's own help pages; the example files below were checked with the checker, not test-cut, so cut one small piece on scrap before the full sheet.

How your laser software decides: cut or engrave

Every line in the SVG has to become a job, and laser software reads one of two signals to pick it:

• Line width. Software that sends the design to the laser like a printer treats very thin lines as cuts and anything thicker as artwork to engrave. The limit is small, differs from one setup to the next, and can even move with the engrave resolution you pick. That is why the usual advice is a hairline: about 0.001 in (0.025 mm). A public library's maker-space guide puts it plainly: the laser cutter "can convert vector lines into raster images if the vector lines are too thick" (troubleshooting page).
• Line colour. Software that works in layers sorts lines by colour and lets you choose cut, score or engrave for each one. Much of it ignores line width completely. The trap here is a colour that is almost right: #E01010 looks red, but it is not #FF0000, so it lands on a layer of its own with its own settings.

In both kinds, a filled shape is an area, and areas are engraved. Three things put a fill where a cut should be:

• Fill, no stroke. Common in files made for printing or for a vinyl cutter, and in text converted to paths.
• It is a picture, not a vector. A PNG or JPG, or an SVG that only wraps a picture, has no lines to follow. xTool's help pages say a bitmap can only be engraved; the same is true in the other programs.
• Live text. A font the laser software doesn't have may be swapped or dropped. Convert text to paths first.

Where the thick lines come from

Design programs give every new shape a default outline, often 1 pt (0.35 mm) or 1 px. At 96 px per inch, 1 px is 0.26 mm, ten times a 0.025 mm hairline. Files made for print, vinyl or sublimation use visible line weights on purpose. Scaling a design up can scale its outlines too. And black, the default colour, is the colour many shared laser files use for engraving.

When the cut runs but the piece won't drop out: open paths

An open path is an outline whose start and end don't meet. On screen the gap can be a fraction of a millimetre. The laser cuts exactly what is there, so the gap stays as a little strip of uncut material and the piece hangs on by it. Open paths also can't be filled: LightBurn's documentation says it cannot work out an area to fill on an open shape and warns when one sits on a Fill layer.

How to check your file

• Switch to an outline view: Inkscape View > Display Mode > Outline, Illustrator View > Outline (Ctrl/Cmd+Y). A shape that disappears in outline view, or looks different, was relying on a fill.
• Select a line that should cut and read its fill and stroke: you want a stroke and no fill. Read the stroke width with the units set to mm, so you are not comparing points with pixels.
• Read its colour as a hex code, not by eye.
• Check that the stroke opacity is 100%. The same library guide lists opacity as the next thing to check when a thinner line alone doesn't fix it.
• Look for open paths. In LightBurn, Edit > Select Open Shapes selects every open shape at once, and open shapes show their start and end nodes in green when you edit nodes. In Inkscape and Illustrator, zoom in on corners and joins: two end nodes side by side mean the path is open there.
• Before you press start, look at the layer or job list in your laser software: every cut line should sit in a cut layer.

How to fix it by hand

Turn a fill into a cut line

• Inkscape: select the shapes, open Object > Fill and Stroke (Ctrl+Shift+F), set Fill to none and Stroke paint to a flat colour. Text first: Path > Object to Path.
• Illustrator: set fill to none and give the shape a stroke. Text first: Type > Create Outlines.
• LightBurn: what happens is set by the layer, not the shape. Put the shapes on a layer in Line mode to cut or score along them; Fill mode engraves the inside.
• Glowforge and xTool: once the shape has a stroke and no fill, the app lists it as something you can set to Cut. A picture stays engrave-only: trace it into vectors first (see convert an image to SVG for laser cutting).

Make the lines thin, in an exact cut colour

1. Select every cut line. Set the fill to none and the stroke to your design program's hairline, or 0.025 mm (0.001 in) if it has none.
2. Give cut lines one exact colour and score lines another. Red #FF0000 for cut and blue #0000FF for score is a common convention; use what your laser software expects, and type the hex code instead of picking by eye.
3. If your program scales outlines with the shape, turn that off before you resize anything.
4. Save the SVG with its size in mm and open it in your laser software once more to check the layers.

Close an open path

• Inkscape: with the Node tool (N), select the two end nodes. If they sit on top of each other, click Join selected nodes (Shift+J). If there is a gap, use Join selected endnodes with a new segment. If the two ends belong to two separate paths, select both and Path > Combine (Ctrl+K) first.
• Illustrator: with the Direct Selection tool, select the two end points and choose Object > Path > Join (Ctrl/Cmd+J).
• LightBurn: Edit > Close Path closes a shape whose ends are very close (the docs say up to 0.5 mm). For bigger gaps use Edit > Close selected paths with tolerance, and for a shape broken into many segments, Edit > Auto-Join Selected Shapes (Alt+J).

Selling the file? Say in the description which colour cuts and which scores, and that the lines are hairlines. A buyer whose software works the other way can remap it in a minute.

Or check and fix it free in your browser

Drop the SVG into the SVG Checker & Fixer. It runs on your device and nothing is uploaded. It flags any cut or score line wider than 0.1 mm or with a fill ("Your file only engraves instead of cutting"), and lists every line colour in the file with a guess for each one: cut, score, engrave or leave as is. Change any guess you know better and fix: you get an SVG in mm with the cut and score lines as 0.01 mm hairlines in exact red and blue, checked again.

On the tag above, the checker found no line in a cut colour, so its cut checks could not run yet. The fixer guessed black as the cut and left grey for us to choose; set to Score, the fixed file passed every rule. The same tag drawn in red and blue, but with 0.35 mm and 0.5 mm lines, failed one rule with "max stroke-width=0.500 mm (limit 0.1)", and passed after the fix. Checking is free for as many files as you like, with no sign-up; the one-press fix is free for 3 files a day.

Check my SVG free

Try it with the sample file

Save this as tag.svg and drop it into the checker:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Sample: a gift tag drawn with a drawing program's default outline (about 1 pt = 0.35 mm, black)
     and a grey 0.5 mm line meant to be scored. Many laser programs treat lines this thick as engraving. -->
<svg xmlns="http://www.w3.org/2000/svg" width="80mm" height="50mm" viewBox="0 0 80 50">
  <path fill="none" stroke="#000000" stroke-width="0.35" d="M20,5 L70,5 A5,5 0 0 1 75,10 L75,40 A5,5 0 0 1 70,45 L20,45 L5,25 Z"/>
  <circle cx="16" cy="25" r="3" fill="none" stroke="#000000" stroke-width="0.35"/>
  <path fill="none" stroke="#808080" stroke-width="0.5" d="M28,12 L68,12 L68,38 L28,38 Z"/>
</svg>

What the fixer gave back, with grey set to Score:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Fixed in the browser with the free Laser SVG Checker & Fixer by Moc: https://moc.thejunix.com/en/laser-svg-checker -->
<svg xmlns="http://www.w3.org/2000/svg" width="80mm" height="50mm" viewBox="0 0 80 50">
<g id="score">
<path fill="none" stroke="#0000FF" stroke-width="0.01" d="M28,12L68,12L68,38L28,38L28,12Z"/>
</g>
<g id="cut">
<path fill="none" stroke="#FF0000" stroke-width="0.01" d="M20,5L70,5C72.7614,5 75,7.2386 75,10L75,40C75,42.7614 72.7614,45 70,45L20,45L5,25L20,5Z"/>
<path fill="none" stroke="#FF0000" stroke-width="0.01" d="M13,25C13,26.6569 14.3431,28 16,28C17.6569,28 19,26.6569 19,25C19,23.3431 17.6569,22 16,22C14.3431,22 13,23.3431 13,25Z"/>
</g>
</svg>

Questions

Why does my laser engrave instead of cut?

The shape has a fill, the line is wider than your laser software's limit for a cut, it is in a colour set to engrave, or the file is a picture. Make each cut line a thin stroke with no fill, in your cut colour, and trace pictures into vectors.

What stroke width should cut lines be for laser cutting?

A hairline: your design program's hairline setting, or about 0.025 mm (0.001 in). Software that sorts by colour ignores the width, so a hairline in the right colour works in both kinds.

What is an open path in a laser file?

An outline whose two ends don't meet, even by a hair. The laser cuts the line but leaves the gap uncut, so the piece stays attached, and the shape can't be filled for engraving.

How do I find open paths in my SVG?

In LightBurn use Edit > Select Open Shapes. In Inkscape or Illustrator, zoom in on corners with the node tool and look for two end nodes side by side, or drop the file into a free checker that lists each gap with its position.

Does a thicker line make a wider cut?

No. The beam follows the centre of the path. The width of the cut comes from the beam and the material (the kerf), not from the line in the file.

More fixes for laser files

• Laser cuts the same line twice
• SVG imports at the wrong size
• Bridges too thin: parts fall out or snap
• Convert an image to SVG for laser cutting
• Laser cutting double lines from a traced image
• Laser Studio: describe a design or drop a picture, get checked SVG, DXF and PDF files in mm