Updated July 6, 2026

Why does my laser cut the same line twice?

You send a DXF/DWG file to your laser cutter and the head traces the same path twice. The edges come out burnt, the job takes far longer than it should, and on thin materials the second pass can ruin the part. Yet nothing looks wrong in your drawing — every line appears exactly once on screen.

The symptoms

Typical signs that your file contains duplicated geometry:

• The laser visibly passes twice (or more) over some contours, or all of them.
• Cutting time is roughly double the estimate for the drawing's length.
• Edges are burnt, melted, or wider than on other jobs with the same settings.
• In LightBurn, shapes that should be filled render as a plain outline, or vanish from the Preview window — two identical stacked paths visually cancel each other out in Fill mode.
• Your laser software (LightBurn, LaserGRBL, RDWorks…) reports a total cut length far greater than expected.

The cause: duplicate lines in the DXF/DWG file

A DXF or DWG file can contain two identical segments stacked exactly on top of each other. On screen they render as a single line — you cannot see the difference, even at maximum zoom. But every entity in the file gets cut: a doubled line is cut twice.

These duplicates are almost never drawn by hand. They are artifacts of how the file was produced:

• Exports from vector software (Illustrator, Inkscape, CorelDRAW): shapes that carry both a fill and a stroke, or paths overlapping across layers, can export each edge twice.
• 3D-to-2D projections (Rhino's Make2D, Fusion 360 sketches projected from bodies, SolidWorks flattened views): an edge shared by two faces is often projected once per face, producing two identical curves in the same place.
• Paste-in-place and overlapping blocks in CAD: pasting geometry at its original position, or inserting a block on top of already-drawn entities, silently stacks one copy on the other.
• Image tracing (scan or raster PDF → DXF): the tracer follows both edges of a thick stroke and produces two nearly parallel contours, a fraction of a millimeter apart. They are not exact duplicates, but the laser does cut twice.

Shouldn't the laser software fix this by itself?

Partially, sometimes. LightBurn — the most widespread control software among laser cutters — offers two relevant features:

• Edit → Delete Duplicates (Alt+D) removes duplicated objects — but only if they are ungrouped and strictly identical in size, shape and position. Two curves that differ by a hundredth of a millimeter, a duplicate hidden inside a group, or a long segment covered by several short ones slip through.
• "Remove overlapping lines" in the optimization settings tries to eliminate redundant passes at cut time. In practice, the option regularly fails on partial overlaps and near-duplicates — the LightBurn forums are full of geographic maps with regions, or nested parts sharing edges, that it does not fix.

And in both cases, the file itself stays dirty: the problem comes back as soon as you reopen it elsewhere or share it.

What about CAD tools?

• AutoCAD's OVERKILL is the most complete tool: it handles exact duplicates and can merge collinear segments that partially overlap. But it requires an AutoCAD license — which most laser users don't have — and understanding its tolerance options so it removes neither too much nor too little.
• Rhino's SelDup only selects perfect duplicates: two curves that differ by a micron escape it, and so do partial overlaps.
• Illustrator and Inkscape have no reliable built-in way to find stacked paths; you end up walking the layer tree object by object.

Whatever the tool, you have to start over on every export, because the duplicates come back as soon as the file is regenerated.

Clean the file in one click with Razoar

Razoar automatically removes duplicate and overlapping segments from your files:

1. Drop your file in the app — no signup required for the preview.
2. The live preview shows exactly which segments will be removed, overlaid on your drawing, before you commit to anything.
3. Adjust the tolerance if your file contains near-duplicates — typically from image tracing — rather than exact copies.
4. Export the cleaned file and send it to your laser.

Unlike a deduplication done in the laser software, the file itself gets fixed: the problem does not come back. Razoar also handles the neighboring defects that inflate cutting time — micro-segments, partially overlapping lines, and collinear chains that should form a single segment.

Your file never leaves your browser — the cleaning runs locally via WebAssembly, so your confidential drawings stay on your machine.

Try it on your file →