Why is my laser cutting the same line twice?
Updated Nov 11, 2026
Short answer: The file has doubled lines: a shape pasted twice, a line drawn twice, or two shapes that share an edge. Remove the extra copies.
Check your file now (free)
What do you cut with?
Drop your SVG or DXF file here
or
Free. Nothing is uploaded: the check runs on your own computer.
Marks: open ends cut twice dots and tiny bits text and pictures
Size
Download
More settings
Changing these checks the file again.
Why it happens
Your laser cuts every line in the file. If a line is in the file twice, it gets cut twice, even with passes set to 1. The second pass burns the edge darker, wastes time and can snap thin parts.
There are three usual causes:
- A shape pasted twice. Copy and paste, or "duplicate", leaves a second shape exactly on top of the first. On screen it looks like one.
- A line drawn twice. Common in DXF files from CAD programs and in files from online converters.
- Two shapes that touch. When parts are packed edge to edge to save material, both outlines run along the shared edge, so that edge is cut twice.
How to fix it
- Drop your file into the checker above. Doubled lines and shared edges are marked in orange.
- Press "Fix everything I can". Extra copies are removed. Where two shapes share an edge, the edge is kept on one shape only.
- Download the SVG and open it in your laser software as usual. Run a preview: each line should now be traced once.
By hand in LightBurn, select everything and use Edit › Delete Duplicates, and turn on "Remove overlapping lines" in Optimization Settings. In Inkscape or Illustrator, select a shape and move it aside to find a copy underneath, then delete the copy.
Real example: before and after
What the checker found
- Doubled lines: 1 shape is drawn twice
- 1 shared edge between touching shapes
- Size: 100 mm (3.94 in) wide × 40.0 mm (1.57 in) tall
What was fixed
- Removed 1 shape that was drawn twice.
- Removed 1 shared edge so each edge is cut once.
Download: before (SVG) · after (SVG)
Questions
I set 1 pass. Why does the laser still go over a line twice?
Because the line is in the file twice. Passes repeat every line; a doubled line gets cut once per copy on every pass. Remove the copy and the line is cut once.
Does LightBurn remove doubled lines by itself?
LightBurn has "Remove overlapping lines" in Optimization Settings, which skips lines that overlap when it plans the cut, and Edit › Delete Duplicates, which removes identical shapes. Some users report overlaps it misses, for example when the lines were imported as one long path. Cleaning the file itself avoids that.
Two parts touch on purpose to save material. How do I cut the shared edge once?
Remove the shared edge from one of the two parts, so only one outline runs along it. The checker does this for lasers when you press Fix. For plasma and metal shops it reports it instead, because those need a gap between parts.
How can I see doubled lines in my design program?
You usually cannot: two copies of a line look exactly like one. In Inkscape or Illustrator, drag the shape aside to see if another one is under it. The checker marks them in orange.