Why are duplicate lines and open paths a problem in laser files?

Question

Accepted Answer

Duplicate lines can make the machine cut the same path more than once.

Duplicate lines can make the machine cut the same path more than once. Artwork built by stacking shapes or masking parts of shapes is one way they appear. In LightBurn, open shapes can’t be filled or given a kerf offset, because those functions need closed shapes, and a gap too small to see can leave a shape open. There, open paths belong on a Line Mode layer, which follows them as lines, often to score, instead of filling them. Cleanup turns stacked duplicate lines and an open gap into single lines and closed shapes A before and after comparison. On the left, two adjacent rectangles share an edge that is drawn twice as two stacked lines labeled duplicate edge, and the top edge of the right rectangle has a dashed circle around a gap labeled open gap. The segment count is labeled more than expected. An arrow points right to the after view: the same two rectangles, now with one shared line labeled one line, cut once, and both outlines closed. The segment count is labeled as expected. Below, a note says to re-export and then check the machine preview. Before cleanup stacked lines, open gap After cleanup each line once, shape closed open gap duplicate edge segments: more than expected one line, cut once closed shape segments: as expected Re-export, then check the machine preview. The offset between the two duplicate lines and the size of the gap are exaggerated so you can see them. Cutting a shared edge once can be a deliberate, locally accepted strategy; the problem is an accidental overlap. Conversion can change geometry, so check the preview after you export again. Inspect in wireframe mode, use duplicate-selection or path-cleanup tools, and compare expected versus actual segment counts. Shared-edge cutting should be an intentional, locally accepted strategy—not an accidental overlap. After cleanup, re-export and check the machine preview, since a file can import differently from how it looked in the design program.

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