Open contours: fill does not work on my DXF
You set a layer to Fill and nothing happens, or only part of the design is engraved, or LightBurn warns that some shapes are open. The shapes look closed on screen, yet the software disagrees.
Short answer: a shape can only be filled if its outline is one closed loop. DXF exports often split outlines into separate segments or leave a tiny gap at the end. Find the open shapes, join them, and remove duplicate lines.
Three causes
1. The outline is split into pieces
Some exporters write every segment of a curve as its own line. On screen it is a circle; in the file it is dozens of unconnected arcs. In our tests, one common export path produced hundreds of separate segments and no closed shape at all after converting a simple design to paths.
2. The ends almost meet
The last point stops a few hundredths of a millimetre away from the first. Invisible, but the shape is open.
3. Lines that are really strokes
A line drawn with a thick stroke looks like a filled bar in your design software. In a DXF only the centre line remains, which is open by nature. If you want the bar, convert the stroke to a shape first (Inkscape: Path → Stroke to Path; Illustrator: Object → Path → Outline Stroke).
Find the open shapes
- LightBurn: Edit → Select Open Shapes. Whatever gets selected is open. LightBurn also warns when you set an open shape to Fill and can show you which ones.
- xTool Studio: in our tests it closed open paths on its own when we chose Engrave, without warning, sometimes joining the wrong points into triangles. Check the engrave preview closely.
- Inkscape: with the node tool, an open path shows its two end nodes.
Close them
- LightBurn: select the shapes and use the close and auto-join commands in the Edit menu (they join ends that are within a tolerance you set).
- Inkscape: node tool, select the two end nodes, Join selected end nodes (Shift+J). To merge separate pieces first, select them and use Path → Combine.
- Illustrator: select the two end points with the Direct Selection tool, then Object → Path → Join (Ctrl+J).
Do not forget duplicate lines
A filled shape with an outline, or a copy pasted in place, gives two identical lines on top of each other. The laser cuts them twice: more burn, a wider kerf, sometimes a fire risk on thin material. In LightBurn, Edit → Delete Duplicates removes them; note how many objects disappear.
Or convert with clean contours from the start
Our converter keeps each shape as one polyline instead of loose segments, closes contours whose ends are within 0.1 mm, closes filled shapes the way the SVG draws them, removes duplicate lines, and tells you how many open paths are left so nothing is a surprise. Hinge lines and score lines stay open, as they should. Invisible shapes (no fill and no outline, like the artboard rectangle Illustrator adds) are left out, so the laser never cuts around your whole page.
Convert an SVG to DXFShould every line be closed?
No. Score lines, single cut lines and living hinges (the rows of short cuts that make plywood bend) are open on purpose. Only shapes you want to fill or engrave as an area need to be closed. When you check a file, compare the number of open shapes with what the design should have.
Questions
What is an open contour?
A shape whose start and end points are not joined. The laser can follow it as a line, but software cannot fill it because it has no inside.
How do I find open shapes in LightBurn?
Use Edit, Select Open Shapes. Everything selected is open. LightBurn also warns when you set an open shape to Fill.
Should every line be closed?
No. Score lines, living hinges and single cut lines are meant to be open. Only shapes you want to fill or engrave as areas must be closed.