Preparing a DXF for laser cutting

DXF is the format nearly every cutting machine can read. But “a DXF” is not enough: for the cut to work first time, the file has to follow a few rules. These are the ones that actually matter.

What has to be inside

• Closed outlines. Every part must be a line that returns to where it started. An outline left open by a tenth of a millimetre is invisible to the eye, but the machine treats it as a mark, not a cut.
• No double lines. Two overlapping segments get cut twice: the edge burns, the part comes out smaller, and on some materials it catches fire.
• Declared units. A file without units is guessed at by the machine software, and a 150 mm part can become 150 inches.
• Scale 1:1. No resizing on the way out, ever.

Exporting from Plyjoin, all four are guaranteed: the outlines are closed because they are computed from the solids rather than drawn by hand, and the unit is written inside the file.

The layers

The DXF comes out with two layers, and it is worth knowing before you open it on the machine:

• CUT — the outlines to cut. This is the only one that should be set to “cut”.
• LABELS — the part names. They are for you, so that you are not left with twelve identical rectangles on the bench and no idea which is which. In your machine software you can switch it off, or set it to low-power engraving: the names stay written on the wood.

If you do not want them at all, the “Part names in the DXF” checkbox removes them.

Millimetres or inches

The switch at the top right of the app decides the units for everything: sizes on screen, preview and export. Choose before exporting, not after.

SVG, when it helps

SVG comes out of the same panel and is useful in two cases: when you use Inkscape or Illustrator as an intermediate step, and when you send the file to an online cutting service, which often prefers it. It carries the same geometry as the DXF.

The three checks before you press “cut”

1. Look at the preview. The cutting layout shows exactly what will be cut. If a joint is not visible there, it will not be on the wood either. 2. Check the overall size. The total is shown at the top of the preview: it has to fit your bed. 3. Cut a test piece. One joint, ten minutes. It is the only way to know whether thickness, clearance and kerf are right for that material.

Try it now

Open the app, press “Export DXF…” and look at the preview: that is the file you would hand to the machine, with nothing in between.