Laser Cutting Files: DXF Specifications and Kerf
A practical laser cutting file guide: DXF units, path topology, kerf measurement and compensation, minimum features, and clean cut/engrave layers.
Laser cutting and engraving are subtractive processes, and they are unforgiving about units, cut width, and path topology. A file that looks correct on screen can still produce parts that do not fit or cuts that wander off the intended line. The issues are not mysterious; they come from a small set of conventions that every well-prepared DXF respects. This guide covers the specifications that matter and the corrections that make parts come out right.
Why DXF is the default for laser work
DXF is a plain-text CAD interchange format. It stores lines, arcs, polylines, splines, and layers, which map almost directly onto what a laser controller needs: move here, cut to there, raise the head. It has no notion of stroke width or fill colour, so there is no ambiguity about what gets cut. Many laser services accept SVG too, but DXF is the more conservative choice when the receiving software is unknown.
Specify units explicitly
The most common DXF failure is a unit mismatch. A DXF file can declare millimetres, centimetres, inches, or nothing at all. If your file is drawn in millimetres and the machine assumes inches, a 100 mm part becomes a 100 inch part — twenty-five times too large. Always export with an explicit unit declaration and confirm with the service or in the controller software. When in doubt, state the units in the filename or job notes as well.
A simple sanity check: include a known reference dimension in the drawing, such as a 10 mm square in a corner or a note with a measured length. If the reference measures correctly after import, the rest of the file probably will too.
Kerf: the gap the laser removes
Every cut removes material. The width of that removed strip is the kerf, typically 0.1 to 0.4 mm depending on the laser, lens, material, and power. This matters whenever two parts must fit together: a tab intended to fit a slot exactly will be too tight, because the slot is narrower by one kerf and the tab is wider by nothing.
Kerf compensation means offsetting the cut path outward or inward by half the kerf so the final part matches the intended dimension. For outside contours you cut slightly outside the line; for holes, slightly inside. Many laser controllers can apply this automatically if you enter the measured kerf; alternatively, compensate in your design software.
Measure the kerf for your material and machine rather than assuming a value. Cut a test square, measure it with callipers, and compare to the file dimension. Run the test again after changing material, power, or focus.
Path topology that the machine can follow
- Closed contours. Every shape to be cut must be a closed loop. Open paths may be ignored or interpreted as engraving lines.
- No self-intersections. A path that crosses itself confuses the cut order and can leave uncut slivers.
- Join coincident nodes. Nearly-touching endpoints create double cuts and fragile webs of material.
- Separate cut and engrave layers. Put cuts, scores, and raster engraves on distinct layers named clearly so the operator can assign power and speed per layer.
- Remove duplicate geometry. Overlapping identical paths cause the laser to cut the same line twice, widening the kerf.
Minimum feature size and spacing
A laser cannot cut details smaller than its spot size, and thin material breaks when the remaining web is too narrow. As a rule of thumb, keep details above 0.5 mm for rigid materials and above 1 mm for thin or brittle ones, and keep the spacing between adjacent cuts at least a kerf and a comfortable margin so the material stays strong. Text below about 5 mm height is better engraved than cut.
Avoid designs where two cut lines run parallel closer than the kerf. The material between them vaporises and the part becomes a single slit rather than two edges. If a detail needs to look thin, engrave it instead of cutting it out.
Engraving versus vector cutting
Vector lines cut; raster fills engrave. In most workflows, the distinction is carried by layer type or colour: a black line layer cuts, a filled shape layer engraves. Decide before export which is which, and keep a separate engraving layer for anything that must not go all the way through, such as text on a panel face.
Engraving resolution is a function of the laser's step-over, not the vector node count. Still, keeping the engraving artwork clean matters: gradients cannot be engraved as gradients, and a photo engrave needs a dithered or halftoned raster with deliberate contrast.
| Symptom | Likely cause | Fix |
|---|---|---|
| Parts fit too tight or too loose | Kerf not compensated | Measure kerf, offset contours by half its width |
| Part comes out the wrong size | Unit mismatch in the DXF | Declare units and add a reference dimension |
| Some outlines not cut | Open paths or duplicate geometry | Close contours, remove duplicates |
| Engraving cuts through | Engrave layer assigned as cut | Separate and label cut versus engrave layers |
| Thin details crumble | Feature smaller than spot or too little web | Enlarge detail or engrave instead of cutting |
A practical DXF export checklist
- Draw at final size in consistent units and set those units in the file.
- Close every cut contour and remove self-intersections and duplicate paths.
- Put cut, score, and engrave geometry on separate, clearly named layers.
- Measure your machine's kerf for the material and compensate if the design needs an exact fit.
- Check minimum feature size and spacing against the material.
- Include a reference dimension and note the units in the job notes.
- Import the file into the controller once and preview before starting the job.
Laser work rewards files that are simple, explicit, and unambiguous. The geometry should be closed, the units should be stated, and the kerf should be measured rather than assumed. Once those are right, the design translates directly into parts that fit.
Put this into practice
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