How to prepare a file for laser cutting (DXF, SVG, kerf, bridges)
Most quote delays aren't about price. They're the shop writing back to ask what units the file is in, which lines are cuts, and why there are two copies of every path. Fix those before you post and you'll get bids faster and lower, because the shop isn't pricing in an hour of cleanup.
Formats, in order of preference
- DXF — the industry default. Every laser controller reads it, and every vector or CAD program exports it. Pick R12/R14 or 2000 if offered; newer versions carry features some controllers ignore.
- SVG — fine for CO2 shops, common for Glowforge and hobby-tier machines. Watch the scale (below).
- AI / EPS / vector PDF — accepted by most, but flatten gradients and masks and convert text to outlines first.
- PNG / JPG — not a cut file. Shops can auto-trace, but the result is lumpy and they'll charge $30–90 (USD) to redraw it. Only send a raster if it's for engraving a photo.
For sheet metal, send DXF.
Scale and units
The number one problem. SVG has no fixed unit: depending on the exporter, a 100 mm part opens at 75 mm in another program.
Draw at 1:1. State the units in the file name and the brief. bracket_v3_mm.dxf. Then add a 10 mm × 10 mm reference square on a separate layer, labeled, so the shop can check the import with one glance. Delete it from the cut layer.
Layers: cut, score, engrave
A laser does three different things and needs to know which is which:
- Cut — through the material. Vector line.
- Score / vector engrave — a fine line partway in. Vector line, lower power.
- Raster engrave — filled area, burned in a back-and-forth pass like a printer. Filled shape.
Put each on its own layer, and name the layers. If your program doesn't do layers, use colors: the common convention is red = cut, blue = score, black = raster. Say which convention you used. A shop that gets one layer of black lines has to guess.
Closed paths, no duplicates, no overlaps
Every cut outline must be a closed path. A gap of 0.1 mm at a corner means the part doesn't fall out of the sheet. Illustrator: Object → Path → Join; Inkscape: Path → Combine; CAD: the "open contour" check.
Duplicate lines are the second most common problem. Two paths on top of each other means the laser cuts twice: double the time, and on acrylic a melted, charred edge. Autotrace, copy-paste and DXF export from 3D software all produce them. Inkscape's Remove Duplicate Lines extension catches them.
Overlapping shapes should be unioned into one outline. Two overlapping circles as separate paths cut a figure-eight with a slice through the middle.
Text must be converted to outlines (Create Outlines / Object to Path). Otherwise the shop's machine substitutes a font and your sign ends up in Arial.
Kerf
The laser removes material. The width of that removed line is the kerf: about 0.1–0.3 mm on CO2 depending on material and thickness, 0.1–0.2 mm on fiber. Cut a 50 mm square and you get a 49.8 mm square; cut a 10 mm hole and you get a 10.2 mm hole.
For most parts it doesn't matter. For anything that has to fit — slots, tabs, finger joints, press-fit pins, box lids — it does. Two options:
- Tell the shop to offset for kerf. Most controllers do it automatically. Say "parts must fit as drawn; please apply kerf compensation."
- Offset it yourself. Draw slots kerf-narrower and tabs kerf-wider. Only do this if you know the shop's kerf, which you don't until they tell you.
The first option is right nearly always. If the fit really matters, ask for a first-article test piece and approve it before the batch runs.
Minimum feature size
Thin walls and tiny holes fail. Rules of thumb:
- Minimum wall between two cuts: at least the material thickness, ideally 1.5×.
- Minimum hole diameter: about the material thickness on CO2, 1× on fiber (smaller is possible but the edge gets rough).
- Minimum letter height for cut-through text: about 6 mm for the counters (the holes in "a", "e", "o") to survive.
- Engraved text: 2 mm and up is legible on most materials.
Bridges and stencils
If you cut a letter "O" through a sheet, the middle falls out. For stencils and any design where inner pieces need to stay attached, add bridges (tabs): small uncut gaps, 1–2 mm wide, that hold the island to the surrounding material. Use a stencil font, or draw the bridges by hand and knock them out of the cut path.
Some shops also leave micro-tabs on small parts so they don't drop through the bed. If you want parts fully free, say so.
Bed size
You don't have to nest; the shop will, tighter than you. But know the common beds: hobby CO2 300×500 mm, shop CO2 600×900 or 900×1300 mm, fiber 1500×3000 mm. A part bigger than the bed must be split, and that's your design decision, not the shop's.
The pre-flight checklist
Before you upload:
- [ ] Vector format (DXF preferred), text outlined
- [ ] 1:1 scale, units named in the file name, reference square included
- [ ] Cut / score / engrave on separate named layers or colors, convention stated
- [ ] All cut paths closed
- [ ] No duplicate or overlapping lines
- [ ] Features respect minimum wall and hole size for the thickness
- [ ] Bridges added where islands must stay attached
- [ ] Largest part fits a standard bed, or the split is designed
- [ ] Material and thickness written in the brief, not just implied by the drawing
Do that and the shop's first reply is a price, not a question. What that price should look like is on the price guide, and when the file is ready, post it once and let several shops bid on it.