Preparing laser files: vectors, text, kerf and photos
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Many laser problems do not arise at the machine but in the file. Duplicate lines, open paths or a photo that is too dark lead to burnt edges, parts that do not fall out, or muddy engravings. Here you learn how to prepare files so that the laser does exactly what you want.
Vector or pixel
A vector file describes lines and shapes mathematically. It can be enlarged as much as you like without becoming blurry. The laser can follow vectors as a line (cutting, scoring) or fill them as an area (engraving).
A pixel file (raster graphic) consists of individual image points. Photos are always pixels. The laser can only engrave pixel images line by line, but cannot cut them. If you have a logo as a PNG and want to cut it out, you first have to convert it to vectors, for example with the trace function in Inkscape or LightBurn (“Trace Image”).
File formats
| Format | Type | Notes |
|---|---|---|
| SVG | Vector | standard format for laser work, open, readable by almost any software |
| DXF | Vector | from CAD programs, good for technical parts; check the unit of measurement on import |
| AI | Vector | Adobe Illustrator; older versions import better than new ones |
| Vector and pixel | can contain both; check what arrived after importing | |
| PNG | Pixel | lossless, supports transparency, good for graphics |
| JPG | Pixel | compressed, usual for photos; compression artefacts get engraved too |
Check the size after every import. SVG files from different programs sometimes calculate with different resolutions, and the part then arrives too large or too small.
Lines for cutting
For a clean cut, the lines have to follow a few rules:
- Hairlines: The stroke width does not matter to the laser, it always follows the centre of the path. A thin line does show you more precisely on screen where it will cut, though. What matters is that cut lines have only an outline and no fill, otherwise the software may engrave the area as well.
- Closed paths: Parts that are supposed to fall out need a closed outline. In LightBurn you find open paths under “Edit” with “Select open shapes”. Join gaps with “Close Path” or, in Inkscape, with the node tool.
- Remove duplicate lines: If two lines lie on top of each other, the laser cuts twice. That gives wider, more heavily burnt edges. In LightBurn you find the function “Delete Duplicates” under “Edit”. Duplicate lines often arise when parts butt directly against each other or a file comes from a CAD program.
Converting text to paths
If you pass on a file containing text or open it on another computer, the font may be missing there. The software then replaces it with another one. So convert text to paths before exporting. In Inkscape this is done via “Path” and “Object to Path”, in LightBurn with “Convert to Path”. After that, the text can no longer be edited as text, so keep a copy with editable text.
Bridges in stencil lettering
When you cut out letters, the inner parts of A, O, B or R fall out. For stencils you therefore need bridges, small webs that connect the inner part to the rest. You can use a stencil font that already has these webs, or add bridges yourself. LightBurn has a Path Bridges function for this, with which you place webs at even intervals in the outlines. With wood, do not make the webs narrower than about 1 mm, otherwise they break or burn away completely.
Kerf compensation for slot-together joints
When cutting, the laser removes a narrow track of material, the kerf. Depending on the machine, focus and material, it is often in the range of a few tenths of a millimetre. For decoration it hardly matters. For slot-together joints and boxes with finger joints, however, the parts become smaller by this kerf, and the joint fits loosely.
Here is how to compensate:
- Cut a square with an edge length of exactly 20 mm from your material.
- Measure the cut-out part with callipers. If it is 19.8 mm, the kerf is 0.2 mm.
- In LightBurn, enter a starting value of about half of that under “Kerf Offset” in the cut layer, here 0.1 mm. Positive values move the path outwards. The function only works on closed shapes.
- Test with a small slot-together joint and adjust the value.
Many box generators online have their own field for the cut width. In that case you compensate there and not additionally in LightBurn.
Order: inside before outside
If you cut the outer contour first, the part can shift or tilt slightly downwards. The inner cuts then end up beside it. So the rule is: engrave first, then cut the inside, and the outside last. In LightBurn you set this in the optimisation settings with “Cut inner shapes first”. It also helps to put engraving and cuts on different layers and arrange the layers in the right order. More on layers is in the article LightBurn.
Preparing photos for engraving
A photo that looks good on screen often ends up too dark on wood. Wood has its own base tone, and burnt dots run into each other slightly.
- Greyscale: Convert the image to greyscale. The laser has no colours anyway.
- Contrast and brightness: Raise the contrast and lighten the midtones. Deep shadows should not be completely black, otherwise details disappear.
- Sharpening: Light sharpening helps, and edges stay more distinct after engraving.
- Background: A calm or removed background draws the eye to the subject and saves time.
Dithering modes: Most lasers only know on or off. Dithering translates grey tones into a pattern of dots. LightBurn has these modes, among others:
| Mode | Suitable for |
|---|---|
| Threshold | pure black-and-white graphics |
| Jarvis, Stucki | photos with soft transitions |
| Dither | photos, general choice |
| Atkinson | images with areas and gentle gradients, can lose very light and dark regions |
| Ordered, Halftone, Newsprint | even dot patterns, Halftone and Newsprint rather at high resolution |
| Grayscale | controls the power per pixel, more for CO₂ lasers and specially prepared images |
DPI and line interval: The resolution of the engraving results from the line interval: DPI = 25.4 divided by the line interval in mm. An interval of 0.1 mm corresponds to 254 DPI. For photos on wood with a diode laser, 0.08 to 0.1 mm is a usual start. If the interval is smaller than the laser spot, the lines overlap and the image becomes dark. More on this in Laser parameters. Always engrave photos first as a small section on an offcut, see Material test.
Free tools
- Inkscape: free, open-source vector program for Windows, macOS and Linux. It can draw, trace, convert text to paths and export as SVG or DXF.
- GIMP: free image editing for greyscale, contrast and cutting out subjects.
- Box generators in the browser produce slot-together boxes with finger joints as SVG.
Finally, check every file in the preview of your laser software. There you can see which paths will be processed how before the laser starts.
Continue with: LightBurn, Laser parameters and Laser engraving wood.
How to prepare photos for the laser and which image mode suits is explained in Laser engraving photos.