Laser Cutter File Prep

Going from CAD to cuts takes some extra legwork in the middle.

Offsetting files

For cutting through a material, most laser cutters require a vector graphic. Unlike raster images, which store pixels, these filetypes contain information that store paths. Paths are usually represented as a series of lines or arcs, although they may also contain fancier mathematical representations such as polylines and Bezier curves. When a laser cutter gets to work on this file, it is literally tracing these paths with the beam, which has the effect of cutting through the material.

Laser cutter beams aren't simply thin lines. These beams are conical, and they have a finite thickness. These properties are driven by the type of lens that's mounted on the head of the machine's xy stage.

When the beam cuts through a part with this tapered beam, it effectively creates a taper on the edge of the part too. This taper is called the kerf. On some materials like wood, this taper is often unnoticeable, but on plastics like Acrylic and Acetal Homopolymer (Delrin), it can be seen with the naked eye.

Both the kerf and the nonzero thickness of the beam can cause issues when trying to fit interlocking laser-cut pieces together. Luckily, a simple constant offset factor applied to all edges of a part file can correct this issue in most use-cases. Unfortunately, most laser cutters do not apply this constant offset factor; rather, they simply literally trace the paths defined in the file. Howerver, there are multiple places where we can apply this offset.

In the native CAD File

Fancier programs like Solidworks will let us offset faces of the part directly. In Solidworks, this feature is called Move Face from the Direct Editing menu.

From the Exported CAD File

Once the part converted to a vector graphic, it can be manipulated with vector graphic tools. Solidworks can work with DXFs if it reimports them as sketches. Adobe Illustrator can also apply offsets.

From the CAM Program

Some laser cutters (usually DIY ones) require an extra step of post-processing to go from vector-graphic format to a format that the machine can read. (These machines are admittedly rare and usually hobbyist projects.) This file format is usually GCode. Cam programs that convert from vector graphic formats (like DXF) to machine-readable formats often have an offset setting. This appearance is usually because machine-readable formats like GCode are intended for machines with cutting tools that have a non-negligible thickness, like endmills on a milling machine.

Examples

See the dxf2gcode project.

On the laser cutter itself

I don't know of any laser cutters that directly perform offset compensation on a file. If you do, drop me a note!

Various Laser Cutter Workflows

Various brands require various input files. Here's a quick breakdown.

Universal Laser

Universal laser cutters require PDFs with red hairline thickness lines.

1. Create an offset DXF from one of the methods above.
2. Import the DXF into Inkscape.
3. Select all lines. From Object → Fill and Stroke, set stroke width to 0.001-in.
4. Save the file in PDF format.
5. Open the PDF from the Universal Laser Cutter interface, select your material settings, and get cutting!

Epilog Laser

1. Create an offset DXF from one of the methods above.
2. TODO: finish these instructions.