DXF vs DWG vs STEP vs STL

The difference between a mesh and a solid decides whether a shop can quote your part. It decides whether you can edit the part, whether a shop can quote it, and whether the file is CAD at all. Here is the distinction, with files you can open.

STEP vs STL: mesh or solid

A mesh is a skin made of triangles. It approximates curves and has no idea what a hole is. A solid stores real geometry: a cylinder is a cylinder, with an exact axis and radius. You can measure it, edit it, and hand it to a machinist.

A mesh is a valid file. It is a shell of triangles, with no idea what a hole is. Take one to a machine shop expecting a quote and you will be asked for a solid.

Which one to ask for

• Cutting something flat? DXF. This is what the ai cad drawing generator produces, and the format most cutters want.
• Machining or assembling? STEP. Nothing else is universally accepted.
• 3D printing only? STL is fine, but keep the source, because editing an STL means pushing triangles around, not changing a dimension.
• Sending to a colleague? STEP for 3D, DXF for 2D. Both open everywhere without a plugin.

Why this one writes R12 DXF

DXF has many revisions. R12 is the oldest widely used one and, precisely because it is old, it is the one every laser cutter, CNC controller and CAM package imports without complaint. Newer revisions add features this drawing model does not need, at the cost of compatibility that matters to whoever ends up cutting the file.

Circles are written as real CIRCLE entities and curves as real ARC entities instead of polyline approximations, so CAM software can drive them as true circular moves instead of thousands of tiny line segments.

What is in the files here

Every DXF from this tool uses up to three named layers — only the ones a part actually needs are written into its file. Two of them are geometry you cut. Your CAD package's own default layer 0 stays empty.

Four things worth knowing before these go near a machine:

• Nominal geometry, no kerf. Profiles are true size. Apply cutter compensation and lead-ins in your CAM. On plasma especially, cutting these as-drawn gives holes undersize and outside profiles oversize by one kerf width.
• Bend allowance is not applied. A BEND line marks where to fold, nothing more. No thickness, inside radius or K-factor is used, so a folded leg will come out short by the bend deduction. Calculate the developed length yourself.
• Origin differs by shape. Rectangular parts sit with their lower-left corner near 0,0. Round parts are centred on 0,0. Check before nesting.
• Units are millimetres at 1:1. $INSUNITS is written into the header, but that field postdates R12, so a strict reader may ignore it and prompt you. Answer millimetres.

Licence

Every file in the library is public domain. Use them commercially, in customer work, modified or as-is, with no attribution. Files you generate yourself are yours; nothing is claimed over them.

Look at one

Every file in the library is downloadable. Open one in a text editor: DXF is plain ASCII, and you can read the entity list yourself rather than taking anyone's word for what is in it.