How to prepare a DXF file for laser cutting: a practical guide

Why file quality matters

In sheet metal laser cutting, the DXF file is not just a reference drawing: it is the path the machine will follow. From that file we derive the cutting length, the number of laser pierces, the part’s overall dimensions and its surface area — all the data that determine time, weight and cost. A well-prepared file produces an instant, reliable quote; a file with errors can produce a wrong price or a part different from the one you had in mind.

The good news is that the most common mistakes are few and easy to avoid. This guide lists them in order, from exporting out of your CAD to the final check before uploading.

1. Units and scale

The drawing must be exported in millimetres and at 1:1 scale. The DXF format contains information about the file’s unit (the $INSUNITS variable): if it differs from millimetres, the calculator converts the dimensions automatically and warns you. Some reused drawing templates, however, contain a wrong unit left over from earlier versions: for this reason the system discards clearly absurd conversions, but the safest solution is still to export in millimetres.

After uploading, always check the overall dimensions shown in the preview: if a part measuring 200 mm comes out as 20 or 5080 mm, the problem is almost always the export unit.

2. Only the part profile

The file should contain only the geometry to be cut: outer contour, holes and slots. Everything else should be deleted or moved to a separate drawing:

• dimensions and text: they are not cut and the calculator ignores them;
• title block and drawing frame: a rectangle around the part could be mistaken for a cut. The system recognises the typical case of the sheet frame and excludes it, but it’s better not to rely on this check;
• centre lines, hatches and fills: remove them, as they are geometry that doesn’t correspond to a real cut;
• multiple views of the same part (plan, elevation, sections): the cutting DXF only needs the flat pattern.

3. Explode blocks

Many CAD programs group geometry into blocks (in DXF they appear as INSERT entities). The calculator works on elementary geometric entities and ignores blocks, with a warning: if your part is contained in a block, the quote would be empty or incomplete. Before exporting, explode the blocks so that the profile is made of lines, arcs, circles, polylines, ellipses or splines.

4. Closed contours and connected segments

The outer contour and every hole must be closed: the last point of each profile must coincide with the first. The contour doesn’t need to be a single polyline, because the calculator reassembles profiles made of many segments (lines, arcs, splines) into one chain, as long as they touch at their endpoints. But if even a small gap remains between two segments, the chain is broken.

What happens when a contour is not closed:

• if it’s the outer contour, the part’s area (and therefore its weight and material cost) is overestimated from the bounding box, and a warning tells you so;
• an isolated segment, not connected to any other geometry, is excluded from cutting: if it was a real cut you forgot, it will be missing from the quote.

Most CAD programs have commands to join segments (such as “Join”) and to check whether a polyline is closed: use them before exporting.

5. No duplicate or overlapping lines

Duplicate lines on top of each other are invisible on screen, but the machine would read them as two cuts along the same path. As well as lengthening cutting time, they increase the length counted in the quote. Almost every CAD has a command to delete overlapping entities (for example “Overkill” in AutoCAD): it’s good practice to always run it before exporting.

6. Bend lines

If the part also needs bending, the file must contain the flat pattern, and the bend lines must be drawn with a dashed linetype (HIDDEN or DASHED). This is the convention SolidWorks uses when exporting a sheet metal flat pattern, and it’s the one the calculator recognises to tell a bend from a cut. A bend line drawn as a continuous line would be interpreted as a cut to be made.

7. Punching operations

Countersinks, ventilation louvers and stiffening ribs can’t be deduced from a 2D profile. These operations use three dedicated layers (SVASATURE, GRIGLIE, NERVATURE), described in detail in the site’s DXF guide to punching.

8. File format and version

The calculator reads DXF files in text (ASCII) format, which CAD programs offer by default. If you have a DWG, save it as DXF from your CAD program. If you start from a 3D model, you can upload a STEP file directly: for flat sheets or parts with a single bend, the flat pattern is derived automatically.

Final checklist before uploading

1. Is the drawing in millimetres and at 1:1 scale?
2. Does the file contain only the part profile, without dimensions, text, title block or extra views?
3. Have the blocks been exploded?
4. Are the outer contour and all holes closed?
5. Have you deleted duplicate or overlapping lines?
6. Are bend lines dashed (HIDDEN or DASHED)?
7. After uploading, do the overall dimensions in the preview match the real part, with no warnings left to check?

If the calculator shows a warning you’re not sure how to interpret, don’t confirm the order: contact us with the file and we’ll check it together.