DXF export for laser cutting shops

[plazmabokor]

Hi Stefan,

The SVG export already says it is for laser cutters and plotters, and it works well for a hobby laser. Industrial laser cutting shops, though, usually ask for DXF, so today a user has to convert the SVG in Inkscape first. I need this for my own parts, and it will help everyone who has sheet parts cut by a shop.

Proposal

• A DXF choice in the export window, next to SVG, with the same View options: silhouette, footprint and visible edges from above.
• The same outlines the SVG export already makes, written as closed polylines in millimetres, one layer per body (or per colour), as plain ASCII DXF that common CAD and laser software can open.
• Like the SVG, curves would be short straight segments, not true arcs. That is fine for most laser software; recognising arcs and circles could be a later step if someone needs it.
• No DWG: it is a closed format, and DXF covers laser cutting.
• Guide text, the export window texts in the languages, What's new card and unit tests (a round trip of the outlines, millimetre units), as with the reference image.

Questions

1. Layers per body or per colour?
2. Only the SVG views, or also the 2D drawing and the section view as DXF?

Thanks!

[henmedia]

@plazmabokor thank you, that is a good idea: a shop that cuts sheet parts asks for DXF, and the SVG detour through Inkscape is a hurdle. I'd like to see it the way you describe it: same views as the SVG, closed polylines in millimetres, no DWG. To your questions: layers per colour sounds better to me, since a shop sorts cutting and engraving by layer and colour, and one layer per body would be too many on a larger sheet. And only the SVG views first, the drawing and the section could come later.

Do you plan to build it yourself, as you did with the other features? I'd much prefer that: you work with laser cutting shops and know what the file has to look like, and you can check the result in their software far better than I can, since it is not an application I use myself. A pull request is very welcome.

[plazmabokor]

Thanks, Stefan, and yes, I'll build it. Please don't start on it yourself for now, so that we don't do the work twice: I'm talking with laser cutting people (a shop that works in ZWCAD, and someone with a CO₂ laser) and want their feedback on a sample file first.

What we found so far changes parts of the plan, both my first proposal and the layers per colour:

1. Real arcs and circles, not short straight segments. Laser controllers dislike curves made of many tiny lines: the head shakes and the edge gets worse. Several shops accept only LINE, ARC and CIRCLE, no polylines, splines or blocks. So the export will turn the outlines back into real circles and arcs. For holes and rounded corners this is exact, since the points lie on the true circle. Free curves such as text get fitted with arcs within about 0.01 mm.
2. One layer, one colour. Shops read the colour as the process (white = cut, yellow = engrave, blue = bend) and ignore other colours, and they want everything on layer 0. A layer per body colour would put cut lines in colours a shop ignores. The people I talked to confirmed it: one colour. So all cut contours go on layer 0 in colour 7 (white).
3. Units. DXF R12 has no unit field, and some programs read it as inches. So the file will be DXF 2000 with $INSUNITS set to millimetres.
4. Clean contours. Every contour exactly closed (one shop counts a 0.01 mm gap as open), no doubled lines where two bodies touch (they get joined first), not mirrored, Z = 0, 1:1.
5. Views. Only silhouette and footprint: the visible-edges view would turn inner edges into cuts.

I have sent a sample DXF built this way (lines, arcs, circles; layer 0; colour 7; mm) to the shop. Once they confirm, I'll build it in layerling, test real parts from layerling with them, and then send the pull request.

[henmedia]

@plazmabokor thank you, that all makes sense, and what the shops told you is much better than my first idea: real arcs and circles, one layer, one colour, millimetres in the file and no inner edges. I will leave it to you and not start on it myself.

[plazmabokor]

Hi Stefan,

The DXF export is done and tested here: lines, true arcs and circles on layer 0 in colour 7, DXF 2000 in millimetres, not mirrored, bodies joined so every contour is closed and no line is doubled. The files pass ezdxf's audit, fillets come out as exact arcs, and free curves like text stay within 0.01 mm. The shop can only try it on a laser cutter next week. If you'd like it now, I can send the pull request right away; otherwise I'll send it after the cutting test.

It would also make sense to do the import: with export only, layerling can hand a DXF to a shop but cannot open one that comes back from it, or a part outline from a supplier. I'm going to start on that too: DXF into a sketch body, the way SVG comes in, keeping lines, arcs and circles exact.

How would you like the two: in one pull request, or separately (export first, then import)?

[henmedia]

@plazmabokor thank you, that is a lot of work done, and the tests with the shop are what I trust most. Please send them separately: the export first, then the import in its own pull request, so that each one is small enough to read well. Please send the export pull request now, I'll read it while you wait for the cutting test.

About the release: I would not mind to publish the export before the cutting test, with a clear note in the guide and in the release that it is not tested on a laser yet and that feedback is welcome. What do you think: is that fine for you, or would you rather wait for the shop's result? You know the shops and the risk better than I do, so please give me your assessment.

[plazmabokor]

Thanks! Separately it is: the export pull request is #782, the import comes later in its own one.

Releasing the export before the cutting test is fine with me. The risk is small: it touches nothing else in layerling, the files pass ezdxf's audit, and they follow the rules the shops publish. The guide row and the What's new card already say it is not yet tried on a laser cutter and that feedback is welcome. I'll report the shop's result here next week.

[henmedia]

@plazmabokor thank you, I read the pull request: the file structure, the arc and circle fitting and the tests look good to me, the tests pass here as well, and I have no changes to ask for. Fine with me to publish the export before the cutting test, with the note that it is not tried on a laser yet. One small thing: the guide row is in eleven languages, but not in Danish, Arabic, Brazilian Portuguese and the two Chinese ones. If you want, add it there too, otherwise I will leave them as they are. Please tell me what the shop says next week.

[henmedia]

@plazmabokor the DXF export is out in 1.104.0, with the note in the guide and the card that it is not tried on a laser cutter yet. Thank you for the work and for the tests with the shop. "Save to the server" works for DXF as well.

[henmedia]

@plazmabokor your DXF import (#792) is out in 1.105.0, together with the fix for circles and arcs on wobbly outlines in the DXF export, so a DXF can now go to a shop and come back again. Thank you for both, and I'm looking forward to what the shop says about the cutting test.