I started using Inkscape, a sweet open-source vector graphics program, to produce (and/or steal from the internet and convert) designs suitable for carving on the CNC as Inkscape has a plugin to export the file as a .DXF. Converting some files, I discovered the current export script does not correctly handle all types of transforms, so some parts of the file may export out-of-proportion to each other or in strange size units regardless of the drawing units of the original drawing (Inkscape’s internal drawing unit is apparently equal to 1/90 of an inch, wait, wtf?). Also, if the drawing contains curved (Bezier) lines, these will be exported more or less as-is (DXF splines) and many free/cheap/itch-scratch-ware programs will not handle the resulting file (since the ‘correct’ representation or interpretation of splines is never disclosed in the published DXF file specifications, so everyone kind of does them in their own way, with less-than-stellar results).
Bob Cook noticed these limitations and updated the script to fix many of the ‘unusual transforms’ scaling issues, and convert Beziers to standard polylines that any program will import. It also adds some support for layers, including special ‘drill’ layers whose drawing objects will be output as single points (no lines) for hole drilling.
In theory, the layer support as he implemented it ought to work (it’s correct and in conformance with the DXF spec, which allows drawing objects to be assigned to arbitrarily-named layers throughout the file). In practice, many of the same free/OSS, low-cost and weekend-warrior tools do not handle this any better than splines. I dug up a copy of the DXF spec, played around a bit and found that these programs expect all layers to be formally declared in a DXF LAYER table in the header section of the file before use. So here is an update to the export script that generates a proper LAYER table, allowing a wider variety of toolpath generating programs to import them correctly. So far it has been tested with ACE Converter and CamBam and seems to work well, but as always this is a quick n dirty, not exhaustively tested script and there is no lifeguard on duty. (Inspect the imported files for problems before commanding your big machine to cut them!)
Better Better DXF Output for Inkscape
Just unzip into your \Inkskape\share\extensions directory. Note that the updated ‘simpletransforms.py’ replaces an existing file.
Note: There is still an outstanding issue with Grouped objects in Inkscape being exported with incorrect size. As I understand it (assuming the document structure sent to export scripts is substantially an SVG file), transforms are applied at the Group level, which is sort of a container that has the actual drawing objects (and possibly further nested groups) as its children. Guessing that to handle this correctly, rather than looking for transforms at the node itself, it must also maintain a stack of transforms that have been applied at the node’s parent level, and parent’s parent, etc. For now, it is an easy workaround to ungroup everything before export. Maybe someone with freetime can update this and release it as ‘Better Better Better DXF Output’ :-) (b3dxf?)