Compatible file types

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The most common file types for drawing data (or CAD data) are DXF and DWG. The DXF (Drawing eXchange Format) file format is a public standard that is published and available to all developers. The DWG (DraWinG) file format is proprietary to the company that creates and sells AutoCAD. This has not prevented other developers from writing programs to read and translate DWG files, but it does make their job harder.

Of course, each developer likes to “improve” the standard and many of them will add these improvements to their version of the file. This can cause problems when you try to read a DXF file written by Developer A (with all their improvements to the format) using a program from Developer B (and all their improvements).

Fortunately, it’s not total chaos, and for the most part isn’t particulary confusing. But you can take some steps to make sure that the file you create can be read accurately by the person you’re giving it to.

  • AutoCAD Release 12 DXF files are widely compatible
    Newer versions of the AutoCAD DXF file are less likely to be supported. Generally speaking, the newer the format, the less compatible it is. If you have a choice when you save the file, choose the AutoCAD 12 DXF version.
  • Avoid “binary” dxf files
    Virtually nobody supports binary DXF files
  • Explode or ungroup all entities
    Before saving as a DXF, “Explode” all entities that define the geometry of the part. Most CAD programs let you group together entities to make it easier to copy and move them. Be sure to explode (or “ungroup” or “convert to curves”) before saving the DXF file.
  • Use simple lines and arcs whenever possible
    The DXF file format doesn’t support Bezier curves or other fancy (and convenient) ways of creating complex curves. When you export the DXF file, they will be translated and might not turn out the way you want them to. The best thing is to start with simple lines and arcs which are exported exactly as they appear.

You may find that your drawing program does not allow you to “Save” the file as a DXF. Most likely, there is another command such as “Export ” or “dxfout” that will do the job.

If you have trouble reading a file after it was emailed, then ZIP it up first, using a program such as WinZIP or PKZip. Some e-mail programs will alter DXF files as they appear to be text files that can be formatted.

Document your file

You can also make sure that you include documentation when you send your file to somebody who will be making your part. This will help make sure that you get the part you think you will get.

  • Provide a print-out, with dimensions, so the programmer can check the file conversion against known geometry and dimensions. The units of a DXF or DWG file are sometimes ambiguous, so the part will likely import at the wrong scale. (In fact, the DXF file format doesn’t include dimensions at all.)
  • Draw two concentric squares on each drawing that you send. The outer square should have a dimension of 1″ x 1″, and the inside square should have a dimension of 1 cm by 1 cm, as in the picture below:

1 inch square drawn for scale

Whoever you give the drawing to can quickly see if the drawing is properly scaled by simply measuring the edge of one of the squares. This will prevent mistakes such as cutting a part that is 25.4 times too big due to some metric conversion problem. (The tiny text underneath the 1 cm square says, “Note: If the dimensions of this box are not what is specified, then this drawing is not to scale and should be re-sized accordingly.”)

Tip: If the file will eventually end up on an OMAX system, then you can use the “Layers” in your CAD system to specify cutting Quality (Layer 0 is for heads-down traverse, 1-5 are Qualities 1-5, 6 is “etch”, 7 is “scribe”, 8 is “water only”, 9 is for leads, 10 is for “heads-up traverse”, and 11 is for “Minimum Taper.”