I'm on a bit of a crusade to persuade designers of open-source models to include their original CAD models.
There seems to be a trend of including a STEP file and calling it a day. While that has uses, it is only a partial solution and does not represent the "source code", so arguably an open source design must have the original CAD model included.
I am aware that to some people this may appear as if I am being "ungrateful" and truly that is not the case. I am grateful for all the wonderful free models. I am, though, enthusiastic about the idea of remixing, improving, and building upon those ideas. I suspect that many people think that the STEP file is enough for this, but it really isn't, for several reasons.
- STEP is not the "source code". It is as a PDF document is to a Word document. It is fine for sharing verbatim copies of a model, but not really suitable for editing. Like a PDF file, it is possible to edit, but really you need to edit the original document.
- A CAD model contains a lot of information that is missing in the STEP file. I use F360 so I will use concepts from that. F360 captures the design timeline, including 2D sketches and all the operations carried out to reach the final model. It allows sketches to be edited, operations to be re-ordered, inserted, modified or deleted. It also contains user parameters (in parametric designs) and all the exact dimensions of each body and operation. It contains the hierarchy of components that make up the complete object. All of this information is missing (or at least hard to get to) in a STEP file. The design timeline and component structure is key to editing in F360.
STEP exports are good when you need to include componets from one model into a different model, or into a different program. For something like a stock part from a manufacturer's catalog, that you never want to edit, STEP is perfect. What it is not good for at all is "remixing", changing or improving a design.
So why don't people publish their original CAD models? I can think of two reasons.
- A desire to "keep control" of the design and not have others change it willy nilly. That decision is up to the designer, but in my view that's not "open source" because you haven't shared the source. The source is not open. STEP files are not source code and neither are STLs. Both represent (in software terms) the compiled binary. How many designs are there on Thingiverse with a so-called "open culture" Creative Commons license, but which don't contain the "source code"?
- They are for some reason not very proud of their work. I have had this reasoning given to me a few times, usually in the form of "the CAD file is a bit of a mess, I'll clean it up and maybe release it later". Nobody ever (well hardly ever) cleans up their work later. It is just too much to expect. Perhaps they think they will be criticized by the community. Newsflash: most CAD files are "a bit of a mess" including most of mine. Most of us are not professional 3D modellers or mechanical engineers so this is not surprising. I would say to these people, "no matter how bad your CAD model is, it is still better than no CAD model".
Opinions? Discuss...