Tuesday, July 8, 2008


I got an interesting comment yesterday with some discussion about one of the emerging low-cost rapid prototyping machines (www.reprap.org).  As with almost all RP machines this one takes input in the form of an STL file.  STL is a plain text format that defines each of the thin layers that compose the object.

Once I get basic Boolean operations running in Wildcat, it should be straightforward to generate STL files.  The basic approach is to intersect the model with a flat plane and get the intersection polygon.  Then move the plane up a bit and intersect again.  Repeat a lot.  So, should be easy, right?

As I mentioned before, I am very busy with my real job this week so I probably won't get much of a chance to work on Wildcat.  I am hoping to finalize the topology algorithm for Pad and then implement early next week.  We will have to see if that holds up.



andyw said...

STL is also the preferred format for conventional 2-, 3- or 5-axis milling or lathe tool-path calculations.

If you are displaying things with OpenGL primitives then perhaps you already have functions for triangulating surfaces and representing curves as a bunch of short line-segments?

I'm slowly working on some CAM-functionality so when that is ready I'd like an interface where the CAM code gets a bunch of triangles as input, and some parameters defining the tool, and then outputs a tool-path in the form of lots of short linear segments back to wildcat

Lampbus said...

Great :)
Actually, I think much work has already been done on the slicing of STL files for RepRap. Driving the machine with differing internal structures for the model, skin thicknesses, layer temperatures to minimise warping is probably best done by the machine driver software.

What we seem to require is a good engineering solids model creator/editor that can generate an STL file.

Deelip Menezes said...

Graham: "STL is a plain text format that defines each of the thin layers that compose the object."

Incorrect. The STL format has nothing to do with slices. A STL file is basically a triangular surface mesh of a solid object. Most CAD systems use the render mesh triangles to output a STL file.

Lampbus said...

yes Deelip, you are right. I was assuming that Graham was thinking of calculating slices to drive the machine directly but now I re-read his post I think he misunderstands STL.
Graham - If you could make STL (triangle mesh) output easily than I would be happy. Im cheering for you and can I get a Windoze version ?