Jack Coats wrote: >First, I know I know not from where I speak, but please correct me: > >g-code - basically a tool path file. this I understand. >postscript - basically a page layout using vectors, and some shapes. >stl - a real 3D file that can be used to define solids but as triangles. > > Right - Actually, I read up a little more on STL (here: <http://en.wikipedia.org/wiki/STL_(file_format)>), and it's apparently capable of describing non-triangular flat surfaces. This capability is apparently never used though, and may not work in any particular piece of software. STL actually doesn't describe solids, it describes surfaces or meshes, which ideally are closed and therefore can represent a solid.
Using STL is perfectly fine for objects that have only flat surfaces. Anything curved can't be exactly represented. So whereas a G2 line can exactly describe an arc segment, an STL file can only represent a piecewise linear representation of that curve. Additionally, the software that converts STL to G-code doesn't know what the underlying feature is really meant to be - it can't necessarily "look at" the shape and generate G-code for "what you meant". (what if you design something with a 300-facet near-curve, not an arc?) STL causes the surface to be sampled three times: first when the original parametric model is converted to triangles, second when the triangles are converted to G-code, and third when the G-code is executed (the machine resolution and timing of the trajectory planner do this). That's one more than without STL, since the G-code and machine sampling will aways take place. As to how bad that makes it, well - you're a better judge than me if you've used a CNC for more than a few hours ;) Unfortunately, I don't know of any other formats that could be used in the near future. There's STEP, which seems to require several appendages to get the spec for, and it would be really cool if someone could just make a machine controller that could read parasolid files (or IGES, or ACIS ...). - Steve ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
