Could you point me to some open source/free CAM tools that will do 3D cam from a .stl file?
My understanding was that most 3D cam was done with heightmaps. A .stl isn't a heightmap.
To be technically correct, you're describing 2.5D milling not 3D. 3D CAM can't be done with a heightmap, because a heightmap only represents displacement perpendicular to one plane. The Shapeoko is only capable of 2.5D milling. But, yes, it's very common to use heightmaps to generate 2.5D toolpaths. It's also common to use vector graphics (SVG) and mesh data.
BlenderCAM is free and it does work well enough to generate parallel and contour toolpaths for triangle meshes. It's also still a work in progress, so don't expect it to do everything you want. I've used it to do some test engravings in styrofoam with good results, but haven't tried it for a "real" job yet. Take a look at the BlenderCAM gallery
to get an idea of what it's capable of with a little practice and effort.
I've heard good things about FreeMill
, but haven't tried it myself. It's capable of reading STL files. There are many other options out there. Check out the wiki's CAM Software page
for a list.
I'm going to back off a bit from my previous sentiment... I don't really want to turn you away from the idea of converting a 3D mesh to a heightmap, because it does have merit. I can think of a couple of reasons why one would want to do this. For instance, a heightmap is easily modified and blended with other heightmaps to create compound surfaces that would otherwise be difficult to generate in Blender or another 3D modeling program. Heightmaps can also be "locally scaled", meaning that dimming selected pixels produces a scale transform just in that area without affecting the rest of the model, which is an operation that can sometimes be difficult to perform in modeling programs.