Is there any slicer that can read STEP (or other CSG-CAD) files to produce real circles instead of just linear interpolated patches?
Not the popular ones, but slic3r does have a feature to turn those segments into g-code arc instructions. I’ve never tried that, though.
It doesn’t make sense to go from CSG to polygons and then try to guess what polygons could have been arcs before or are intended to be as they are.
I completely agree with that.
Well, I could be wrong, but according to my understanding, any digital file will produce an interpolated curve. The only difference is that CSG will allow for a much higher resolution because the surfaces are defined mathematically and can be evaluated at an arbitrary resolution (defined by the software being used). When the CAD program exports to STL, somewhere along the line, the software chooses the resolution of the curve. Even the g code arc commands are interpolating at some level.
My solution would be using a program like Blender to smooth things out. Sometimes it can be done with just a few clicks, sometimes it takes more work.
This is my pet peeve with most CAD programs. There is little (if any) control over topology. Many times it doesn’t make a difference. But sometimes it does, especially with organic shapes and when changing file types. It’s just one of the trade-offs when choosing one’s modeling software.
You can interpolate an arc down to the resolution of single step+dir commands of the machine and only the machine controller can do that.
It does that, given a g-code arc.
“smoothing” an STL file will interpolate additional vertices and it will do that to all polygons. Even the ones that have been perfect 90° angles before.
I don’t see it as a tradeoff in modeling software but as a choice of the wrong file format between CAD and CAM software we use for 3d printing.
With subtractive manufacturing you use STEP here. We use STL.
I see what you mean. I didn’t know STEP was used for subtractive manufacturing. Interesting.
Blender does provide control for keeping sharp edges sharp when subdividing surfaces though: http://cgcookie.com/blender/2013/06/21/tips-creating-sharp-edges-modeling/
Substantive manufacturing or milling use just about any format available, also STL.
I think its more about the processing of the geometry needed for printing. For sure STL or any triangle file for the matter is many times easier to process than solid or surface files.
When I started to play with cnc many years ago i stumbled upon DeskProto software for milling and it was the only software at the time who only took STL models, all the other CAM software took all major industries formats and the creator of the software answered the STL’s are much much easier to process.
Id also like to have the option of processing step or igs files, so i get @Marcus_Wolschon idea. Maybe this should be assessed at the creators of slicer’s?