I've used OpenSCAD for years and kept hitting the same walls, so I built exact CAD modelling for GNU Octave
OpenSCAD has served me well, and I still think its idea is right: a part should be a program, not a pile of mouse clicks. But a few of its limits kept biting me:
- **Everything is facets.** A cylinder is $fn sides, so its edges can't be rounded after a boolean, and the part reaches a CAD program as triangles, never as a true cylinder.
- **No fillets or chamfers on the edges you actually have.** Rounding the result of a difference means minkowski or a library trick, and it gets slow.
- **You can't ask a shape anything.** Not its volume, not its size, not where its edges are, so a script can't adapt to its own geometry.
- **No STEP**, so a part can't go to a machinist's CAM or a colleague's CAD with its geometry intact.
- **The language is small.** No real data structures, no numerics, no plotting, so computing anything, a gear profile, a cam, a stress estimate, happens somewhere else.
I'm a GNU Octave developer, so I built the thing I wanted as an Octave package, **drafting**, on top of Open CASCADE, the kernel FreeCAD and CadQuery use. Version 0.2.0 is out today.
Here is the classic CSG example, the cube and sphere with three bores, rebuilt:
body = intersect (solid.box (15, 15, 15, 'Anchor', 'centroid'), solid.sphere (10));
c = solid.cylinder (5, 20, 'Anchor', 'centroid');
S = subtract (body, c, rotate (c, 90, [1, 0, 0]), rotate (c, 90, [0, 1, 0]));
F = fillet (S, edges (S, 'Type', 'circle'), 0.8);
write (F, 'csg.step');
write (F, 'csg.stl');
The fillet line is the one OpenSCAD can't do: the bores' rims are exact circles, so edges finds them by type and `fillet` rounds them. The result goes out as STEP with its curved faces kept, and as STL for the slicer.
What you keep from OpenSCAD: the part is a script, the booleans read the same union, subtract, intersect, and hull, resize, mirror, text and linear and rotational extrusion with twist and scale are all there. A tutorial for OpenSCAD users maps OpenSCAD's words to the package's, one by one.
What you gain: shapes are values in variables, so a function returns a part and a loop builds an array of them; holes with counterbores and countersinks; shells; lofts and sweeps along 3-D paths; sections that are exact outlines you can extrude again; volume, area and bounding box; assemblies saved to STEP and 3MF with names and colours; and technical drawings to DXF and paper, with dimensions. And it's all inside Octave, so the maths that shapes the part sits in the same script.
Honest limits: it builds on Linux only for now, from source, against Open CASCADE's development packages (one `apt` line on Debian or Ubuntu). There's no editor with a live preview; you call `show` and the viewer window redraws. Windows and macOS are on the roadmap.
- Guide with twelve tutorials: https://pr0m1th3as.github.io/drafting/guide/
- Repository: https://github.com/pr0m1th3as/drafting
I'd really like to hear from OpenSCAD users: which of your models would break first, and what you'd miss.