CAD Sketcher, free and open-source project bringing CAD like tools to Blender3d

I suspect that having a generic meshing algorithm that will always mesh your datastructure with no edge cases would significantly reduce the time needed to implement a CAD kernel. You just need an algorithm that can tell you if a given point is inside or outside of your BREP. All you really need for that is a surface that points at a given direction, and the ability to tell whether a point is under the surface or not. Define your surfaces as BREP, render them using SDF, only have to write one meshing algorithm.

That being said I disagree with your definition for parametric CAD. Mostly the name, I get that you're talking about BREP based CAD. That is one way to do parametric CAD, but CSG can also work, especially if you can do more advanced operations like a filleted difference or union, or blends between two shapes, or other advanced CSG operations. I don't think that CSG-based CAD is inherently worse as long as you've got the ability to do things like fillet/chamfer CSG operations.

You probably don't need to do a fillet along an edge if you can do a fillet where you subtract one object from another, something that SDFs can do easily: https://github.com/fogleman/sdf#smooth_difference

That said, you can e.g. calculate derivatives of the SDF and, simply speaking, when they 'flip' you know you found an edge or corner. You can project onto the SDF along a plane or line and 'record' the intersection, use it as input in your model etc.

Similarly, you can treat an area bounded by such edges as a face etc.

Just because there is nothing out there yet doesn't mean it can't be done.

I also predict a great future for SDF based CAD for the simple reason that manufacturing methods mostly used for prototyping now (3D printing) will become more common for final pieces.

And there is no need for an explicit representation (higher order surfaces or polygon meshes) of the shape to get tool paths (often derived from 2D bitmap slices) for these methods.

In my uninformed opinion working with meshes is hard. In the interest of comparing apples to apples I'll compare a CSG-based approach (joining two mesh objects together) with an SDF-based approach (joining to SDF objects together).

If you want to merge two mesh spheres together you need to do a lot of work. First you need some way of telling whether a point is inside or outside of another mesh. This is because you need to be able to delete all the vertexes/points/faces that are inside the other mesh. So you do that, and you delete all the points/vertexes/faces that are colliding with the insides of another object. Then you need to stitch the two meshes together. This is a whole thing, you need to find the boundary where the two meshes would have collided, create a bunch of new edges along that path while also taking into account where the existing faces on both objects are going to be.

There's a lot that can go wrong during this as well, it's possible for your geometry to be "non-manifold" which means it has no clear inside or outside, and it's really easy to accidentally make an object non-manifold when you're stitching it together with another object. There are issues where sometimes meshes look alright but in reality there are two edges on top of each other, or a face with zero area, or all kinds of crazy stuff. Making a tool that can reliably stitch two meshes together is a pretty big challenge. Than you start talking about adding fillets to vertexes, and how that affects the mesh geometry of other attached faces, and you're having to write some really complicated error prone code for N different combinations of situations. Like what if the chamfer abuts another chamfer? What if it abuts a spheroid? A bunch of edge cases (heh) depending on the faces that your edge butts up against.

With SDFs you just check if the point is inside one object or the other, and than re-generate the mesh from scratch. You write one not-too-difficult mesh algorithm and everything else is basically just OR/XOR/AND-ing things together. It makes defining geometry geometry about as simple as possible, just write a function that can say whether a point is inside your geometry or not. Something you need to be able to do for mesh based CSG anyway, but with a bunch more complications.

This is also why tools like openscad can't do fillet/chamfer joins after 10 years and the tool I threw together in a few weeks can.

https://github.com/traverseda/PySdfScad

I am a robotics engineer and 100% of my work is open source (see my profile). I understand that without fully open source CAD it is hard to make fully open source machines.

If we were somehow able to rally support around a single project to create an open source CAD kernel and associated interface (perhaps built in to blender or FreeCAD to avoid building a new UI), what approach would you recommend? How long would you estimate it would take for three full time senior developers to get a useful system out?

Any thoughts are appreciated. I am at the extremely early stages in my career where I hope to learn to raise money for open source non profit hardware projects. Open source CAD is a sort of linchpin and without it we cannot succeed in quite the way we would like.

I also realized during that time that my distro was doing a poor job at packaging it to make it work as designed (and I can't fault the packagers for that, it's a highly specialized/niche application after all). The flatpak version seem much more cohesive.

If one thing, I'm amazed by how much one can accomplish with FreeCAD given a little patience and perseverance: it brings parametric CAD, drawing projections FEM… to the masses, which, when I was learning that stuff as part of my curriculum, was completely out of reach of most universities, let alone the hobbyist scene.

It's an under-appreciated, fundamental, piece of software if you ask me.

With basic access you can still: View projects Comment on and mark up files Download files

It used to be you had to switch every year. But the ts and cs are buried on the web site if they are public at all. You have have it installed to see your license details, which I no longer do.

You should try solvespace, it has that fun feel but let's you apply constraints directly on the sketch.

You make a base sketch and pad it up to create a square part with a single hole in the centre. You chamfer the hole. You change the base sketch so that it is now a rectangular part with 2 holes, 1 at the left and 1 at the right.

Should the chamfer apply to the left hole, the right hole, or both holes?

Obviously there are special cases that FreeCAD doesn't currently handle optimally, but a general solution is impossible without FreeCAD reading your mind.

(You could also asy "any of those 3 options is better than trying to apply the chamfer to a random bit of un-chamferable geometry". But a general solution is still impossible.).