I’ve written a proposal for an alternative paradigm:
- GUI-first, like KiCad - visual modeling is the default
- Text-based source files (YAML/JSON) — readable, diffable, Git-friendly
- Separation of source and result - .step, .stl and previews are built artifacts
- Parametric logic is explicit - slot width = tab width + clearance
Works with Git, CI, or scripting — no more PDM lock-in The proposal is called SplitCAD, and it's just a concept for now — not a working tool. But I’d love to hear from anyone frustrated by the limitations of current mechanical CAD.
GitHub: https://github.com/yuanxun-yx/SplitCAD
ddingus•3d ago
But I am just going to put this here so the general thoughts incorporate a fundamental problem before significant labor investments go too far:
What is a probable, viable, possible answer to the geometry kernel problem?
Parasolid, arguably the leader and generally most capable geometry kernel we have today, is or at least I can't see past...
...is just not something easily duplicated.
There are a bazillion man months of time in that body of code. And those are hard hours!
For those unfamiliar, the geometry kernel is the piece that resolves geometry cases to make operations possible. Imagine a cylinder and rectangle. Now imagine they have some common volume. They intersect, in other words.
Put a fillet on one edge to blend the edge.
How many literal edge and corner cases can you come up with?
There are way more than you think!
Now multiply that tiny problem space with all the geometry used every day.
And then multiple that time again by what it takes to make it robust.
And the whole thing, as it stand today is not even multi-threaded!
Any CAD that we expect to see even moderate general use in a professional sense, needs this piece.
How do we, meaning anyone interested in CAD this way, get past this?
I wish there were some OSS type license for Parasolid. It could be treated like the Linux kernel.
Whatever replaces Parasolid and friends, should be treated like the Linux kernel.
The closest we have is Open Cascade.
Sorry. I do not want to piss on a good vision. But this has to be said.
Peace and good luck!
I used voice input on this. Pleqse forgive typos.
thinkmachyx•3d ago
Although building such engine requires tons of work, but the engine we’re having is indeed a bit of old. Except for the problems I mentioned, you also mentioned they’re still single threaded. That’s why I think it’s still worth building a new one, especially when there’s no good open sourced one currently.
I’m a big supporter of open source. If we have something like that in the future, we should of course make it open source like Linux kernel and allow everyone to enjoy the benefit of it.
ddingus•3d ago
CAD is close to my heart. I jumped in during the 80's as a high schooler running on an Apple 2! Even back then, limited 8 bit CAD could do a lot. And it was one application that helped me see the future! Product design was gonna change as manufacturing already was and the people who knew CAD were gonna be there.
Now here we are, and the CAD companies own design and manufacturing.
I had a flash of an idea this morning reading your comment:
Perhaps we could license Parasolid for a year, or maybe we try what tomfoolery I am about to put here with Open Cascade.
Maybe an AI model of some kind can get us a leg up?
Going back to the fillet example I put here earlier, I want to share a bit of backstory...
I was at SDRC, who had built out a fantastic concurrent engineering and analysis system called I-DEAS. I loved that CAD software and was an applications engineer and trainer on it. Taught many groups of engineers how CAD works, and I got to do that on a system that had collaboration built in from the beginning! Fully revision controlled concurrent engineering and analysis. Fun stuff.
But it died.
My years of skills gone. Kernel could not keep up. So I moved all that onto what is NX today and many of the best parts of the software I loved ended up being implemented because some mergers resulted in the same smart people being product managers! I am particularly redeemed!
And therein lies the lesson of the geometry kernel. You build your true skill on Parasolid systems or risk seeing them lying dormant, cast aside.
The kernel upon which I-DEAS was built was written in Fortran 90. Beautiful software too. It offered capabilities well ahead of Parasolid in some ways, but consistently failed on some common geometry cases that come up rather frequently. Things tangent to things, touching a a point was a big one.
One thing I taught was overbuild or underbuild. Rather than draw a rectangle tangent to a circle to prepare for an extrude, place that end of the rectangle inside the circle and let a boolean operator sort out the two resulting solids.
So yeah, build it kind of wrong so the kernel can build solids. Messy. :)
I was in a room talking to the people who do fillers. Edge blend to some of us.
We talked about my fillet gauntlet. It was a collection of geometry cases that fillet operations failed to complete.
Parasolid could always resolve more of them, and it did that with fairly sloppy tolerances. The SDRC kernel was catching up each rev, but the trend line looked like a decade of analysis of the successful resolutions, and coding for those, wash, rinse repeat a lot.
I wonder if it might be possible to generate geometry cases using parameters such that whole problem spaces could or can be created. Have good kernels solve and train an AI on all that to see what it may then solve differently?
Maybe man years boils down to compute/watt hours?
thinkmachyx•1d ago
The idea of parameterizing geometric problem spaces and learning from how different kernels handle them is strikingly similar to what compiler researchers have done in CS: generating corner cases, analyzing compile errors, and training AI to self-correct. AI coding is used widely in the industry currently, with tools like cursor gaining huge popularity.
And the move to a text-based representation is what makes this all tractable — binary formats never gave us that level of observability or editability. With source-level CAD, it becomes much more realistic to analyze failures, share test cases, and eventually integrate AI tools that can reason about geometry the same way they reason about code.
ddingus•1d ago
Today, a solid consists of the following entities that follow the golden rule; namely, each edge is shared by two and only two surfaces: [0]
Solid Cubish
6 faces bounded by 4 edges each, having endpoints, etc...
Each edge is a curve [1] that lies on the surface so as to bound it to a precision small enough that there are no gaps between the curves and the surface edges they define.
Various bindings and or other data elements:
Centroid
Vertices, each attached to three edge endpoints considered equal given a system tolerance.
...etc.
[0] Where an edge is alone, the resulting non manifold has a hole in it somewhere, and or is a surface body where a large number of edges stand alone.
Where an edge is shared by more than two others, that is a self-intersecting body.
Neither case is actually manufacturable. One can understand a lot just from edge checks too.
All edges alone, or unique = face.
No edges present = closed surface must be sphere, torus or elliptical solid body
...etc.
Also, in wireframe NURBS curve land, the most useful thing about the decision to represent all the analytic entities (line, arc, conic, hyp, parabola, circle, elipse...) as NURBS was to be able to reason programmatically with far fewer pain in the ass cases!
Eg: a trim function can be written to process any NURBS arguments. One that has to face lines, circles and friends ends up either converting to NURBS or handling trim line to circle, arc to conic, NURBS to ... you get the idea. Too messy.
Generating that data won't be cheap, but it can be distributed! If we had a few thousand users run scripts on their systems, we could get a large problem-solution data corpus.
[1] In modern CAD, everything is a curve. Lines are NURBS curves having only two control points. Earlier CAD actually used all the entity types directly, not just deriving them on the fly from the NURBS.
Arcs are curves with 3 specifically placed control points.
Hyperbola, Conic, Parabola, are the next order up, 4 control points, and above that is the Bspine. 5th degree, and above curves.
Why can't we tokenize those things and train some LLM like thing? I am going to ask my data science friends about this. Has me thinking!
At the core, it is all NURBS curves and surfaces. Those two can represent all that we need.
The relations are all just text, names of entities and how they are related.
Even the NURBS surfaces have text forms. At one point, some systems would let a person just define one by typing the U, V points / matrix values in.
Eg:
Plane [point 1, 2, 3...]
That data is where both the problems and answers are, in this training sense anyway.
How can it not?
What I put before was basically the idea of generating a case, say conic section and cube/rectangle.
Generate common volume case 1 in modern kernel and output text representation of it. That exists today.
Then generate ideal edge blend solution 1, and minimum radius case 1, maximum radius case 1.
Output those and we have in text:
Problem case 1 of problem space 1.txt
Ideal, or common edge blend solution.txt
Max radii case 1.txt
Minimum radii case1.txt
Then proceed to generate a bazillion of these, until the problem space of a conic section intersecting a rectangular body is represented fully enough for AI models to operate and even potentially demonstrate emergent behavior like they do on text and code today.
Edit: basically an LLM like thing becomes the kernel and the CAD system is how one talks to it. Not sure that came through before. Writing it out just in case.
And to be fair, I am still learning in this area. If what I put here is a no way, it would be most helpful to tell me or link me to why not. Thanks in advance.
Edit: Ahh, I see. Lol, read in the cad code and have an AI rewrite it? Maybe, but doubtful.
A bounty on... um yeah. 'Nuff said.
ddingus•23h ago
kingkongjaffa•11h ago
Their link is just AI slop there’s nothing insightful here: https://github.com/yuanxun-yx/SplitCAD
Be wary/careful if they reach out to you some way.
ddingus•10h ago
kingkongjaffa•7h ago
Like a human might say “cheers for the thoughtful response” and an LLM would say something more like this “Thanks a lot for the thoughtful and respectful reply! I really appreciate that you raising the engine issue without dismissing the whole idea. ” The tell here is that it’s maintaining a polite engaging conversation while mirroring the semantic meaning of your reply without any conceptual depth.
You could have written anything and it would have agreed with you.
Anyone who has spent a few minutes genuinely thinking about how to build CAD can easily see that the geometry kernal is the crux of the problem and why open source attempts lag behind commercial CAD.
But the LLM user response here is overtly neutral essentially saying “thanks for raising this super obvious thing”
Its being overly polite. In another comment they say they are “honoured to have your reply” which again is just overly polite.
On a 3 day old account it just stinks.
OP is either a low effort poster farming for something or an english as second language user relying on an LLM to write for them way too much.
Or they are a naive user who wrote a low effort LLM generated proposal without looking at any of the prior art of the topic.
ddingus•1d ago
Humor mode = 1 (you will see why)
LOL, Thanks for that! Really. CAD is kind of obscure meaning it is rare to have this chat. Was nice.
I find it an equal honor to talk with others very highly skilled.
Bromance Curious Mode = 0
Cheers!
thinkmachyx•20h ago
kingkongjaffa•11h ago
loloquwowndueo•3h ago
layerdynamicsai•2h ago
Doesn’t that come down to the precision, 1.e-7?
blobfish01•2d ago
ddingus•1d ago
Sidebar: My home plasma TV is a 3D capable one. Back in the 90's I used to use 3D to visualize models on SGI machines.
Fast forward to the mid 10's and I can hook up a laptop with nVidia GPU and run NX and the whole interface and model works in 3D!
Amazing. I love it, especially with a space controller.
There are maybe a handful who do that on even a very low basis.
That has always bothered me. Part of me knows some people have trouble and that another part knows the development gets even more expensive, but still your point is a solid one.
blobfish01•1d ago
ddingus•1d ago
Don't be sorry. Tons of users call it UG. Yeah, I had an airplane model to play with and built a fair number of surfaces.
It works well. Space X has a nice 3D setup.
api•4h ago
Of course the catch here is going to be the precision required for real world use. A ton of impressive AI demos are just that — demos. They are good enough to wow as a demo. Still, if the data set is big enough, and you’d probably want to run the model itself in at least fp32 precision, maybe you could get something.
There is a body of machine learning work that’s been done on precision annealing of models. Basically you train to min loss and then go into a finer grained domain using something like simulated annealing to fine tune parameters.
zihotki•4h ago
tda•4h ago
> Whatever replaces Parasolid and friends, should be treated like the Linux kernel.
So much this! But the undertaking is so daunting, how do we get there? A capable, OSS CAD kernel would provide so much value to the world. I whish e.g. the EU could just "nationalise" such important, crucial software and redistribute it openly. Or that through some Chinese effort a newer and better kernel just lands out of nowhere and disrupt the field, like with DeepSeek.
The world has benefitted so immensely from Linux being freely available, has anyone even tried to put a price on the benefit to humanity? Imagine being stuck in a world where on big corporations can have proper OS-es, and everyone else is stuck with some anaemic locked down kernel...
cyanydeez•3h ago
Will need to clear put billionaire parasites, and that wont happen till American fascism hita its nadir.
rjsw•4h ago
I did propose that licencing it as dual AGPL + commercial could be a way around the objections to the attempts to make JT into an ISO standard, didn't get anywhere.