Build123d: A Python CAD programming library

59 pointsposted 21 hours ago
by Ivoah
(github.com)

20 Comments

injidup

3 hours ago

These types of CAD scripting tools are great but always try to position themselves as an “alternative” to GUI-driven CAD, whereas in reality they are complementary. OnShape got it right with FeatureScript (https://cad.onshape.com/FsDoc/ ), which provides a very similar experience to Build123d at the scripting level. However, the insight that OnShape got right is that these scripts automatically become available as possible nodes within the history-based modeller. The OnShape UI is infinitely extendable beyond the fixed set of tools that comes with the base modeller.

Build an FOSS CAD front end using something like Build123d as the extension engine, and then add hooks so the user can select edges, surfaces, objects, etc., and feed them to inputs on the scripts. The output of the script is then the new state of the history-based modeller. That would be killer

CountVonGuetzli

2 hours ago

I didn't know OnShape had such a feature. Will check it out!

What you describe is one of the main reasons why I use Rhino3D. It can be scripted via the Grasshopper plugin, which integrates really nicely with Rhino and its primitives. Sadly, Rhino isn't open source and is quite pricy

- https://www.rhino3d.com/ - https://www.grasshopper3d.com/

injidup

2 hours ago

The fun thing is that onshape itself has a very thin kernel. Most of what you see as built in features are actually featurescript based. Onshape provides the source code for their built in feature set as a reference. https://cad.onshape.com/documents/12312312345abcabcabcdeff/w... You do need an account login ( free ) to view it.

aaronblohowiak

30 minutes ago

Kernel here is ambiguous.. I get what you mean, but parasolid is usually the thing described as the cad kernel.

injidup

a few seconds ago

You are right but I also kind of did mean it that way. I believe that Parasolid is at heart of Onshape, the true kernel. Then on top of that is a compatibility layer describing the set of low level operations available to featurescript. I'm sure that not everything in Parasolid is available to featurescript and perhaps there are some things added that are not in Parasolid. Featurescript also contains the selector/query logic for programatically picking geometry. Whether that comes from Parasolid I am not sure. I haven't worked with featurescript for a number of years now but when I did I was amazed. I managed to make an operation for taking any solid from the UI and generating customized interlocking ribbing. The idea was hollow surfboard design. It worked and I left it at that. Never built the surfboard!

However the downside with featurescript and I think a big mistake on their part was to use a custom language rather than python or javascript. Featurescript is almost javascript but with some syntax changes and magic DSL's. You are also forced to use the inbuilt editor which is horrible and if you have burned VIM keybinding into your nerve endings, going back to non modal editing is horrible.

alnwlsn

an hour ago

I think most GUI CADs have some kind of API like this. In FreeCAD it's Python. In Solidworks, it's VBA or C#. I don't think any are particularly well documented or supported by tutorials.

rao-v

2 hours ago

I’d love to see this. It was a frustrating learning curve for me to realize that I couldn’t STEP export work from OpenSCAD to something like Fusion.

Build123d is much better (supports STEP export and import) but a tightly integrated CAD frontend would be ideal!

Tagbert

3 minutes ago

I used to do a lot with AutoLisp in AutoCAD back when it ran in DOS. Did a lot of dynamic creation and manipulation of the models with it. It was useful and a lot of fun (aside from parenthesis nesting).

nakedneuron

2 hours ago

as someone mentioned recently somebody made this build123d-playground on the web:

https://jojain.github.io/build123d-sandbox/

learning curve is steep, but the examples get you going in no time..

though not really CAD, favorite example: https://build123d.readthedocs.io/en/latest/examples_1.html#c...

shows the ability of this implementation of the open cascade kernel.. i havent found this kind of projection function too often in other cad programs, so this is really cool.. i remember trying to do similar with ptc creo and it was a pain..

latenode

2 hours ago

CAD has needed a proper code-first workflow for years. The existing options always felt like they were built for the GUI first and scripting was bolted on after.

wisemanwillhear

2 hours ago

In many ways this looks fun. I love the precise control and programming power of tools like this, but when I need something in real life, I never use them any more. The productivity of graphical tools is so much greater (as far as my brain works).

When I was younger I used POVray for a few small projects, but once I had access to graphical interfaces the difference in output quantity and quality was huge. I still keep tools like POVray installed, but all I ever do with them is tinker once in a while.

bityard

40 minutes ago

I remember running across POVray in the early 90's and not having a clue how to do anything more complex than a sphere with a light source.

Some artists have done some truly magical things with it: https://hof.povray.org

htgb

3 hours ago

Despite being aware of its existence, I stuck with OpenSCAD out of habit. Only last week did I read through the documentation, and feel strongly that I've been missing out… it seems to solve all of my gripes with OpenSCAD. I'm excited to try it out!

beering

2 hours ago

Mainly OpenSCAD is not a BRep modeling tool! It is not on the same level of power as CAD tools with a BRep kernel and this especially shows when you want to do a fillet over an arbitrary edge. Unfortunately these kernels are hard to make and integrate and I only know of two open-source BRep kernels out there: OpenCASCADE (used by FreeCAD and build123) and truck (not sure what the status of it is).

plumbees

3 hours ago

I've been wanting to get into OpenScad. Wondering what you've identified as an issue. I dabbled a little and I think I remember wishing it was more object oriented to make it a bit easier to make reusable adjustable pieces and I had found a python library that does openscad conversions; Wondering what gripes it solves for you.

greenavocado

20 minutes ago

B-rep (boundary representation) modelers (like build123d via OpenCascade) represent solids using faces, edges, topology geometry

OpenSCAD uses Constructive Solid Geometry (CSG) which represents objects as boolean combinations of primitives (union, difference, intersection). It does not maintain an explicit boundary/face structure internally

z3ugma

3 hours ago

I have been using this library for a few months alongside Gemini 3.1 Fast

It's really useful to get an iteration loop going with an LLM.

The OCCP viewer extension for VS Code helps make sure you can see and manipulate the resulting model

jpleger

2 hours ago

This is cool, seems like a next gen cadquery, which was really cool to see.

CarVac

3 hours ago

I like Build123d but I really want a hybrid mouse/code CAD built around it. I want to be able to click on entities and have them show up in the code editor instead of blindly trying to select edges.