Assembly branch

[kcleung]

I just noticed an assembly branch in the repository. What is it about and what new features are there?

[jdegenstein]

Assemblies and joints are undergoing an overhaul currently. In order to not put a drain on the limited resources here, I recommend joining the discord https://discord.com/invite/Bj9AQPsCfx where regular progress updates and discussions are happening about this assembly branch.

[gumyr]

There are several new features that will be introduced with Assemblies - see the Roadmap here: https://github.com/gumyr/build123d/wiki/Roadmap

I've recently discovered the STEP Application Protocol 242 which is a significant improvement of the current AP 214 that I'll be experimenting with. This will hopefully be a significant improvement but could potentially change the internal implementation of the Assembly class - more work to do.

Here is a quick summary generated by ChatGPT:

STEP AP242 Overview

STEP AP242 (Managed Model-Based 3D Engineering) is a modern STEP application protocol designed to handle:

• 3D geometry and assemblies (like AP203/AP214)
• Product and Manufacturing Information (PMI) such as tolerances, dimensions, and annotations
• Kinematic data, composite materials, and advanced metadata
• Lightweight visualization (triangulated meshes alongside precise geometry)

🧩 Key Features:

• Hierarchical assemblies with instancing (NEXT_ASSEMBLY_USAGE_OCCURRENCE)
• Precise B-Rep geometry and mesh representations (hybrid models)
• Semantic GD&T and PMI support (not just graphics)
• Support for product lifecycle management (PLM) integration
• Backward compatibility with AP203/AP214

🚀 Purpose:
AP242 aims to be a single, unified standard for 3D CAD data exchange, replacing older AP203 and AP214 protocols, and supporting model-based engineering workflows end-to-end.

[kcleung]

I see...... BTW how will the new assembly system work with partcad? We may wanna coordinate with developers from the partcad project

[kcleung]

@gumyr I am glad to see the updated roadmap where you propose the BuildAssembly system #231

https://github.com/gumyr/build123d/wiki/Roadmap

However, I also see a stale assembly branch last updated in July 2025. Is that assembly branch related to the BuildAssembly system mentioned in the current roadmap? Or is the code of the BuildAssembly system living somewhere else?

[gumyr]

Assembly is on the back burner for me now as I'm working on projection. That branch might provide a view towards what is planned but the implementation is likely to be significantly different.

[kcleung]

Thanks for your update @gumyr which branch should we look at if we wanna see the development of projection? This would be a good feature to go into 0.11. Looks like we need a few more point releases before we can call it 1.0.

[gumyr]

I haven't been pushing any of the projection work in the public repo but you can see some of my progress in the Discord.