How does CAD modelling work in Blender? I thought solid geometry manipulation like in CAD software was fundamentally different to what Blender does (surfaces only)?
There's https://www.cadsketcher.com/ addon for Blender. Blender isn't really a CAD program, but apparently it's got enough 3D functionality that it's possible to do CAD in it. Would need to hear from someone more familiar with CAD than I to know whether it's really viable yet or not. Blender's excellent for everything I've personally needed to do in 3D thus far though. (Mostly models / animations for use in game engines.)
It is a stretch to call Blender a CAD. What I think distinguishes parametric CADs is that in Blender you edit the body while in CAD you edit a set of operations that produce the body. This sequence is then processed by geometric modelling kernel to produce the end result. Editing and rendering is the easier part of it.
Sketcher mentioned is probably letting you create dimension accurate objects by hand, but it is far from being a proper CAD.
A 5s check of the documentation (so I may be way off), looks like Sketcher co-opts blender's UI to make it a front end to a CAD app (SolveSpace). So it does get you operations modeled to geometry like a real CAD app.
Blender doesn't support STEP file import or export, so it is not a viable CAD program. The add-on is probably great for creating dimensioned parts for use in animations and other things Blender does. But there is no interoperability with manufacturing or simulation tools.
Thanks for all the responses. As I said, I'm not a "CAD guy", so I didn't really know for sure, but now at least (thanks to y'all folks) I have a somewhat better understanding where "the line" between Blender 3D (and similar programs like Maya, Lightwave 3D, etc) and CAD actually lies. ;)
CAD modeling in Blender is only possible with geometry nodes.
I did some projects using geometry nodes. It is a nice step towards CAD modeling because it is fully parametric.
CAD models are mathematical models and thus infinit accurate. Solid models are not. But sometimes they are good enough. I create a lot of models in Blender for 3D printing.
In the BlenderBIM Add-on, CAD modeling works by providing a dedicated modeling interface that interacts with the IFC data model. IFC is an ISO standard that describes geometry, data, objects, processes, and relationships, for the built environment (i.e. BIM). IFC's geometry is based on STEP, so modeling in IFC has similarities to modeling in STEP. You can have swept solid extrusions, revolutions, true arcs and circles, but also some things that don't exist in STEP but are specific to the built environment, like the parameters for an I-shaped beam.
So like other Blender add-ons that do this already (e.g. CAD Sketcher) the BlenderBIM Add-on bypasses Blender for most geometric operations. You define using the dedicated modeling interface, the IFC data model is updated, then the triangles are visualised by Blender, but the under-the-hood CAD definition is there.
The geometry processing layer is done by IfcOpenShell, which is a layer on top of OpenCASCADE (but in the future, may make more use of CGAL or its own custom geometry processing code).
That said modeling buildings are typically simpler than manufacturing CAD modeling. Buildings have forgiving construction tolerances, and are often assemblages of off-the-shelf products where it is not necessary to redefine the exact product shapes. (i.e. place a packer here, place a sprinkler there, whether the sprinkler looks like a sprinkler or is geometrically just a cube in my model makes little difference to construction or maintenance operations).
I'm not currently aware of any integration, but since it is based on OpenCASCADE, there may be certain shapes that "just work" with IFC. This is similar to how FreeCAD uses IfcOpenShell to directly serialise some FreeCAD shapes into IFC geometry.
In my experience, it isn't really very good at it. I've moved to OpenSCAD for cad work, and am very happy with its design philosophy (if not its user experience)
