Hi,
I miss this very important thread.
For me as general mechanic in CADs:
- Assembly as mechanical assembly is described in the first post of this thread (jpg87).
I prefer to separate components from assemblies in separate files. Do not mix assembly and components in one file. It means, assembly is:
a) Zero or more links to part files with Parts (components), each part file containing one Part.
b) Zero or more links to part files with another assemblies.
c) Positioning of the components and assemblies.
c.+) absolute positioning.
c.++) relative positioning based on constraints/joints and dimensions.
d) Possibility of different fixed configurations (doors open / doors closed).
e) Possibility of (semi) automatic BOM.
f) For me is less important deformable parts (springs, ropes, …), but it could be helpful sometimes.
g) For me is totally unimportant kinematics and dynamics simulations and visualisations. But apparently for many people (not only) here it is crucial part of assemblies.
h) Assembly cuts and assembly adds are usually on the black list of modelling technics - these technics broke the concept and usually have side effects on drawings and other modules/parts and complicates all on the background.
i) Harness (wirings, pipes, …) should not create geometry in the assembly level, but in the component level. Do not break the concept. Breaking of the concept has usually side effects similar as assembly cuts. It should support link of necessary geometry from assembly to part file (component) with harness.
\ - Assemblies in CAD is a way how to cooperate on bigger project with more people and more modules.
a) Drawing problem. I want to see my drawing files with drawing numbers and names independently to source 3D geometry part files. It means for me drawing file is assembly with one component (or one subassembly) I’m making drawing of. If I want to order component, I have to give PDF/paper drawing of the component with tech. specifications to my manufacturer. And if he needs to discus something, he has the drawing number… At the end when project became to manufacturing phase, everything is about drawing numbers and BOMs of drawings + fasteners + all others…
b) Technological assemblies. Sometimes design is not possible to manufacture in one simple step. Sometimes You need to make more complex set of technological models. Examples:
b.+) casting. You have final component after manufacturing. You need casting semiproduct prior to machining and it is totally different model. Then You need split it to molding models…
b.++) Welding of bigger structure. Your design is functional final geometry. For manufacturing you need to make unmachined after-welding model. Then You need to separate it to basic welding components or more welding subassemblies + particular machining… At the end You finish with simple basic semiproducts You can order from steel suppliers…
c) FEM problem. Designer makes 3D geometry. FEM specialist need to make his own things with the data. He has 2 options:
c.+) Make copy of the part file(s) and work directly on it. But this is non-associative copy. If the designer changes something, he will not know it.
c.++) Make its own FEM assembly where the design is just component or subassembly. Now he has live data…
d) CNC (miling machines or 3D print…) the same.
e) …
For me and industry (at least segment of industry I’m part of) assembly is much more than just mechanical assembly.
(I do not do this complex things in FreeCAD. FreeCAD is just my hobby for small projects - aircraft models and other my hobbies. But If You want to make good CAD with assembly, it could be good to take into account this ideas and experiences.)
Sorry for too long post.