3d design Software

I like SketchUp, it was the first intuitive CAD I encountered, nowadays you might also look at Fusion360 (I think it's free if you make your work public)

Fusion 360 is free if not for commercial purposes. There is no requirement to make your work public, nor can I see any way you can do so unless you supply the files or specifically upload it to the autodesk fusion 360 project gallery.

Sketchuo, Easy peasy. Very comprehensive

Thanks a lot guys. I'll give them a try.

A large aerospace company developed and used software for designing wiring for large 3D very expensive aerospace objects. It would have been good if it hadn't assumed that the cable thickness was zero instead of several centimetres or that the object was two dimensional.

Sketchup works for me - I use if for most projects in one way or another. You can go for either a "here is what it will look like when finished" model, or go right down to "here is how every joint fits together". I often go for the former as an aid to visualisation and design. (I really ought to go for the latter more often since it can really pay off in reduce build time and errors!)

So some "big picture" and getting the dimensions in the right ballpark designs:

Which became

Slightly more carefully modelled:

This one I modelled down to some of the joinery:

(which you can't really see unless you can look around the model!)

I use RhinoCAD but its aboiut £700

There is also DraftSight. The 2D version is free, and if you like that you could pay for the 3D one. But for most woodwork, 2D should be fine.

There is, and people I know who are used to AutoCAD say it's great; I never put AutoCAD in the intuitive category but it's ages since I tried it.

I got used to a decent CAD prog (which is still supported/being developed) on this ancient Acorn machine and DraftSight is fairly similar on the PC. (although not as good as the one I know well ;-)) And can share files between them. But they are a steep learning curve.