I’ve tried working with sketchup and I couldn’t work with any program that doesn’t allow you to go back and change history. I’m talking about a history tree not past versions Programs that don’t have history in my opinion are more for artwork. Also being able to set dimensions is important.
That narrows it down to popular programs like freecad, fusion, onshape, Alibre and others. Again none are specifically designed for 3d modeling.
first off I have your feelings about subscriptions and try to avoid them. One issue i have is a lack of internet. If it wants to talk home, I have problems. I have found that Fusion (the free version) wants to talk more than i am comfortable with. TinkerCAD and FreeCAD have both been mentioned. A lot of what you want to do with the programs depends on how you learn and will they work for you. I will throw into the ring OpenSCAD. It works like a programming language in that you code what and where you want it. It works great. It is free with a whole community of support behind it and tutorials are available and there are books to help also. it also allows for customization of designs with varibles. If you check out Thingaverse and Printables you will see designs that take advantage of this feature.
It is easy enough to learn and is very good with mechanical designs. If you are patient you can design just about anything (and yes some organic designs are possible)
I have a question. which programs that are mentioned above allows you to import a STL file and alter it? I am not talking about adding to the STL but a program that converts the STL to a solid, so that you can work on it?
I know SketchUp can and I think I’ve seen people using Fusion do it.
Pretty sure they all can convert a mesh to a solid to some degree. Editing the produced solid is going to make for a not so fun experience though. The question probably should be, which software makes that editing process easier. I have no answer for that 
Fusion can convert a simple mesh, but it is a painful manual process in the free version. YouTube has a few tutorials that show the process and also a couple other methods in the paid versions of Fusion. Being cheap and lazy, I don’t attempt STL conversions any more - it’s usually quicker and easier to make my own design from scratch.
I also would rather build something vs modifying it.
I had the need to print a timing belt pulley. Something like this and gears are a pain to design. McMaster-Carr has models that you can download. I can’t download STL but I can download step files.
So I imported the model into Alibre and want to modify it… you can always add, subtract or scale shapes of the solid but you can’t a change a feature. What’s cool is this program has the ability to pass a plane thru the solid and generate a sketch outline. So I was able to completely rebuild the pulley from the projected sketch of that solid. I used their tooth outline as a basis for a completely new timing belt pulley. Based on this I’m not sure I would need to modify a mesh file.
The reason why I asked is, and I know this is strange, but Siemens NX12 can’t convert STL’s to solids, so that you can then manipulate it, but SketchUp can.
Also Siemens NX12 doesn’t have a gear function which allows you to input gear data and then draw it for you, but again SketchUp can with a free extension.
All but the most complex gears are 2D. My issue with DXF is the excessive amount of points involved.
When it comes to which CAD is it’s all about what you can learn and what works for you. What works for you is very tied to what you plan to design. So general discussions don’t help. Sign up on a sketchup or whatever forum and ask them :).
Appreciate all the replies, recommendations and links - plenty to look at and think about so many thanks for that.
I have no intention of selling anything as this would purely be for personal use, sharing and of course making things for friends so unlikely to be hit by any sort of commercial license although never say never I suppose.
Thanks & kind regards,
-=Glyn=-
-=Glyn=-
I have no problem with SketchUp. I am a member of their forum. I also have a payed licence for it. It’s a great package that can do a lot.
I was just curious about what other 3d drawing packages could do.
For simplicity but enough power for me as a first time user, MatterControl from MatterHackers (dot) com did what I needed in the free version. They also have MatterCad, but I haven’t tried it. MatterControl will also slice but I didn’t use it for that. It loads and exports .STL files and let’s you add other 3D shapes and add and subtract them to create the final model. (Maybe that’s how other CAD programs work, but I don’t know.) I wanted to lengthen the pin on top of a base that plugs into a blocking board. I was able to combine the existing model with a longer cylinder and a half-sphere to get what I wanted. I hope that helps.