[JTxt]

You can use Blender for some CAD work... But it's not a solid modeler like solidworks/inventor. It doesn't have many of the precision and parametric tools.

Blender's internal representation of objects is vertices (defined with IEEE single precision floats) connected by lines, and faces --just the shell of the object, and no real curved surfaces (just more and more faceted to approximate curves, and smoothed normals to look curved.) It also does not have guaranteed precise measurements. Blender can do some parametric and Boolean operations and many of the same things, but sometimes it fails and the limitations get in the way.

Some have built CAD tools into Blender, but it's a hack on an artist's tool. For some types of CAD projects, it'll do great, particularly in some very creative directions, but I'd start with the other tools you mentioned.

I export Inventor models to Blender for better rendering and animation.

[naikrovek]

I think now you can define circles and extrusions parametrically. I'm sure I've seen videos of people adjusting circle radii and facet count and it adjusted the parameters and re-tesellated based on the new parameters. Visually you see the polygonal representation you asked for, but at least some things do seem to be parametric underneath if you define them in the proper way.

I also believe I read about parametric model definition being something they are working on more, since so many folks are asking for it. I do hope that comes to fruition. A free parametric modeler would be absolutely lovely.

[JTxt]

Yes, there's some parametric things you can do in Blender. You can have a beizier curve that you can later change the facet count on... and you can use a spin modifier on a shape, but you're not going to get a perfect tangent line off a perfect circle like you can in a proper CAD tool for example. and you can boolean with another object, are you're not able to add a perfect fillet at that intersection.

In Blender, with care and if you're clever, you can do many of the same things you can with a CAD program... good enough for many cases. But Blender is still more of an artist tool than an engineer tool. For serious uses you're going to run into the limits.

There are free cad parametric modelers. FreeCAD is one.

[naikrovek]

Yes, there is FreeCAD. It crashes constantly and is very difficult to use. ..it doesn't really count, in my mind; if it isn't usable, it may as well not exist at all.