If you want to create 3d models which can be 3d printed, then you need to use a 3d CAD program. I use FreeCAD, which by the name, you can tell is free. It's quite capable. I have used it to create various designs including a fixture plate for my rotary table, a set true back plate for my lathe, and all the parts I needed to make an electronic lead screw system for my lathe. FreeCAD is available on Windows, Mac, and Linux. It can even run on a Raspberry Pi - I tried it.
As we speak, I am 3d printing an enclosure for my ELS system on my 3d printer. There are no fees, or yearly maintenance charges whatsoever to use FreeCAD. There is an active forum that answers questions of both new and seasoned users. I cannot speak to multi-axis machine control, as I have not dabbled there.
The level of effort to learn 3d CAD is considerable. However, once learned, it is quite empowering. I think it was worth the time learning. CAD is not a substitute for common sense, but it sure helps one see the spatial relationships amongst various elements.