So, I have two pieces of 3D CAD software I use the most for my models when I design something for 3D printing. First and foremost is FreeCAD: https://www.freecadweb.org/ Second is Design Spark Mechanical: https://www.rs-online.com/designspark/mechanical-software Both do a wonderful job of creating 3D parametric models that are air tight when you export them as STL files. FreeCAD has a higher learning curve and requires a considerable amount of patience to adapt your Inventor/Solidworks experience to the interface it provides. Without any 3D CAD experience, you actually might start off easier because you learn the FreeCAD model design philosophy from the ground up without other philosophies (and keyboard shortcuts that don't work in FreeCAD) inserting themselves into your work flow! YouTube and Wiki reading are a must with this one. Personally, I think the effort is well worth it with the numbers of models I've created and been able to modify again and again to create further variations. If you know what a design feature tree is, FreeCAD has one, and it allows you go in and edit each feature you add to a model. I've yet to play with assemblies, but it has that capability. 2D drawings can be created using some of the Workbenches, but I rarely use those (especially since I have AutoCAD). I have not found any way to import a DXF into the sketcher however, so some of the workflow I use in sheet metal design won't translate well into FreeCAD from AutoCAD like it can for AutoCAD to Solidworks/Inventor. I'm sure that it is merely a matter of time, or a matter of finding the right command in the correct Workbench (wiki/YouTube time). Design Spark Mechanical is a neat program created by Spaceclaim (who make analysis and simulation software for engineers) for Allied Electronics. It is geared for 3D printing enclosures for electronic equipment (and is linked to the Allied Electronics catalog, beneficial for sales obviously, and full of useful parts for industrial PLC designers...). Take the ease of Sketchup, and add the parametric controls and precision dimensions you can achieve with Solidworks/Inventor; and you have a great piece of 3D modeling software that exports flawless STL files for 3D printing! Obviously, the free version is limited compared to the paid version (no thread creation tool for example, along with no 2D drawings that can modify the 3D parts when edited), however for the hobbyist this provides a much more user friendly tool for creating 3D printable bits and pieces. So far, all my parts have been miniature bases. I haven't ventured into using either to create vehicles or buildings, yet. I do enough of that at work (well, utility poles at any rate).