To add a bit to what others are saying. Mesh mixer is sometimes a great tool for some of this. Source: 9 months ago

Ah right. If you can't get the source file, you could try smoothing them out in meshmixer. Source: 11 months ago

The quickest fix I know is to use the free meshmixer. Source: about 1 year ago

There are programs such as Meshmixer specifically intended to do that, others such as Blender which can do a good job (but beware of missing surfaces or inside-out triangles) and some CAD programs such as Fusion 360 which have the ability to convert meshes. Even Tinkercad can make some changes. It's always better to get a CAD file in a common interchange format such as a STP (STEP) file if you can, though. Source: over 1 year ago

Meshmixer seems to be no longer in developement, with their integration of similar features with fusion360 according to their site https://meshmixer.com/. Source: over 1 year ago

If computer graphics is of interest, BRL-CAD (https://brlcad.org) is very welcoming to new contributors and has lots of projects you could take on. Source: about 1 year ago

Mike Muuss[0] approves of this message. 0: https://brlcad.org/. - Source: Hacker News / about 1 year ago

Join an open source community that is welcoming to newcomers (e.g., BRL-CAD, Haiku OS, OSGeo, ..) and work on a little bit of code every day. It can be a simple feature, specific bug, or something new you want to achieve. Many open source groups are very welcoming to newcomers if you do the work and ask smart questions. Source: over 1 year ago

You could also try out free AutoCAD alternatives like libreCAD (2D), or brlCAD (2D&3D, I believe). Source: over 1 year ago

So, uh ... Learning curve. If you want anything and everything under the sun, go with BRL-CAD. It was designed for ballistics testing and simulation, but it can do pretty much anything. The learning curve for BRL-CAD is immense. Otherwise, I recommend OpenSCAD. Source: over 1 year ago