This guide shows you the basics of converting an STL file to a STEP file. STL files are a 3D mesh format mostly used by 3D printers, but in the world of engineering CAD and CAM, most software requires solid models. The most universal solid model format is STEP (.stp, .step). Ideally you'd begin with a solid model and avoid STLs entirely, but maybe you found the perfect object on Thingiverse or you used a 3D scanner, and there’s no reasonable way to begin with a solid model. Or maybe you're already doing solid modeling, but you need to incorporate an STL model into it. This guide shows you a file conversion process that has worked well for me.
Disclaimer: STL files span a wide range. Some of them are low-complexity, watertight, and can be easily converted. Others are extremely complex, full of holes and self-intersections, and will cause the conversion application to crash. If your STL file is of the second type, you won't be able to convert it. That being said, if you have no other option, it’s definitely worth a shot!
STEP 1: DOWNLOAD A CONVERSION TOOL
Our conversion tool of choice is FreeCAD because it’s free, relatively simple to use, and does a good job of converting STL files to usable solid models. Download it here.
STEP 2: IMPORT YOUR STL FILE
Create a new file (File menu > New).
Import your STL file (File menu > Import > select your STL file).
From the dropdown menu in the top toolbar, choose Mesh design (see screenshot).