Simple 6-piece burr - For Starters!
thingiverse
This is probably the most accessible classical 6-piece burr puzzle out there. It's a fantastic one for beginners to learn how the solution looks like. After mastering this one, consider moving on to this set: https://www.thingiverse.com/thing:4041348. This collection has puzzles that increase in difficulty progressively. This STL was created using Enso (http://www.jeremyrayner.com/puzzles/enso/) from the attached .xmpuzzle file. Enso can output OpenSCAD files, which reference Aaron Siegel's Puzzlecad library (https://www.thingiverse.com/thing:3198014) to render the final STL. You don't need the .xmpuzzle file at all. It's a file that can be loaded by Burr Tools (http://burrtools.sourceforge.net/) for exploring and solving this puzzle. I highly recommend printing on a raft.
With this file you will be able to print Simple 6-piece burr - For Starters! with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Simple 6-piece burr - For Starters!.