Photo Block Puzzle Piece

A cube with inset faces, designed to make a Photo Block Puzzle, described at https://www.instructables.com/id/3D-Printed-Photo-Block-Puzzle/.
This design is also a handy example of how to create a hollow cube that has engraved figures or text on all 6 faces and requires no support.
Photo block puzzles are a fun way to give a friend a set of memorable photos. It’s like 6 simple jigsaw puzzles in one! Each block has one part of each of six photos. The challenge for your friend is to a) flip the blocks until all the squares from one photo are face-up, then b) rotate and re-order the blocks until the photo makes sense, then c) do it again for another of the six photos on the blocks.

BackHalfCube.stl is one half of one photo block. FrontHalfCube.stl is the other half. Bar.stl is the bar that holds the two halves together. Print 6 sets of blocks for a simple puzzle. Print without supports or brim.
Print the parts as they are oriented in the STL file: with the bar lying on its chamfered (beveled) face, and the two half cubes each making a little tent.
I successfully printed this design in PolyLite PLA on my Lulzbot Mini printer, slicing it using Cura Lulzbot Edition set to the Lulzbot Mini Standard Resolution.
Note that each half of the cube has a pair of slots in it. These slots will hold the bar that will keep the two halves in position while the glue sets. Using E6000 Craft Glue – or whatever plastic glue you prefer – put a blob of glue in each of the four slots (two per half-cube). Also run a bead of glue along the two short edges of one of the half cube pieces. Place the bar in the slots in one of the half cubes, then press the other half-cube's slots into the bar to form the full cube. Make sure the cube halves are aligned, then hold the halves together until the glue sets (about 30 seconds for E6000). Once the glue has dried, if desired use a hobby knife to remove any imperfections or extra glue from the outside of the cube.
See https://www.instructables.com/id/3D-Printed-Photo-Block-Puzzle/ for how to create a photo block puzzle from 6 of these cubes and 6 photo prints.
BlockPuzzleCube.FCStd is the FreeCAD design file. I started the design by creating the hollow cube, then created an indented square on each face of the cube. To make the cube printable without supports, I split the cube diagonally using Boolean operations and a cutter Body, to create two tent-shaped halves. I then added a slot cutout and a bar to fit into the slots. I created only a little clearance (about 0.25 mm) so the bar fits tightly to hold the halves in place while gluing. I chose the size of 53 mm to nicely divide a 4 inch by 6 inch photo into 6 nearly-equal pieces 51 mm square, with a little room to allow for errors in marking and cutting the photos into squares.