5L Box Packing Puzzle

The 5L Box is a highly acclaimed packing puzzle designed by Hajime Katsumoto. It gained significant recognition in the puzzle community by winning the Jury 1st Prize at the 2018 IPP38 (International Puzzle Party) Design Competition.

The objective is to pack five identical L-shaped pieces into a wooden box and close the lid.

Even though few may build this, I designed it as a "no compromise" version of Katsumoto's puzzle that has excellent operation and is visually appealing. It is well worth building and one of my favourite puzzles.

There were a few iterations of this design. Its goals were:

1. To provide a window into the chamber while restricting access. Seeing into the box is necessary for the solution.

2. To add a mechanism to keep the door closed. I originally used a friction fit, but it was difficult to get tolerances just right; and it would not be reproducible across various printers. The best solution was to use magnets. I used 3mx1.5mm round. However, this feature is optional and still works fine without magnets, if you do not have them.

3. Provide a great aesthetic look and feel for the puzzle.

Printing

The box can be printed at 0.3mm layer height for speed, or 0.2mm layer for quality. (The 0.3mm height still looks great in most filaments). I use a 3mm drill bit to clean out the magnet holes a bit. If you don't have a 3mm drill bit, print the box at 0.2mm layer height to get a bit more accuracy. I used 4 perimeters, 3 top/bottom walls. 15% Rect infill. The box did not require any supports. The bridges across the side cutouts printed fine.

For the handle, I used 0.2mm layer height and 6 perimeters to make the part solid.

The handle will require support and I used painted-on supports as shown in the picture (0.2mm Z distance, snug). If you notice drooping on the insert parts, trim with a knife.

For the sliding door, I used 0.3mm layer, 3 perimeters with 3 top/bottom layers and 30% infill.

For the pieces, I used 0.3mm layer, 3 perimeters and 50% infill as I wanted these somewhat solid.

I used color changes by layer height for:

1. The floor.. I like a white floor to contrast the walls

2. The text on the sliding door

Assembly

All printers are slightly different and you may find that you need to sand/file some edges to get a perfect fit.

For the window I used a $1 plastic cover (school supplies) that I found in my local "Dollar Store", in Canada. It was a pliable plastic (not brittle) and cut easily with scissors. I could almost cut through it with an "Xacto" knife. It was quite clear and 0.56mm in thickness. Tinted plastic is fine as long as you can still easily see the pieces through it. I provide a square of the exact size so you can place the square over the plastic and cut. The window should be 48x46mm (you have 0.5mm tolerance). You may find you need to trim with scissors for a final fit. The window should be 1mm below the flat face on which the door slides. Get the window the correct size before applying any glue. Put glue on the inside pillars then drop the plastic into the groove. While you have access to the top 1-2mm of the plastic, put some glue across its top then do a final push down into the groove. I had a small clamp to hold the plastic to the wall as it dries.

Note: One user used a Scotch Thermal Laminating Pouch that was 5mil thick.

If anyone needs a different thickness of groove cut into their box, let me know and I'll add a custom size. Do not exceed 1mm because the sliding door may not be supported properly.

Optional: The rare earth magnets I used were 3mm x 1.5mm in size. You can order these cheaply from AliExpress. Note that the exact thickness can be difficult to obtain from some vendors. If you order 3mmx2, you usually get 1.6mm thick and these are fine. The holes in the box are 1.9mm deep.

Glue the handle into the door. I put a magnet on the end of a 4mm or larger rod (I use a larger hex Allen key). Add glue to the magnet hole and press the magnet into the hole. The large rod should stop at the wall face and prevent the magnet from recessing too far.

Once the glue has set, I add 1 more magnets on top of the glued one on the door(don't glue it). Add a small drop of glue into the box magnet hole. You can push the door into the box and that extra magnets may magically push and stay in its hole in the box. If not, you'll need to insert manually with a rod (double check you have the polarity correct!). Remove the door and allow the glue to set and then test the door/box operation.

To assemble the door/lid, you first place glue on the outside lip of the lid as shown in the picture. Do NOT get glue on the top surface or you may glue your door to the lid and it will not move. Next put the door so its bottom cube is inside the box area. Find the front of the lid, and orient it correctly so it is on top of the door and being glued to the box edges. I used 2 small clamps at the back and front edges. The door must move relatively freely and should be mostly open.After 5 minutes of gluing, check the door still moves freely.