A co-worker dropped off a small (key chain version) of this puzzle on my desk. I looked at it and thought with only 7 pieces, this should be a breeze. However, I soon found the puzzle very challenging due to the number of potential wrong solutions and the required order of operation during assembly. Anyway, his version was pretty fragile due to the size, so I thought I would scale it up. My version (3" cubed) was made from a scrap 2x4 and a 3/16" diameter dowel.

Here is video showing how it works.

Step 1: Tools/Materials

Tools:

Table, Hand or Band Saw
Drill Press
Drill Bits
Sander
Ruler
Pencil

Materials:

2x4 by 2' Long
Wood Dowel 3/16" Diameter x 18" Long
Glue

Step 2: Drawing

You will be building to this drawing. The parts are color coded for easy reference. Note that I kept the dimensions simple - each segment is 1" x 1" x 1" and the holes are centered at each segment.

I've also include STP and STL files in the last step in case you would like to 3D print the puzzle.

Step 3: Pins

Start by cutting the 3/16" dowel into six 3" Long pieces.

Step 4: Part 1

Cut the T - block as shown. There are a variety of ways to make the shape. I started off by cutting the 2x4 down to 1" x 3". This allowed me to do the main cuts with the table saw. For this part, I used a band saw after starting with a 3" x 3" x 1" block. Another option is to make or buy 1" cubes and glue the pieces together.

For the holes, note the difference in size. The hole that accepts the pin should be an interference fit (same size or slightly smaller than pin). The thru holes are larger to allow the puzzle to be assembled with ease. The larger size will also help if you are slightly off with your dimensions.

Step 5: Part 2

You will cut this same shape for Parts 2 - 5. This part is a pass through block. Note the hole sizes on the remainder of the parts are different.

Step 6: Part 3

Same shape as Part 2. Note the hole sizes. Center the dowel as shown.

Step 7: Part 4

Same shape as Part 2. Note the hole sizes. Add the the dowel as shown.

Step 8: Part 5

Same shape as Part 2. Note the hole sizes. Add the the dowel as shown.

Step 9: Part 6

Cut this part per the drawing. Add the dowel as shown.

Step 10: Sand and Paint/Stain

Try to fit the puzzle together. You might need to sand some of the sides to work out the fit. I added a walnut stain to finish the parts.

Step 11: Solution

This picture shows the solution in 7 steps. The last step is the insertion of the dowel.

Step 12: Complete Puzzle

Step 13: Final

Unfortunately, the CAD rendering looks much nicer than my version. I did the band saw cuts by hand and I missed centering up a few of the holes. It still works but not quite as polished as I would like. Anyway, it works and the average person should take about 15 to 30 minutes to solve the puzzle. Thanks for viewing.