Wooden Puzzle Box

The first time I saw a puzzle box I was intrigued at the precision and craftsmanship involved. Something about the beauty of the wood and the challenge of the opening mechanism really stuck in my mind. Having built a handful of wooden boxes before, I decided it was time to make my own!

The mechanism to open this box is quite simple if you know it and thought provoking if you don't. Tip the box left or right and you'll hear pins sliding internally, but the lid won't come off. Give it a quick spin or two and voila, the box opens! It's hardly magic that keeps this box shut, rather a set of interlocking nails and slots. When spun centrifugal force pushes the nails out of their respective slots against the internal walls of the box allowing the lid to be removed. Think about swinging a bucket of water in a circle and you'll understand what's going on.

The box is constructed from two contrasting woods, walnut for the sides and maple for the lid/bottom. I started with rough lumber and milled it to size, however I designed the box to use common materials sizes. Other than the nails used for the locking mechanism, the box is held together with common wood glue. I used a specific set of tools and techniques to build this box, but there are many alternate methods, look for alternate recommendations and swap as you see fit.

Tools

• Table saw
  
  • 90 degree cross cut sled (or miter saw)
  • 45 degree cross cut sled (or miter saw)
• Hand saw (or bandsaw)
• Drill press
• Strap clamps
• A bunch more clamps!

Materials

• Wood Glue (TiteBond II)
• 21 in x 2.5 in x 0.5 in board (for primary box wood, I used walnut)
• 12 in x 5 in x 0.75 in board (for bottom, lid, mechanism, I used maple)
• 2 in nail (6 total)

The side panels will be made from the 21" board. Each of the four side panels has a slot for the bottom panel. To make this slot we will utilize a table saw with the blade height set to 1/4" and the table saw fence set at 2 1/8". The 1/4" height ensures the blade only cuts half way through the board, leaving one piece with a groove instead of two pieces. Given that our box height is 2 1/2", setting the fence to 2 1/8", allows for a 1/4" offset off the bottom of the box and an 1/8" groove. Note that some blades might not be exactly 1/8" thick, keep this in mind when making the bottom panel, adjust thickness as necessary.

Using a miter saw or a cross cut sled, cut four 5" panels from the 21" inch board with the groove from the previous step. Clamping a stop block at the desired distance will help ensure each side is exactly the same size. There will be approximately 1/2" of material left over, as each of the four cuts will remove a blade's width of material (1/8"). Adding an additional inch to the initial material list ensures we have enough material for all four sides.

Cut two 45 degree miters on each side panel, keeping in mind that the groove for the bottom panel is on the inside of the box. The outer face should remain 5", while the inner face will be 4". These cuts can be performed using a compound miter saw set to 45 degrees or using a 45 degree cross cut sled on the table saw. Pay close attention to alignment, the more precise these cuts are, the less noticeable the corner seams will be.

The bottom panel will have a thickness slightly less than the width of the table saw blade. We will ultimately need a piece measuring 4 3/8" x 4 3/8" x ~1/8". The 1/8" thick bottom panel will be resawn from the 12 in x 5 in x 3.4" board. A band saw is the preferred method of making this cut, however in the absence of one a table saw can be used as well. For more information refer to this great video by Marc Spagnuolo (aka the Wood Whisperer). A thin kerf handsaw is useful if multiple passes are needed, leaving a small bit of material keeps the thin off cut from moving around.

Using a miter saw or cross cut sled, cut the thin bottom panel to 4 3/8" x 4 3/8". The panel is slightly undersized relative to the dimensions of the slot to allow for some movement during glue up.

Align the four side pieces such that the bottom slots line up on all pieces. A long strip of painters tape is useful to keep the pieces aligned during assembly. Add wood glue to the mitered edges and into the cut slot.

Insert the bottom panel into the grooved slots of the side panels one at at time until the box is closed. A small amount of pressure might be necessary to ensure the bottom panel is evenly seated across all four sides.

Clamp the edges and allow the glue to dry overnight. Traditional bar clamps can be used, however strap clamps are significantly easier to ensure even pressure on all corners.

From the same material as the top and bottom panel (in my case maple), cut a 4" x 1.875" x 0.5" piece to serve as the locking mechanism. This piece will ultimately be cut in half to create two piece, but to ensure good alignment in the next step, we will use one solid piece. Mark six equally spaced points along one of the 4" x 0.5" faces, which will correspond to nail hole for the locking mechanism. I used a drafting compass to precisely determine the hole spacing.

Using a drill press, drill holes all the way through locking mechanism at the six previously marked locations. I used a 1/8" drill bit which was slightly larger than the diameter of my nails, allowing for some tolerance. It is important to size these holes properly to your own nails to ensure proper alignment later on.

Using a table saw cross cut sled (or equivalent) cut the drilled locking mechanism in half to create two 4" x 0.875" x 0.5" pieces. Mark the orientation on each piece for reference in later steps.

Using a pencil mark a rectangle on one of the inner side walls of the box. The top of the rectangle measures 0.75" from the top of the box, the bottom measures 1.25" from the top of the box. One side of the rectangle measures 0.875" from the perpendicular face of the box and the remaining side measures approximately 1.75" from the perpendicular face. Mark an identical rectangle on the opposite side wall as the first. These rectangles mark where the internal locking mechanism will be secured to the side panels.

Take one half of the drilled locking mechanism and insert 2" nails into every other drilled slot. Add a dap of glue to the previously marked rectangles on two opposing side walls and carefully align the internal locking mechanism. Note the orientation of the nail heads, they should slide without falling out.

Using a hand saw (or bandsaw) cut two pieces to serve as lid supports measuring 2.25" x 0.5" x 0.125".

Glue the two lid supports to the inside faces of the box ensuring that the tops are flush with the locking mechanism and not obstructing the sliding nails.

From the same wood as the bottom panel, cut a 4" x 4" x 0.5" piece to function as a lid. If the thickness isn't 0.5", either plane/sand to 0.5" or account for the extra thickness when aligning the locking mechanisms in later steps.

Glue the second half of the locking mechanism to the inside face of the lid approximately 2.125" from one edge and 1" from the opposite edge. Using a hand saw cut 0.125" off the narrower faces to allow the lid to pass by the internal lid supports. Using a handsaw (or bandsaw) cut a 3.5" x 0.125" x 0.125" strip of (lid) material. Add nails to every other drilled hole (verify that they aren't the same holes as the internal locking mechanism). Glue this strip in place to serve as a stop for the nail heads.

Cut a 1" x 0.5" x 0.5" piece of wood and glue to the center of the lid on the opposite face from locking mechanism. I used walnut to contrast the maple lid.

Challenge your friends to discover the secret, store your valuables, bask in the glory of a job well done.