Nail Puzzle Box

This is a remake of the excellent puzzle box produced by Fathomlis shown here. My version has different dimensions and building techniques and is also fully documented in CAD format. In addition, I included some optional 3D parts which could speed up the build and provide better performance.

The goal is to open the box. There isn't any secret panels or buttons to push. Watching the video is the easiest way to see how it works.

Tools

• Table or Miter saw
• Drill press
• Drill bits
• Wood clamps
• Sander
• Screwdriver

Materials

• 3.5" x 1/2" x 48" long hobby wood (poplar)
• Nails, 2.4" Long x .114" diameter (x6)
• Knob
• Screw, #6 x 1/2" Long (x2)
• Screw #12 x 1" Long (x1)

• Wood GluePaint or Stain

You will be building to this drawing. All parts are color coded for easy reference.

You might want to refer back to the section cuts while you are building the project.

To reduce the amount of cuts, I used the purchased 3.5" width for the box parts. The long sides are 7" x 3.5". The short sides are 3.5" x 3.5". Make 2 of each. You might want to do a light sanding at this point to the inner sides of the box since they will be hard to reach once it is put together.

Cut both of these to the same size (6" x 3.5"). The top size will be reduced in a later step. Also, hold off on drilling the knob hole until later.

These are used to support the lid and nail blocks. Using the same 1/2" thick wood, cut strips as shown. I used a table saw for these cuts. You will need two of the 6" long strips and one of each for the other sizes. Note the 3.44" strip is for the top. You might want to leave it 3.5" for now and shave it later when fitting the top.

Attach the 6" strips to the long side as shown. Fastening options include nails, screws and/or glue. I only used glue and applied pressure with four clamps. Repeat for other long side.

Attach the sides to the bottom as shown. Again, I just used glue and pressure for the connections.

Apply the 3.5" side strip. Again, glued in place.

At this point, do a fit check on the lid. Don't push it on. If so, you might not be able to get it off. Shave the sides enough so that it easily fits in the box. My average gap worked out to 1/32 of an inch. This is iterative process so take your time. Before you push the lid all the way into the box, I suggest adding the knob. To find the center for the hole, draw lines from corner-to-corner. I used a knob that was supplied with a #12 screw. Make sure to countersink or counterbore this hole so it doesn't interfere with the nails. Add the knob as shown. Do another fit check on the top. Tip - using sand paper allows for finer adjustments.

This is the toughest part of the project. It is also nail dependent. The dimensions shown are for nails I had available in my shop (see step 2). If you have a different size, adjust the holes according. As I mentioned in the intro, mixing 3D printing with wood working is an option. I've designed and included STEP and STL files for printable versions of these parts. The countersink mounting holes also allow you to adjust the placement in the box.

For the woodworkers, I started with a large piece of hardwood scrap. The thickness was 1/8" thicker than twice what was required for the parts. This worked out perfectly since I wanted to drill the holes once and the cut the piece in half. The extra 1/8" accounted for the blade width. I drilled the holes as shown - see first picture. You could also add the tapered (countersinks) at this point as well - slow down and think while doing that step. Next, cut the block to 1/2" wide by 3.5" long. Now cut the block along the centerline to make two pieces. Make sure to mark the pieces so you can reinstall them with matching holes.

Drill and countersink holes on the ends as shown. Note that these holes are for # 6 flat head screws.

You will need to place 3 nails in the block. Pay attention to the orientation - nails go in non countersunk holes. If you used the same size nails as instructed, position the nail block in the box as shown. You will need to do the positioning calculations if you try a different length nail. If you can't figure it out, leave a comment and I can help you work it out. Use the # 6 flathead screws for the attachment (don't glue at this point).

Add the nails and block as shown. Since you have a lot of surface area, the screws are optional on this piece. However, if the design doesn't work correctly, having the ability to remove the nail blocks is pretty nice. Again, if you 3D printed them, you could easily adjust the nail hole size and reprint them.

Sand as desired. I used a dark cherry stain and two coats of spray polyurethane.

In order to install the top, position the nails in the outward position on both the box and the top. Next move the box back and fourth. This motion locks the box.

The trick to opening the box is centrifugal force. To open the box, the key is to spin the box as shown in the video.

I guess these look better than the cartoon images shown earlier. :)

All images show the nails in a random pattern. The second two pictures show the top taken off but the top nail block included.

I'm pretty happy with how it turned out. Thanks for viewing.

I made a smaller, 3D printable version. This one is much easier to make :).

https://www.instructables.com/id/Puzzle-Box-3D-Pri...