Dowel Lock Puzzle

This is an advanced version of the puzzle I posted a few weeks ago. I incorporated a few lessons learned from that project and also came up with a way to reduce the required accuracy. The solution is similar but I've added in complexity and a little decoy to throw the puzzler off the scent :).

This video shows how it works:

** I will give Instructables premium membership to the first person that builds a version similar to my design. I encourage changes and/or improvements that I might have missed. You must post a picture in the "I Made It" part of this Instructable **

Tools:

• Table Saw
• Drill Press
• 3/8" Forstner Bit
• 1 1/4" Forstner Bit
• Router and Chamfer Bit (optional)
• Ruler
• Pencil
• Sander

Material:

• Wood Block: 3" x 3" x 3"
• Dowel: 1 1/4" Diameter x 3" Long
• Dowel: 3/8" Diameter x 6" Long
• Glue/Epoxy
• Magnet: 5mm Diameter x 2mm Thick (x4)
• Steel Ball: 3/8" Diameter (x2)

You will be building to this drawing. The parts are color coded for easy reference. As always, measure your actual parts during the build and adjust the dimensions accordingly.

You will need a 3" cube of wood for the puzzle. I didn't have anything that thick so I laminated some scrap pieces together. For mine, the ends are maple and the center is mahogany. Two layers of 1/4" wenge were used to fill up the stack. After lamination, I cut the piece down to the 3" cube.

You will need to cut a 1.25" Diameter hole through the block. I used a Forstner bit (not the one shown) for this task. Unfortunately, my weak Harbor Freight drill press didn't have the power to push through 3" of hardwood. Thankfully, I have a buddy with a high end machine that could drill the hole without any problems.

Slide the 1.25" dowel through the hole and mark off the length. Cut to size.

Lining up the two "B" holes in the puzzle is key for proper functionality. Refer to the drawing and proceed with the following steps:

1. Measure and mark the hole locations on the Block per the drawing, Note that the four sides are the same.
2. Place Dowel into hole.
3. Mark the side of the Block and Dowel with identifier marks so you can reorient it later (see pictures).
4. Hopefully, the Dowel fits tightly into the block. If not, secure it on both sides with tape to prevent spinning.
5. Drill the two "B" holes through the Block and slightly (enough to mark center) into the Dowel.
6. Remove Dowel
7. Test your holes by dropping a ball through the hole. It should drop to the center without any binding.

The hole locations in the Dowel should be clearly marked from the previous step. Use a 3/8" Forstner bit to drill a hole to the .188" depth shown on the drawing. I suggest using the steel ball as a gauge at this point. Drill short then do a fit check. Drill deeper until the ball sits exactly half way in the hole.

Next, use a 3/16" drill bit and drill the magnet hole per the drawing. Note that magnet diameter is 5mm which is approximately 0.197 inches. Since I wanted a press fit, the holes 3/16" (.188") worked perfectly. Note that the depth shown on the drawing is deeper than 2mm (.079"). This gives you options to push the magnet deeper into the hole to reduce the force required for separation. I strongly suggest you practice this hole/magnet combination on a scrap piece of wood before locking down your final dimensions.

Fit check. Place Dowel back into the Block. Use your marks from the last step to align the Dowel holes to the Block holes. Drop a ball into one of the holes. The Dowel should now be locked. Flip 180 degrees to remove the ball. Repeat process on other side.

At this part of the build, I only had pencil marking on the Dowel and Block to help with alignment. These markings were slowly disappearing with handling so I needed something more permanent. I'm sure there are nicer ways to mark it but I settled on a swipe across my table saw to create the groove. I placed the Dowel in the Block and ran a single pass. Note that the slot isn't centered on purpose.

Place a small amount of epoxy into the 3/16" hole. Insert the 5mm magnet into the hole. Use a 3/8" dowel to press the magnet flush with the top of the 3/8" hole. To set deeper, use a punch or other small diameter instrument to push the magnet to the desired level. Repeat for the other side.

Repeat Fit Check - Place/align Dowel back into Block. Drop balls back into the holes. This time they won't come out easily. For removal, smack the puzzle against a surface. Repeat for other side. Good news, you are done with the hard part :).

There are two types of plugs used. One style is decorative and acts as a decoy while the other, "B" holes, contains another magnet. For the magnet version, drill a 3/16" hole in the center per the drawing. Add the magnet similar to the 1.25" Dowel. You will need to make two of these. For the plugs, cut the 3/8" Dowel to 3/8" long sections. You will need seven of these.

The "C" hole on the front is a decoy (no functionality) but does serve a purpose. Since the puzzle is symmetric, this hole/plug identifies the sides with the magnets. To add a little fun, I drilled the hole 1.5" deep and dropped a ball in it. This is the only ball that will move when you shake the puzzle.

Note that this drawing also shows section views through the locking portions of the puzzle.

Although mostly decorative, the chamfers do help with handling since you will be smacking the puzzle using your hand. The chamfers shown are only about 1/4". You might want to consider making them larger to reduce the size/weight of the puzzle.

I sanded all sides with 220 grit paper. When sanding the ends, remember to keep the Dowel in the block. This will assure that the locking alignment doesn't move. After sanding, I applied an oil finish. Note that these pictures are pre-finish.

Although I've already discussed it, the solution involves smacking the block against the two correct faces as shown in the video. This allows the balls to drop into the unlocked position. The 3/8" Dowel on the one end references the sides where the ball will be recessed (unlocked). The ball rolling back and forth in that hole is just a decoy.

Once locked with both balls, it should be a challenge for anyone to figure it out. With two locks, you don't know when you have reached half the solution. In addition, you might inadvertently set it back to lock with more smacks. Knowing the correct sides to hit is the key to solving it.

Here is the completed puzzle. The oil really made the contrasting wood layers pop. .

I'm happy with how it turned out. There are a couple of changes I would consider if I made another. The first is the size. I happen to have a 1.25" Dowel in my shop so that drove the overall dimensions. Scaling to 2.5" cube (or smaller) would make handling easier. The second change would be to hide the holes on the sides since these give you a hint about the locking mechanism. The solution here would be decorative inlays on all four sides that ran the length of the block.

I plan to design a 3D print version in the next few weeks that will incorporate these changes along with some extra features. Stay tuned and thanks for viewing!