What you will need:
- ¾” x ¾” wood stock
- 3/16” metal dowel
- 1/4” drill bit
- 5/16” drill bit
- Wood glue
- Adult supervision
PLEASE NOTE: This activity will require the use of power tools such as a drill and possibly a table saw. Power tools should ONLY be operated by responsible and trained adults.
- Cut two pieces of wood 8” in length from your ¾” stock
- Cut four pieces of wood 3 5/8” in length from your ¾” stock
- Drill a ¼” hole 1 ½” deep in the center of one end of each 3 5/8” piece as shown. Since the holes must be centered and drilled straight into the wood parallel with the sides of your stock, it is best to use a drill press for this step.
- Cut four pieces of your 3/16” diameter metal dowel 1 ¼” in length. Sand ends to make sure that they are smooth and nicely rounded after cutting.
- Place one metal dowel into each hole that is drilled in the ends of each of your 3 5/8” pieces of wood as shown. This piece should fall all the way into the hole and end up ¼” deep since the hole is ¼” deeper than the dowel.
- Glue two of your 3 5/8” pieces onto one of your 8” pieces as shown. Make sure that you leave a big enough gap between these two pieces that another piece of ¾” stock fits easily in between them as shown. Clamp until glue is dry. Also, make sure that your metal dowels are already inserted into these pieces before gluing them in place as you will not be able to insert them once the glue has set
- Repeat step #6 with your remaining pieces of wood
- Mark the center of your hole on the outside edges of your puzzle pieces as shown (on both puzzle pieces)
- Make sure that all of the pins are pushed in and fit the two pieces together as shown.
- Mark each piece where you need to drill using the lines that you previously marked to indicate where your pins are located. See illustration below:
- Take the two puzzle pieces apart and use the lines that you just drew to determine where you need to drill your hole to allow the pins to slide through and lock the puzzle pieces together. Drill a 5/16” hole at this point as shown:
Repeat these steps to do the same for your other puzzle piece. Erase all of your pencil lines and sand your puzzle smooth.
- You may now put your puzzle pieces together by pushing all of the pins in and fitting the two pieces together as shown. Once they are together, simply tilt the puzzle in any direction to lock the pieces together. The only way to get the pieces apart is to now spin the puzzle quickly to push all of the pins outward. Have fun!
What is going on?
By inserting four pins into the puzzle pieces during the build, no matter which way you tip the puzzle, you will always have at least one pin that is going through the other piece making it impossible to pull them apart. Since gravity is constantly pulling on the pins when you tip the puzzle from side to side, the only way to get all four pins to go slide outward (unlocking the puzzle) is to spin it quickly. By spinning the puzzle, you are applying a force known as centrifugal force to each pin. Newton’s first law of motion is known as the law of inertia. This law sates that everything has inertia and remain in a state of rest or uniform motion until another outside force is applied. Basically, anything in motion will continue in a straight line unless it is affected by another force. When we spin an object in a circular motion, we not only put the object in motion but we are constantly changing its direction. The objects in question (each pin in this case) want to travel in a straight line which causes each pin to be pushed outward, away from the center of the puzzle.
You may have noticed in the video that I had also built a square piece that the two puzzle pieces fit into. This is an optional piece that makes this puzzle a little more interesting for people to figure it out. Simply put the two puzzle pieces together to determine what size you need to make it so that they will just barely fit. If you made your puzzle to the dimensions listed above, you should be able to make a wooden square (from ¾” stock that has an opening that measures 1 ¾” x 2 ¼”