The second music box I wanted to make was going to be part of a pirate-themed series of puzzles. I needed a box that plays “Yo-ho-ho”, or some other piratey song.
Also, I wanted to improve the design of the previous music box to make it easier to disassemble if something goes wrong.
To play a custom melody, I used a programmable player by Kikkerland: https://www.amazon.com/gp/product/B000HAUEFY
It comes with a punch tool and 3 blank paper strips.
The device is much larger than the fixed melody version, and the paper stirps take a lot of space. The approach from the previous music box was not going to work. I decided to use the paper strip itself to drive the lock
The strip is wrapped around a drum, which rotates as the music plays and in turn pulls on a fishing cord that unlocks the box.
To make the box easier to disassemble, the back wall is not glued in, but is attached by a pair of pins. The lid is also removable from its axis for easier access.
Here’s the final box
Locking the box
Attach the paper strip to the chain and wrap it around the drum. Insert the pointy end into the music device and turn the handle a few times until the strip shows up on the other end.
Insert the axle of the drum into the hole in the front wall. Attach the back wall to the box, while inserting the axle into the second hole.
Attach the two pins to secure the back wall.
Attach the lid to its axis.
Turn the hook to the unlocked position and insert a small pin in the front hole to keep the hook unlocked (I use the handle from the crank).
Close the lid and remove the pin to lock the box.
Resetting the box
After the box opens, detach the lid from its axis to get access to the pins holding the back wall. Remove the pins and remove the back wall. Carefully unhook the paper strip from the drum. Turn the handle to push the paper strip all the way out.
Emergency unlock
Insert a pin or a screwdriver in the bottom holes to push the pins up. This will free the back wall. Remove the back wall to get access to the insides.
Make it
This is the SVG file with the blueprints: music_box_v2.svg
The design assumes 3mm plywood and 4mm dowels. The locking pins in the back use 5mm dowels. If your supplies have different dimensions, you will have to adjust some of the measurements.
The holes for the music player fit M3 machine screws. The SVG has concentric circles around them with different colors. They are intended to be etched with varying laser power, to create a conical hole for the screw head.
The SVG file also contains the shape for the latch hook. You can cut it from plywood for the initial prototype, but I recommend you use a more sturdy material like plastic for the final part.
Additional materials: You will need some rubber bands for the latch and the lid. The paper strip is attached to the drum using a jewelry chain with clasps. One end is hooked to the drum with a piece of paperclip wire. It is recommended to insert thin nylon washers between the moving parts to reduce friction.
Some experimentation will be necessary with the length of the paper strip and the length of the cord to get the box to open at the desired time.
Note on the music player: The device I used has a limitation that it can’t play the same note quickly in succession. If your melody has 2 identical 1/8th notes one after another, you will have to change it.
This music box was part of a puzzle and for that reason features a detachable crank
If you don’t need the crank to be a separate piece, the mechanism can be simplified.