3D Printed 'Centrifugal Puzzle Box' - Solved With a Spin...

With the freedom of 3D printing, I wanted to design something brand new, innovative and that to my knowledge does not exist anywhere else in the world, but it also had to be small enough that is did not cost too much to 3D print (I use an online service called Shapeways to 3D print my designs as I don't own my own a 3D printer (yet?) and this can get very costly) so this is what I came up with, a puzzle box that is solved in a unique way like no other in the world, most puzzle boxes I have seen are solved in a number of moves by moving parts of the puzzle to certain precise locations in a certain order to open the box so I wanted to make mine different... by simply spinning the box on a flat surface will unlock the box's lid however I didn't want this solution to be easy to discover so many distractions were added along the way in the design process, as well as a clue towards the solution of the puzzle in the form of a key-ring.

Above is a time lapse animation of me modelling the bottom half of the box, this was the simplest section to model so it is the easiest to show a time lapse of it's creation.

I first designed the mechanism for this puzzle box on my iPad using a simple drawing application and then proceeded to design the final box using Autodesk Inventor (CAD software), the hardest part of the design process was not the modelling itself, it was calculating all of the exact dimensions every feature such as the channels and loops should have to be so that these 6mm ball bearings would move freely within their channels and would cross the loops in the lid when the lid is on and the ball bearings are at the inside edge of their channels to lock that loop and stop the lid from being removed. I made a clearance of 0.25mm between any parts that were designed to fit into each other such as the pins/rods in the lid and holes in the box so they could fit into each other after printing with a close fit but not too much friction.

I decided that the box had to look complex on the outside to distract from the deceivingly simple solution so I decided to add 6 sliders to the top of the lid of different shapes and also 3 sprung buttons (in the second prototype) by taking advantage of the 3D printing material's flexible nature meaning I can model springs for the buttons that will be built into the design and printed as one piece, these added design features have absolutely no purpose towards solving the puzzle, they are simply a distraction for the user. Some 3D printing techniques such as the one I will be using (SLS) can print fully assembled assemblies in one print and I am taking advantage of this by designing the movable sliders and buttons within the lid of the puzzle box by making sure I leave a clearance of 0.5mm between the physically separate parts of the design (e.g. the lid and a slider) so they will actually be separate objects after printing, this removes the need of assembly after printing and also makes the sprung buttons that are part of the design possible.

Finally I decided to add a clue towards the solution of the puzzle, this is in the form of the numbers round the top of the lid, these are actually coded in the format A=1 B=2 C=3 to read 'GIVE ME A RAPID SPIN TO UNLOCK MY LID', yes, this is difficult to notice however I also modeled a 3D printable key-ring that contains a QR code which can be scanned by a smartphone to reveal the text 'A=1 B=2 C=3' to guide the user to this clue if they wish. After a few solid hours of modelling I was ready to order a prototype from Shapeways (3d printing service)

I learnt that a few things that needed modifying on the first design but thankfully after a bit of modification the prototype worked!

Unfortunately the design didn't work straight away, I had overestimated the grippyness of the material so even when the lid was locked, I could remove the lid as the friction between the ball bearings and the outer walls of their channels was not enough to stop the lid being removed, this was fixed by adding a lip to the inside end of the channels so now there was a physical barrier stopping the ball bearings from slipping out when the lid is locked and trying to be removed so was no longer relying on the friction of the material. This lip was created out of 1/4 mm fiberglass reinforced sheet which I glued into the channels to create a lip using cyanoacrylate (superglue).

The second failure was the text and numbers I had engraved into the box, due to the SLS (selective laser sintering) 3D printing process, the engraved letters  were unfortunately full of excess powder from the 3D printing process and this was nearly impossible to remove, this made the text quite difficult to see and overall made the puzzle box look a bit tacky, to fix this I decided to emboss all the text and the numbers so this problem of powder would not be a problem.

I also decided that on the next version to slope the front and back ends of the channels to make each ball bearing to only be in 1 on 2 positions (bistable) each channel to be either locked or unlocked making the locking mechanism more secure and reliable.

The keyring containing the QR coded clue of 'A=1 B=2 C=3' decodable using a smartphone printed perfectly and the QR code could be seen and read by using a smartphone.

I ordered a second prototype with these amendments and within 4 working days after the evening I placed the order it arrived!