https://www.youtube.com/watch?v=PLkKVC_n0Go "Simple Secret Box II: Coin Bank" is a coin bank with a secret locking mechanism. Like my Apple Coin Bank design, this model was designed to teach the grandkids to save money, but includes an additional feature; if they change their minds and wish to make an "early" savings withdrawal, well, I didn't shown them how to open the bank. Featuring dovetail fixed joinery, and a sliding dovetail top, the trick to opening the box is, well, you'll figure it out eventually... The locking mechanism is based on the German designed "Radbox" ("rad" in German translates to "wheel" in English) that incorporates two mirror image slotted wheels in an ingenious manner to keep the box closed. While the design of my locking mechanism is more "cam" shaped than "wheel" shaped, the principle of operation is the same. And as in the original design, the locking mechanism remains hidden from view, even when the box is opened. I could not locate the original designer for this mechanism, so if anyone has their name I would be grateful for it in order to give them proper credit for their ingenious design. There are no batteries, power supplies, motors, springs, computers, wiring or any other hardware required to build this model, just 3D printed parts, which is one of the many reasons I truly enjoyed designing, printing, assembling and testing Simple Secret Box II: Coin Bank. As usual, I probably forgot a file or two or who knows what else, so if you have any questions, please do not hesitate to ask as I do make mistakes in plenty. Designed using Autodesk Fusion 360, sliced using Cura 3.4.1 and printed in PLA on both an Ultimaker 2+ Extended and an Ultimaker 3 Extended.