That stupid locket from "The Illusionist".
Turn one half 180 degrees on a pivot...
Wow! It's a heart.
Slide the top open and reveal the picture of your love. Of course it's ripped in half and the movie used two separate prop lockets, neither of which worked fully.
I used this sketch from Curious Goods to do the layout and general geometry.
One half of my locket.
The other half.
The pivot pin is pinned to one of the halves. In either the open or closed position a spring bullet catch holds it against rotation. I would probably use a shallower detent than I show.
My sneaky half hinge. The undercut groove is essential. Each of the pair pinned to the one of lid halves of the locket.
The pin (and glue, probably) holds the half hinge to the lid half. The bent spring tongue slides in the groove of the half hinge, holding it to the bottom half while allowing rotation. You could use a half dovetail groove, a undercut boss on the bottom and a pin riding in a groove or sundry other methods, but any solution must hold the pin down and against the semicircular pocket while allowing it to rotate, and for the other half hinge to rotate into it and be retained as the top halves are turned to open.
The bent spring tongue is shown in the semicircular pocket in the bottom half. Notice the detent for the spring bullet catch.
A&B: half hinge, C&D: The bent spring tongues, E&F: pins to hold the half hinges to the top halves. G&H: parts of the bullet spring catch (should be secured to the pocket somehow so it doesn't shoot out when opened.) I: pin to hold pivot pin in one half of the bottom halves, J: Pin rides in groove in pivot pin to keep it in position so it has no axial play.
The 4 halves.
The 4 halves.
Well, what do you think, would it work? It is certainly doable. The lid halves are not mechanically joined, but are restrained against each other with the same axis of rotation.
This would take a lot of fine lathework under a microscope, more like clockmaking than carpentry. I have no intention of trying to make it. I'm sure it needs a lot of experimental refinement...
EDIT/UPDATE: See here for a design that uses common materials and can be made with hand tools...
(copyright 2007 Nick Carter)
