For his “mini tank” video, Ivan Miranda developed a very neat snap fastener. Adjacent segments of his tank treads are held together by a pin that runs through a series of holes alternating between tabs on the two segments, as is usual for a pin hinge. The surprising feature is how the pin is prevented from sliding out the end of the hole: it’s flexible, and the end of the hole is curved, so you create a matching curve in the pin as you begin to insert it into the hole, then move the curve along the pin to finish inserting it.
So far this is just a spring-loaded friction connection, like a screw fastener or a nail. The nifty bit is that there’s a notch cut into the outside of the curve for the end of the pin to snap into, once you insert it far enough. At this point the pin is pressed up against the notch at one end and the end of the hole at the other. So you have a snap fastener with a significant energy barrier to overcome in order to disconnect it.
In order to make the pin removable, Miranda includes another hole at right angles to the pin at the end of the notch, through which you can insert a rod to bend the pin back into the curve, and a smaller hole at the other end of the pin’s hole through which you can press the pin back out.
This seems like an astoundingly neat idea, and I don’t understand why I haven’t seen it before. It entirely eliminates the need for screw fasteners in such loose-fit cases, while being immensely more vibration-resistant than screws. If the end of the notch (or the pin) is slightly slanted, the bending force of the pin will produce a preloaded compression force on the pin.
It isn’t necessary for the pin to be entirely enclosed; for example, the tusk of a tusk tenon could be used as such a “pin” by merely sliding in a curved groove, or by pressing against two dowels protruding from the surface it slides against.
It’s not obvious how to do a precisely analogous thing in a 2-D cutting environment, since there’s no way to curve the holes through which a fastener slides. But if the fastener instead expands after sliding through two holes, or rather slots, we have a standard spring-hook fastener, which can also be built onto the edge of a panel to slide through a single other slot rather than through two separate slots.