Living hinge

Many people treat the plastic parts printed by a RepRap or other FFF machine, or the plastic parts cut out of acrylic by a Laser Cutter, as more-or-less rigid items. If they need one thing to move relative to another, they make (at least) 2 separate plastic parts and add the appropriate hardware to enable that motion in the desired direction(s) and constrain the motion in other direction(s).

A few researchers are experimenting with making parts that are designed to move and flex. Some of them are relatively stiff parts that can be pushed very little -- only a few degrees, or only a fraction of a mm -- before they snap back into position. Others are relatively flexible parts that can be pushed much further -- a half-turn bend, or motion across several centimeters.

Further reading

• The snap-together joints of the MTM Snap
• Compliant Linear Motion Mechanism 1
• Sarrus Z Linkage
• Wikipedia: living hinge
• "lattice hinges" aka Snijlab-style living hinges, Sninges, laser-cut hinges. Has useful equations.
• "Laser-Cut Elastic-Clipped Comb-Joints". Has useful equations.
• "CalcBot Pen Holder" is a single printed part that acts like 3 separate parts: a clamp, a base, and a spring hinge between them -- a hinge formed from a single-layer bridge of rep-rapped filaments.
• "A snap-together RepRap? Faster, easier, and RP friendly?"
• "Pin Connectors by tbuser" openscad library script
• "Nautilus Gears" with a press-fit snap connector