Living hinge

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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 bend 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.

Some researchers feel that, with proper design, an entire subassembly of 2 separate plastic parts and the nuts, bolts, bearings, etc. between them can be replaced by a single plastic part with such a Compliant-Link, eliminating the assembly time of that link and hopefully improving the doubling time of the whole system.

Researchers find that "Flexure parallel mechanism possesses high stiffness, high natural frequency, no-error accumulation, no-backlash, no-friction, no-need of lubrication, vacuum compatibility and high accurate motion with small range."[1]

Further reading

A view of the Delta-Pi carriage showing the 623ZZ bearings, live hinge design and spring beam for tension adjustment.