Circular leaf spring for musicboxes etc.
Make your prints interactive, add some spring driven power ;)
Filaflex = optimal, PLA works too.

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draw a cross
draw 4 to 5 circles from same center.
erase bottom half
draw half circles on bottom part from one line end to the next, starting one off, so you get a spiral.
on the horizontal Cross Line, make markings so yo can draw the same spiral again, but with an offset in relation to the spiral u just drew.
the thicker the offset, the thicker the part, the harder the resistance of the spring will be.