Infinite Spiral

Flip it like an hourglass. The purple ring slides down, and the golden spiral seems to pour endlessly out of its own frame. No magnets, no batteries, nothing hidden in the base — just gravity and geometry.

The secret

The ring's hole has the exact twisted shape of the 3-strand helix, like a nut on a very long screw. The helix isn't fixed: it rests on two needle-point pivots and spins with almost no friction. The heavy ring can only fall by turning the helix, and a spinning twist reads as endless motion along its axis — the barber-pole illusion. Hand it to someone and let them work it out.

Print Settings

Three parts, no supports, each in the orientation of the file: the half-frame twice (both halves are the same part), the helix upright with a 5 mm brim, and the ring is heavy enough to drive the helix.

Assembly

Screw the ring onto the helix, stand the helix on one pivot, drop the second half-frame over it: each peg goes into the socket of the other half. The helix has 0.8 mm of end play so it spins freely.

Size. 158 mm tall, 60 mm base. Helix Ø 20 × 120 mm, 60 mm pitch.

About the rings. The rings in the files are not spares: each has a different clearance on the helix. A tight one grips more and comes down slowly, a loose one drops fast. Which one suits you depends on your printer — a tenth of a millimetre of flow or squish is enough to change the feel — so try a couple on the short test piece first and keep the one that screws on by hand without forcing and still slides down on its own.