Planetary Gear Spinner — No Bearing Needed, the Gears ARE the Bearing (Print-in-Place Herringbone Fidget)
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A print-in-place planetary fidget spinner with zero hardware: no 608 bearing, no screws, no assembly.
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- Printables
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- Other Toys & Games
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- Creative Commons — Attribution
Most planetary spinners hide a 608 bearing in the middle. This one doesn't need it — and that is the whole point of the design.
The gears ARE the bearing
Hold the center knob and flick the outer ring. Everything spins on the gear teeth themselves:
Radial: the four planets center the sun inside the ring. It cannot wobble off-axis, because the planets are always pressed between sun and ring.
Axial: every gear is herringbone (30° helix). The V-shaped teeth cage each part between its neighbours — hold the knob upside down, shake it, nothing falls out. The only motion the geometry allows is the one you want: rotation.
No bearing, no screws, no glue, no assembly. It leaves the print bed finished.
Verified, not hoped
The gear profiles are proper involutes (25° pressure angle), generated and checked by the included Python scripts. The check does not just test the assembly position: it simulates the full rotation of the ring and measures the minimum gap between tooth flanks at every step.
Minimum clearance, any position, any pair: 0.316 mm
Backlash tuned for FDM: the nozzle rounds every valley, so the teeth are thinned by 0.35 mm on purpose
Sun 18 : planets 14 : ring 46 — hold the sun and the ring does 1.39 turns per planet orbit
Print it
No supports, no brim. Flat print, 12 mm tall, zero overhangs (measured: 0.00 cm²).
0.2 mm layers, 3 walls, 10-15 % infill. PLA is perfect.
One critical setting: Initial Layer Horizontal Expansion = −0.15 mm. The squished first layer is the only thing that can weld the teeth together. Do not skip this.
Ø76 × 12 mm (21 mm with the knob), ~25 g, about 1.5 h.
First use: the parts may need a firm first twist to crack the tiny contact points — hold the knob and turn the ring hard once. After a minute of spinning it wears in and runs smooth.
No hardware
Nothing. The model uses no bearings, no screws, no magnets, no weights. Every part of the mechanism is printed in place.
Remix it
The OpenSCAD file is generated by the included Python scripts (perfiles.py computes the involutes, genera_scad.py writes the model, and verificar_engrane.py re-checks the clearances through a full rotation). Change the tooth counts or the module, run the verifier, and it will tell you whether your variant meshes before you waste any filament.