NEMA17 Geneva Indexing Turntable

This is a desktop indexing table. A NEMA17 stepper turns a crank pin, and the pin drives a 6-slot Geneva star wheel. Each full turn of the motor moves the 140 mm platter exactly 60°, then the locking disc holds it still for the next 240° of crank rotation. The platter parks at the same six stations every time, even when step timing is loose. You can use it for photographing parts, as a pick-and-place feeder, as a rotary tool changer, or just to show how a Geneva drive works. The platter has an M3 hole pattern at every station for mounting fixtures.

The layout is simple. The motor bolts face-up under a 150 x 100 mm deck that stands on four legs. Its shaft carries the pin-and-locking-disc driver. The Geneva wheel, a spindle tube and the platter form a single rotating stack on two 608 bearings. That stack turns on a fixed 8 mm rod pressed into the deck. A pointer collar clamps to the top of the rod and does two jobs: it keeps the stack from lifting off, and it marks the active station. The wheel, tube and platter all use the same 3-hole M3 pattern on a 38 mm PCD, so the stack can only bolt together one way.

Assembly order:

1. Press M3 heat-set inserts into the tops of the 4 legs, the 3 holes in the Geneva wheel and the 3 holes in the spindle tube's top flange.
2. Screw the 4 legs under the deck corners with M3x12 bolts. Press the 8 mm rod into the deck boss so its bottom is flush with the deck underside, then tighten the boss set screw.
3. Bolt the NEMA17 face-up under the deck with 4 counterbored M3x6 bolts, so its pilot boss sits in the 22.5 mm hole.
4. Tap the 5 mm steel pin into the driver. Slide the driver onto the motor shaft with its bottom 1 mm above the deck, and lock it with the set screw on the shaft flat.
5. Press a 608 into the underside of the Geneva wheel and slide it down the rod until it rests on the deck pad. Rotate the driver by hand to check that the pin enters each slot cleanly.
6. Bolt the spindle tube onto the wheel (3x M3x10), press the second 608 into the top of the tube and push its inner race down onto the rod.
7. Bolt the platter onto the tube with 3x M3x6 in the counterbores. Then clamp the pointer collar on the rod top, resting on the upper bearing's inner race, with the pointer aimed at a station.

Tuning: one index is one full driver revolution, which is 200 full steps. For the smoothest start and stop, ramp speed so the fastest motion falls inside the 120° window when the pin is in a slot. Put a smear of grease on the locking disc rim and the wheel's concave arcs. If the pin binds, ream the slots with a 5.5 mm drill. There is 0.5 mm of running clearance everywhere in the Geneva geometry. For a repeatable home position, start with the motor parked at the middle of the dwell, pin pointing directly away from the wheel.