How yo-yos are made

One yo-yo patent press-fits its nut after molding, since a brass nut molded in makes rejects impossible to recycle.

stations: 8
things upstream: 52
raw sources: 18
steps from the ground: 8

The short version

Two routes show up in patents and machine shops. Plastic halves shoot from injection molds, with a threaded nut molded in or pressed into a socket afterward. Metal halves are turned on a CNC lathe from aluminum bar, hollowed out and tapped. Either way, an axle joins the halves, the string loop goes on, and one half screws onto the other.

Machine the molds

Molds are modeled on a computer and cut from solid metal. Student teams in an MIT manufacturing course mill theirs from aluminum billets, then load them into a 30 ton injection molding machine.
Shoot the plastic halves

Plastic is injected into the closed mold to form each half. A conventional setup places a threaded insert on a core pin first. Yomega's patent molds a hexagonal socket instead, so continuous automated machines can run without anyone loading inserts.

Goes in
Plastic
Press in the nut

A hexagonal threaded nut is pressed into the socket, guided by a shallow wider recess at its mouth. Its corners stop it turning. Because it goes in later, it can be steel like the axle, which makes stripped threads less likely.

Goes in
Steel
Turn the metal bodies

Metal yo-yos start as blanks sawn from 2.5 inch 6061 aluminum round. In one CNC lathe project, tools turn the outside, drill and tap the center, bore out the inside, then cut the final profile and part it off. A small pip left behind gets filed away.

Goes in
Aluminum
Stick on response pads

Self-adhesive pads go on the inner face of each metal half, centered as closely as possible. They let the yo-yo grip the string and climb back to the hand.
Seat axle and bearing

A threaded center shaft screws into one half and a ball bearing presses onto its shoulder. The bearing reduces friction, so a skilled player can keep a yo-yo spinning for minutes, where a fixed axle lasts 10 to 20 seconds.

Goes in
Ball bearing
Loop on the string

String made from one twisted length is untwisted slightly at its end to open a loop, which drops over the bearing. It sits loose, so the yo-yo can spin at the bottom of a throw.

Goes in
Sewing thread
Screw the halves together

The second half threads onto the shaft and closes around the string. Plastic halves often also get a thin cover, which student teams vacuum-form separately.

End of the lineYo-yo

Worth repeating

Yo-yos were known to ancient Greeks and appear on vase paintings. Examples survive in bronze and fired clay.
By November 1929 Pedro Flores's factories in California employed 600 workers, making 300,000 units a day.
A court case in 1965 decided that yo-yo had become common speech, so Duncan lost exclusive rights to the name.