How ball bearings are made

A bearing ball starts as a chopped piece of wire, squeezed in a machine named for making nail heads.

stations: 9
things upstream: 29
raw sources: 13
steps from the ground: 6

The short version

A ball bearing is two grooved steel rings with a ring of hard steel balls between them. Balls are cold-headed from wire, rolled free of flash, hardened, ground and lapped. Rings are cut from tube, hardened and ground. The inner ring goes inside the outer, balls drop in, and a cage spaces them.

Head balls from wire

A heading machine slams two hemispherical dies onto a slug of wire with no added heat. The result is a rough ball with a ring of excess metal, called flash, around its middle.

Goes in
Steel wire
Roll off the flash

Balls run through the grooves between two cast iron plates, one spinning and one still. The rough grooves tear off the flash and leave a slightly oversized ball.
Cut the rings

Automatic machines cut steel tube to the basic shape of the inner and outer rings, leaving extra metal to allow for warping in the furnace. Outer rings are stamped with the bearing number.

Goes in
Steel
Harden everything

Rings and balls are heated, cooled in oil and tempered in a second oven, so they carry loads without denting.

around 1550 degrees F
Grind the races

The hardened rings are now too hard to cut, so wheels grind their width, radius and groove to size.
Grind and lap the balls

Balls are ground to size, then roll between soft cast iron plates under low pressure with a polishing paste, until the surface is smooth.

8-10 hours lapping
Stamp the cage

A press cuts the cage outline from thin sheet metal, and a die bends it to shape. Some cages are injection molded from plastic instead.

Goes in
Sheet steel
Load and close

The inner ring goes inside the outer ring, balls drop into the gap and are spaced evenly, and the cage is snapped or riveted in to hold them apart.
Grease and seal

The bearing is coated with a rust preservative or packed with grease, then fitted with shields or seals and boxed.

End of the lineBall bearing Next it goes into electric motor, washing machine, locomotive and 6 more.

Worth repeating

Philip Vaughan of Carmarthen, Wales, was awarded the first recorded patent on ball bearings in 1794.
In 1869, the winning bicycle in the first road race, Paris to Rouen, carried the first radial ball bearing, designed by Jules Suriray.
Finished bearing balls can be held to tolerances as small as a millionth of an inch.