How It Works

How are ball bearings made?

Ball bearings are in so many applications and despite being loosely involved in engineering myself, I would love to know how they are made. The surfaces are polished and yet perfectly spherical, so how do they do it?

Asked by SHB on the How It Works forum

Ball Bearings

There are quite a few different parts that make up a ball bearing, including races, a cage, and then the covering to protect the bearing. I think you mean the actual ball though.

The first stage in the process is a cold or hot forming operation; a thick piece of wire is fed into a machine where it is cut down by slicing sections off each side until it is quite small. The machine then slams two hemisphere cavities (a bit like a mould) into the piece of wire to make a ball shape. As a result of this process, the ball will have a ring of excess metal around it, called a flash, which needs to be removed. The ball also needs further polishing to make it perfectly round and smooth. The ball with the flash is then fed into another machine which rolls the ball around between two rill plates. Rill plates are two hard plates of steel which wear away the flash and smooths the surface of the ball.

The ball is then heated to harden it after which it undergoes a grinding process similar to that of the rill plates until it is ground down to its final, very accurate measurements which often require tolerances as small as a millionth of an inch. The last process is called lapping, which requires a similar machine that exerts less pressure combined with a polishing paste to give the balls their perfect shiny finish without further reducing their size.