How are ball bearings made perfectly round

How Are Bearings Made?

There are four major parts to a standard ball bearing: the outer race, the rolling balls, the inner race, and the cage.

Races

Both races are made in almost the same way.

Since they are both rings of steel, the process starts with steel tubing of an appropriate size. Automatic machines similar to lathes use cutting tools to cut the basic shape of the race, leaving all of the dimensions slightly too large.

The reason for leaving them too large is that the races must be heat treated before being finished, and the steel usually warps during this process.

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They can be machined back to their finished size after heat treating.

 

Surprisingly, the rolling balls start out as thick steel wire. Then, in a cold heading process, the wire is cut into small pieces smashed between two steel dies.

The result is a ball that looks like the planet Saturn, with a ring around its middle called "flash."

• The rough cut races are put into a heat treating furnace at about 1,550

degrees Fahrenheit (843 degrees Celsius) for up to several hours (