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How’s It Made? – Ball Bearings

How’s It Made? – Ball Bearings
By Bill Dickson February 29, 2016 12835 Views

Ever since antiquity, humans have used rollers to help move an object from one place to another. In ancient times, people used sticks and logs. That eventually evolved into wheels, although wheels would suffer wear and tear from constant grinding.

The ball bearing design evolved over the 19th century and eventually was refined to fit both bicycles and automobiles. Today, bearings come in all shapes and sizes. This week on How It’s Made?...the web staff here at Tool Parts Direct takes a look at how ball bearings are made.

Brief History

A Ball Bearing Factory in England during World War I

While ball bearing designs were used and found in Greek and Roman ships, the first modern ball bearing design was created by Welsh Iron Master Phillip Vaughn in 1794. His design helped stabilize a carriage’s axle as the ball ran along the track assembly. Ball bearings also took on greater importance throughout 19th and early 20th century production as bicycles and automobiles became a staple on everyday life.

Ball bearing also became vital during World War 1 and World War 2 as tanks and military vehicles went into production to help with the war effort. Today, ball bearings are used in most modern appliances and transportation. This includes automobiles, airplanes, ships and even some computers.

Materials and Design

The ball bearing very simply is a rolling-element bearing that uses balls to maintain separation between the bearing races. The ball bearing design reduces the friction and supports the radial and axial loads. As demonstrated above, once race is stationary while the other rotates along. The balls separating the races rotate along the track which reduces friction and strain compared to two flat surfaces sliding against one another.

Because of the stress and pound the bearings have to take, almost all bearings are made of steel. That also means that most bearings have 1% chromium and 1% carbon. The steel is also heat treated. Some cages are also made of hardened plastic because it’s easier to make and cheaper than other materials.

The Manufacturing Process

There are four major parts to building a ball bearing: the outer race, the rolling balls, the inner race and the cage that holds everything together.

When it comes to the races, both are made almost the same way. Since they both are steel rings, steel tubes are created and whittled down to the appropriate size. Those steel tubes are inserted into cutting machines that cut the tool into its basic shape…leaving them a little bigger than they should be. This is so the races can be heat treated before they’re finished as steel usually warps during the process. They are then treated back to their original size.

The rough cuts are put into an oven and are heated over 1500 degrees Fahrenheit for several hours. They are then dipped into an oil bath to cool them and make them very hard. The races are then tempered when they are inserted into an oven that’s about 300 degrees Fahrenheit. The heating process makes the races tough and hard. After the heat treatment process, the races are put into grinding wheels. Every race is fed into the grinders which leaves a very smooth and accurate surface.

Graphic Courtesy of Made How

As for the balls, the balls have a simpler design, but can be more difficult to make. The balls start out as a thick wire. This wire is fed into a roll machine which cuts off a short piece and smashes both ends in toward the middle. This process is called cold heading. After the balls are smashed, little lines show up on the sphere called “flash.”

The flash needs to be removed and the bearings are put between the faces of the two iron disks where they ride in grooves. The inside of grooves are rough and it tears the flash off of the balls. One wheel rotates while the other stays in place. The stationary wheel has holes in it so the balls can be fed into and out of the grooves.

A conveyor feeds the balls into one hole, rattles in the slot and comes out the other side. Those balls are then fed back onto the conveyor through the wheel grooves and the flash is completely removed. The balls are left oversized so they can be ground to their proper finished after heat treatment.

Graphic Courtesy of Made How

The heat treatment process is very similar to what the races used. The balls become tough and hard after heat treating and tempering. Once that’s finished, the balls are put into another machine that grinds the balls to a smooth, mirror-like finish. After that, an abrasive compound is pressed on as well.

The steel cages are next and those are stamped out of fairly thin sheet metal. The cages are then bent into their final shape in a die. Plastic cages are made in the injection molding process. A hollow metal mold is filled by squirting melted plastic into it. The machine lets it harden and once the mold is opened up, the finished cage is taken out and ready for assembly.

Photo Courtesy Made How

Once all the parts are created, it’s time for assembly. First, the inner race is put inside the outer race…only off to one side as far as it can be. This makes a space between them on the opposite side which is large enough to insert the balls into the grooves. The cage is installed to hold the balls away from each other. Plastic cages are snapped together while the steel cages are riveted together. Once the bearing is assembled, it’s coated with a rust preventative and packaged for shipping.

Photo Courtesy of Tien Gan Thuat


Ball bearings will be used for many years to come since they are both simple and cheap to create. Make sure you keep an eye out for future content from all the web staff here at Tool Parts Direct.