Tiniest Ball Bearings

These diminutive orbs were collected as part of our Crazy Materials Golf open day, where they featured in the dramatically scaled-down and genuinely ‘mini’ microscopic golf hole. These steel balls measure 0.25mm in diameter and are used in the smallest commercially-available ball bearings. They are so small that you can barely see them without magnification, but if you gently shake their jar you will hear them tinkling around in there.

For as long as we have needed to move things around, we have used round objects as rollers to make the job easier. The Egyptians used logs as a way of moving large slabs of stone for the pyramids, and every kind of machine that deals with motion will make use of bearings to smooth its path and reduce friction. There are thousands of sizes and designs of ball bearings, but modern steel ball bearings are all manufactured in the roughly the same way: the process of starts with a metal wire, usually carbon steel or stainless steel, which is cut into sections and cold formed into a spherical shape by smashing it between two hemispherical dies. The ‘flash’ or ridge that is left by the forming dies is then removed by rolling the balls between heavy cast iron plates. The balls are then ground with a grinding stone, heat treated for hardness and descaled to remove any residues from the heat treatment process. Finally, the balls are ground, lapped and polished slowly and meticulously to tolerances of within 0.0025 millimetres.

Balls produced in this way are responsible for the smooth spinning of bike wheels and the functioning of hard drives and photocopiers, amongst many other things. Plastic, ceramic (e.g. silicone nitride) and jewel (e.g. sapphire) ball bearings are used where low density, chemical resistance or non-magnetism are required, and are responsible for the functioning of roll-on deodorants, watches and wind turbines.