Tech Talks

How to properly secure bearings part 3: anti-rotational features

Tech Talks by igus helping solve design engineering problems with motion plastics

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tech talk Learn more at Part Three: Anti-rotational features Part two of this tech talk series reviewed how to secure bearing axially to keep them moving from their housings. Another important aspect of bearing security is the anti-rotational feature and why it is necessary. How to properly secure bearings Why would an anti-rotational feature be needed? In a plain bearing system, the press-fit in the housing hole keeps the bearing in place. The bearing supports the moving shaft, and the low coefficient of friction on the inner diameter of the plain bearing allows the shaft to easily rotate. Since the plain bearing is usually much less expensive than the shaft, it is designed to be a wear part. This means the plain bearing just needs to be replaced every so often, and not the more expensive shaft. Many metal plain bearings are lined with a thin PTFE layer on the inner diameter. The metal outer layer serves as the backbone of the bearing, while the PTFE layer keeps the shaft running smoothly. Plastic bearings, however, are more flexible. They offer sliding capabilities on both inner and outside diameter. In theory, it does not matter if the shaft rotates inside or if the bearing itself turns in the housing. Keep things spinning It is significant if the plain bearing rotates around the shaft in the housing, or if the bearing remains still and the shafts turns inside of it. Typically, shafts are optimized for sliding. Housing holes are not. The machining quality of housing holes is often quite cheap. They are simple holes drilled into a piece of metal, stamped or cut by lasers. Creating holes with a smooth inner diameter is expensive, and the surrounding material of the hole is usually a cheap construction steel or sheet metal. All these circumstances are essentially a collection of nonstarters for wear or sliding components, which is why the bearing should not turn with the shaft in the housing hole. While the bearing itself will not have a problem running on its outer diameter, the surface it will run on will. Both sliding surfaces in a bearing system are of equal importance. If the metal sliding surface is too rough and abrasive, the bearing will suffer from highly increased wear, resulting in more frequent downtimes or even damage to the bearing system. This is why a classic press-fit, non-rotating plain bearing with a rotating shaft inside is ideal. It is also why alternative methods should be prepared, if a press-fit cannot be maintained.

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