Many young engineers may wonder exactly what the difference is between a bearing and a bushing, and some may be too embarrassed to ask. In this post, we are going to track down the difference.
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Definition of Bearing
First of all, we need to clearly define the term bearing. The word comes from bear, of which one definition means to support (we are not talking about the animal). We know that bearings provide support to other machine elements by providing a supporting surface, or bearing surface. They also constrain relative motion and reduce friction.
Types of Bearings
They are many types of bearings, but plain bearings are the simplest (and oldest). They are sometimes described as a hole through which a cylindrical shaft passes. There are several types of plain bearings, and they are differentiated based on the type of relative motion and support they provide. For example, journal bearings consist of a shaft rotating on a bearing surface, and are sometimes called rotary bearings or radial bearings. Thrust bearings provide support surfaces for loads that act along the length of a shaft, and linear bearings provide support for linear motion. But how does this tie into the definition of a bushing?
Bushing and Bearing Metals
Bearings and Bearing Metals published in 1921 by Industrial Press provides some clarification regarding the difference between a bearing and a bushing. The author describes the simplest bearing as being a hole in the machine housing through which a cylindrical shaft passes, which bears strong similarity to the description of a plain bearing. This hole in the machine housing provides a bearing surface to support the shaft. Because of wear that can occur between the shaft and the bearing, a bushing is or lining is placed in the hole of the machinery. The bushing/lining can easily be replaced when needed, and the machine housing remains as is.
Not All Bearings are Bushings!
Based on this information and some common sense, we can say that a bushing is a type of plain bearing inserted or attached to a housing in order to provide a bearing surface. While a bushing may be a bearing, not all bearings are bushings.
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