Gear and Gear Cutting Components

Our gear units have quite a choice of gear-cutting and gear-forming techniques at their disposal, including hobbing, shaping, grinding, broaching, milling and rolling. Every production process is inevitably a compromise between ease of machining, good surface finish, profile accuracy, speed of output and economic production. All metal-removal operations leave minute ridges and scratches, caused by tool shapes or by the motion of rotary cutters; ‘perfect’ profiles and finishes are not obtainable with normal industrial processes. Tooling marks and deep scratches act as stress raisers, which occasionally lead to fatigue failure and tooth breakage. Such a failure almost invariably starts in the fillet radius at the root of a tooth, and may be caused by the use of a cutting tool with too small a radius.

Most gears benefit from careful running-in under light load, since in this way the teeth acquire the surface finish needed for good lubrication and smooth running. In effect, they are given a final production operation, without which the process of surface failure might be initiated as soon as service operation begins.

The life of a gear can also be limited by poor assembly. If a pinion is clumsily pressed onto a shaft, for example, it is likely to operate in an overstressed condition and fail at an early stage, even through running well within its designated rating.