Chapter 13 - Gears and Gearboxes

Abstract

This chapter provides a complete overview of gears and gearboxes. A gear is a form of disc or wheel that has teeth around its periphery for the purpose of providing a positive drive by meshing the teeth with similar teeth on another gear or rack. This chapter also highlights spur gear. The spur gear might be called the basic gear, since all other types have been developed from it. Its teeth are straight and parallel to the center bore line. Spur gears may run together with other spur gears or parallel shafts, with internal gears on parallel shafts, and with a rack. This chapter also discusses pitch diameter and center distance; pitch circles have been defined as the imaginary circles that are in contact when two standard gears are in correct mesh. The diameters of these circles are the pitch diameters of the gears. The center distance of the two gears, therefore, when correctly meshed, is equal to one half of the sum of the two pitch diameters. A specific type of pitch designates the size and proportion of gear teeth. In gearing terms, there are two specific types of pitch: circular pitch and diametrical pitch. Circular pitch is simply the distance from a point on one tooth to a corresponding point on the next tooth, measured along the pitch line or circle. Large-diameter gears are frequently made to circular pitch dimensions. Pitch calculations are also discussed in this chapter.