Gear teeth pitch measurements

Gear backlash is the play between teeth measured at the pitch circle. It is the distance between the involutes of the mating gear teeth, as illustrated in Figure 39.17. 

Backlash in gears is the play between teeth that prevents binding. In terms of tooth dimensions, it is the amount by which the width of tooth spaces exceeds the thickness of the mating gear teeth. Backlash may also be described as the distance, measured along the pitch line, that a gear... 

Circular Circular pitch is the distance from a point on one tooth to the corresponding point on the next tooth measured along the pitch circle as shown in Figure 57.32. Its value is equal to the circumference of the pitch circle divided by the number of teeth in the gear. While most common-size gears are based on diametric pitch, large-diameter gears are frequently made to circular pitch dimensions. 

A similar measurement is illustrated in Figure 14.13, along the pitch line of a gear. The diametrical pitch being the number of teeth in 3.14l6 inches of pitch line, the gear in this illustration is also a 10 diametrical pitch gear. 

Count the number of teeth in the gear and divide this number by the measured pitch diameter. The pitch diameter of the gear is measured from the toot or bottom of a tooth space to the top of a tooth on the opposite side of the gear. 

Figure 14.15 illustrates a gear with 56 teeth. The pitch diameter measured from the bottom of the tooth space to the top of the opposite tooth is 5 inches. Dividing 56 by 5g gives an answer of 9-jg inches, or approximately 10. This method also indicates that the gear is a 10 diametrical pitch gear. 

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