Gear teeth diametric pitch

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. 

The ratio between the pitch diameter and the number of teeth is called the diametral pitch, and for two gears to mesh, they must have the same diametral pitch. The diametral pitch is standardized and is always an integer. For gears used in process machineiy, the diametral pitch varies between 6 (coarse) and 20 (fine). 

The size and proportion of gear teeth are designated by a specific type of pitch. In gearing terms, there are two types of pitch circular and diametric. 

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. 

Diametric The most commonly used method of gear specification is based on diametric pitch. Practically all common-size gears are made to diametric pitch specifications, which also designate the size and proportions of gear teeth. 

Diametric pitch is a whole number used to specify the ratio of the number of teeth in a gear to its pitch diameter. Stated another way, it specifies the number of teeth in a gear per inch of pitch diameter. For each inch of pitch-circle diameter, there are pi (jr = 3.1416) inches of pitch-circle circumference. Therefore, the diametric pitch provides the number of teeth for each 3.1416 inches of circumference along the pitch circle. 

Example 2 What is the pitch diameter of a 12 diametric-pitch gear with 36 teeth ... 

Example 3 How many teeth are there in a 16 diametric-pitch gear with a pitch diameter of 3 inches ... 

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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