Gear teeth pitch diameter

As no commercial master gear with pitch diameter d =1.3mm was found, it was decided to increase the master gear diameter to d=30mm resulting in a teeth number z=300 (Table 3). 

Diametrical pitch, usually a whole number, denotes the ratio of the number of teeth to a gear s pitch diameter. Stated another way, it specifies the number of teeth in a gear for each inch of pitch diameter. The relationship of pitch diameter, diametrical pitch, and number of teeth can be stated mathematically as follows. 

Basically, two engaging gears are two cylinders of different diameter with teeth machined on their periphery (Fig. 29-82). A gear is defined by its basic diameter (pitch diameter), its width, the number of teeth, and the angle that the teeth make in respec t to the axis. 

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). 

Example 1 What is the circular pitch of a gear with 48 teeth and a pitch diameter of 6 inches ... 

Example 2 What is the pitch diameter of a 0.500-inch circular-pitch gear with 128 teeth ... 

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

One problem faced in the model realization was the selection of the master gear to be used in the roll test. Both normal modules for micro gear and master gear should be equal, m=0.1 and given this value the pitch diameter d and number of teeth z for the master gear could be defined. 

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. 

Circular pitch is the distance from a point on a gear tooth to the corresponding point on the next gear tooth measured along the pitch line. Its value is equal to the circumference of the pitch circle divided by the number of teeth in the gear. The relationship of the circular pitch to the pitch-circle circumference, number of teeth, and the pitch diameter may also be stated mathematically as follows ... 

Fovir gears, 48 pitch, l/4 in. bore, clamp hub 72 teeth, anti-backlash, SR 414253-72 (Reeves Catalog No.), pitch diameter 1.5000 ... 

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