Machinery's Handbook, 31st Edition
CHECKING GEAR SIZES 2309 Measurements for Checking Internal Gears when Wire Diameter Equals 1.44 Divided by Diametral Pitch.— Table 3 and Table 4 give measurements between wires for checking internal gears of 1 diametral pitch. For any other diametral pitch, divide the measurement given in the table by the diametral pitch required. These measurements are based upon the Van Keuren standard wire size, which, for internal spur gears, equals 1.44 divided by the diametral pitch (see Table 5). Even Number of Teeth: For an even number of teeth above 170 and not in Table 3, proceed as shown by the following example: Assume that the number of teeth = 380 and pressure angle is 14 1 ∕ 2 degrees; then, for 1 diametral pitch, figure at left of decimal point = given number of teeth − 2 = 380 − 2 = 378. Figure at right of decimal point lies between decimal values given in table for 300 and 400 teeth and is obtained by interpolation. Thus, 380 − 300 = 80 (change to 0.80); 0.8803 − 0.8795 = 0.0008; hence, decimal required = 0.8795 + (0.80 × 0.0008) 0.88014. Total dimension = 378.880l4. Odd Number of Teeth: Table 4 is for internal gears having odd numbers of teeth. For tooth numbers above 171 and not in the table, proceed as shown by the following example: Assume that number of teeth = 337 and pressure angle is 14 1 ∕ 2 degrees; then, for 1 diametral pitch, figure at left of decimal point = given No. of teeth − 2 = 337 − 2 = 335. Figure at right of decimal point lies between decimal values given in table for 301 and 401 teeth and is obtained by interpolation. Thus, 337 − 301 = 36 (change to 0.36); 0.8776 − 0.8759 = 0.0017; hence, decimal required = 0.8759 + (0.36 × 0.0017) = 0.8765. Total dimension = 335.8765. Measurements for Checking External Spur Gears when Wire Diameter Equals 1.68 Di- vided by Diametral Pitch.— Table 7 and Table 8 give measurements M , in inches, for check- ing the pitch diameters of external spur gears of 1 diametral pitch. For any other diametral pitch, divide the measurement given in the table by whatever diametral pitch is required. The result shows what measurement M should be when the pitch diameter is correct and there is no allowance for backlash. The procedure for checking for a given amount of backlash when the diameter of the measuring wires equals 1.68 divided by the diametral pitch is explained under a subsequent heading. Table 7 and Table 8 are based upon wire sizes equal to 1.68 divided by the diametral pitch. The corresponding wire diameters for various diametral pitches are given in Table 6. Table 6. Wire Diameters for Spur and Helical Gears Based upon 1.68 Constant
Diametral or Normal Diametral Pitch
Diametral or Normal Diametral Pitch
Diametral or Normal Diametral Pitch
Diametral or Normal Diametral Pitch
Wire Diameter
Wire Diameter
Wire Diameter 0.09333 0.07636 0.070 0.060 0.0525 0.04667 0.084
Wire Diameter
2
0.840 0.672 0.560 0.420 0.336 0.280 0.240
8 9
0.210
18 20 22 24 28 32 36
40 48 64 72 80
0.042 0.035
0.18666
2 1 ∕
2
3 4 5 6
10 11 12 14 16
0.168
0.02625 0.02333
0.15273
0.140 0.120 0.105
0.021
… …
7 … … Pin diameter = 1.68 ÷ diametral pitch for spur gears and 1.68 ÷ normal diametral pitch for helical gears. To find measurement M of an external spur gear using wire sizes equal to 1.68 inches divided by the diametral pitch, the same method is followed in using Table 7 and Table 8 as that outlined for Table 1 and Table 2.
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