Machinery's Handbook, 31st Edition
Spur Gearing 2225 Table 7. Addendums and Tooth Thicknesses for Coarse-Pitch Long-Addendum Pinions and their Mating Short-Addendum Gears—20- and 25-degree Pressure Angles ANSI B6.1-1968 (R1974) Number of Teeth in Pinion Addendum Basic Tooth Thickness Number of Teeth in Gear Pinion Gear Pinion Gear N P a P a G t P t G N G (min) 20-Degree Involute Full Depth Tooth Form (Less than 20 Diametral Pitch) 10 1.468 .532 1.912 1.230 25 11 1.409 .591 1.868 1.273 24 12 1.351 .649 1.826 1.315 23 13 1.292 .708 1.783 1.358 22 14 1.234 .766 1.741 1.400 21 15 1.175 .825 1.698 1.443 20 16 1.117 .883 1.656 1.486 19 17 1.058 .942 1.613 1.529 18 25-Degree Involute Full Depth Tooth Form (Less than 20 Diametral Pitch) 10 1.184 .816 1.742 1.399 15 11 1.095 .905 1.659 1.482 14 All values are for 1 diametral pitch. For any other sizes of teeth all linear dimensions should be divided by the diametral pitch. Basic tooth thicknesses do not include an allowance for backlash. Table 8. Enlarged Pinion and Reduced Gear Dimensions to Avoid Interference Coarse Pitch 14 1 ∕ 2 -degree Involute Full Depth Teeth Number of Pinion Teeth Changes in Pinion and Gear Diameters Circular Tooth Thickness Min. No. of Teeth in Mating Gear Pinion Mating Gear To Avoid Undercut For Full Invo- lute Action
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
1.3731 1.3104 1.2477 1.1850 1.1223 1.0597 0.9970 0.9343 0.8716 0.8089 0.7462 0.6835 0.6208 0.5581 0.4954 0.4328 0.3701 0.3074 0.2447 0.1820 0.1193 0.0566
1.9259 1.9097 1.8935 1.8773 1.8611 1.8449 1.8286 1.8124 1.7962 1.7800 1.7638 1.7476 1.7314 1.7151 1.6989 1.6827 1.6665 1.6503 1.6341 1.6179 1.6017 1.5854
1.2157 1.2319 1.2481 1.2643 1.2805 1.2967 1.3130 1.3292 1.3454 1.3616 1.3778 1.3940 1.4102 1.4265 1.4427 1.4589 1.4751 1.4913 1.5075 1.5237 1.5399 1.5562
54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33
27 27 28 28 28 28 28 28 28 28 28 28 27 27 27 26 26 26 25 25 24
24 All dimensions are given in inches and are for 1 diametral pitch. For other pitches divide tabular values by desired diametral pitch. Add to the standard outside diameter of the pinion the amount given in the second column of the table divided by the desired diametral pitch, and (to maintain standard center distance) subtract the same amount from the outside diameter of the mating gear. Long addendum pinions will mesh with standard gears, but the center distance will be greater than standard.
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