Machinery's Handbook, 31st Edition
CHECKING GEAR SIZES
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Table 7. Checking External Spur Gear Sizes by Measurement Over Wires EVEN NUMBERS OF TEETH Dimensions in table are for 1 diametral pitch and 1.68-inch series wire sizes (a Van Keuren standard). For any other diametral pitch, divide dimension in table by given pitch. Wire or pin diameter Diametral Pitch 1.68 = No. of Teeth Pressure Angle 14 1 ∕ 2 ° 17 1 ∕ 2 ° 20 ° 25 ° 30 ° 104 106.2901 106.2685 106.2642 106.2788 106.3136 106 108.2905 108.2688 108.2644 108.2789 108.3137 108 110.2910 110.2691 110.2645 110.2791 110.3138 110 112.2914 112.2694 112.2647 112.2792 112.3139 112 114.2918 114.2696 114.2649 114.2793 114.3140 114 116.2921 116.2699 116.2651 116.2794 116.3141 116 118.2925 118.2701 118.2653 118.2795 118.3142 118 120.2929 120.2703 120.2655 120.2797 120.3142 120 122.2932 122.2706 122.2656 122.2798 122.3143 122 124.2936 124.2708 124.2658 124.2799 124.3144 124 126.2939 126.2710 126.2660 126.2800 126.3145 126 128.2941 128.2712 128.2661 128.2801 128.3146 128 130.2945 130.2714 130.2663 130.2802 130.3146 130 132.2948 132.2716 132.2664 132.2803 132.3147 132 134.2951 134.2718 134.2666 134.2804 134.3147 134 136.2954 136.2720 136.2667 136.2805 136.3148 136 138.2957 138.2722 138.2669 138.2806 138.3149 138 140.2960 140.2724 140.2670 140.2807 140.3149 140 142.2962 142.2725 142.2671 142.2808 142.3150 142 144.2965 144.2727 144.2672 144.2808 144.3151 144 146.2967 146.2729 146.2674 146.2809 146.3151 146 148.2970 148.2730 148.2675 148.2810 148.3152 148 150.2972 150.2732 150.2676 150.2811 150.3152 150 152.2974 152.2733 152.2677 152.2812 152.3153 152 154.2977 154.2735 154.2678 154.2812 154.3153 154 156.2979 156.2736 156.2679 156.2813 156.3154 156 158.2981 158.2737 158.2680 158.2813 158.3155 158 160.2983 160.2739 160.2681 160.2814 160.3155 160 162.2985 162.2740 162.2682 162.2815 162.3155 162 164.2987 164.2741 164.2683 164.2815 164.3156 164 166.2989 166.2742 166.2684 166.2816 166.3156 166 168.2990 168.2744 168.2685 168.2816 168.3157 168 170.2992 170.2745 170.2686 170.2817 170.3157 170 172.2994 172.2746 172.2687 172.2818 172.3158 180 182.3003 182.2752 182.2691 182.2820 182.3160 190 192.3011 192.2757 192.2694 192.2823 192.3161 200 202.3018 202.2761 202.2698 202.2825 202.3163 300 302.3063 302.2790 302.2719 302.2839 302.3173 400 402.3087 402.2804 402.2730 402.2845 402.3178 500 502.3101 502.2813 502.2736 502.2850 502.3181 Allowance for Backlash: Table 1, Table 2, Table 7, and Table 8 give measurements over wires when the pitch diameters are correct and there is no allowance for backlash or play between meshing teeth. Backlash is obtained by cutting the teeth somewhat deeper than standard, thus reducing the thickness. Usually, the teeth of both mating gears are reduced in thickness an amount equal to one-half of the total backlash desired. However, if the pinion is small, it is common practice to reduce the gear teeth the full amount of backlash and the pinion is made to standard size. The changes in measurements M over wires, for obtaining backlash in external spur gears, are listed in Table 9. Table 7. (Continued) Checking External Spur Gear Sizes
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