Worm gearing . 6 54 WORM GEARS Worm: Number of threads 5 Pitch diameter <• in. Pitch circumference in. Length of worm 5 in. Lead 5. 9375 in. Lead angle 30° 11 Thread angle • 60° Length of thread per rev in. Rubbing speed p. s. Worm Wheel: No. of teeth 39 Pitch diameter , in. Pitch in. Subtended angle /3 (see table). The torque at the worm pitch line was kept constant at1990 lb. giving a normal tooth pressure of 4378 lb. The rubbing. BFJ speed was also nearly constant at ft. per second. Conse-quently the heat generated in friction (from equation 68,
Worm gearing . 6 54 WORM GEARS Worm: Number of threads 5 Pitch diameter <• in. Pitch circumference in. Length of worm 5 in. Lead 5. 9375 in. Lead angle 30° 11 Thread angle • 60° Length of thread per rev in. Rubbing speed p. s. Worm Wheel: No. of teeth 39 Pitch diameter , in. Pitch in. Subtended angle /3 (see table). The torque at the worm pitch line was kept constant at1990 lb. giving a normal tooth pressure of 4378 lb. The rubbing. BFJ speed was also nearly constant at ft. per second. Conse-quently the heat generated in friction (from equation 68, Chap-ter IX) was per minute and (from equation 73,Chapter IX) the area of rear axle surface should be sq. ft. THE WIDTH OF THE WORM WHEEL 55 The actual surface was approximately 11 ,sq. ft. Fig. 22 showsa section of the worm wheel of which the original value of /?was 107° 45; under these conditions^ the number of teeth incontact was 5 (equation 12, Chapter IV). The wheel was subse-quently cut down in width as shown in the figure. In Fig. 22, the gears are shown diametrically in sectipn andplan, the lines AB, CD, indicate the original width of the gearswith /3=107° 45. There are then five points of contact—a, b,c, d, and e. /3 was then reduced to 72° as shown by lines EF and points of contact are thus reduced to three—b, c, and d. P reduced again to 64°, still left three points of contact, butfurther reduction to 55° 30 as shown by l
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