To avoid interference, pressure angles are commonly related to the worm lead angle as indicated in Table 15.1. Lead angle λ, Lead L, and worm pitch diameter d 1 have the following relationship in connection with the screw threads.ġ3. The face width of the gear should not exceed half the worm outside diameter.
Strength considerations seldom permit a shell worm to have a pitch diameter less than d 1 = 2.4p + 1.1ġ1. Shell worms are bored to slip over the shaft and are driven by splines, key, or pin. Integral worms cut directly on the shaft can, of course, have a smaller diameter than that of shell worms, which are made separately. For maximum power transmitting capacity, the pitch diameter of the worm should normally be related to the shaft center distance by the following equationĨ. A worm of any pitch diameter can be made with any number of threads and any axial pitch.
#Worm gear design calculation pdf plus
Worm gears usually have at least 24 teeth, and the number of gear teeth plus worm threads should be more than 40: Z 1 + Z 2 > 40Ħ. This means that the velocity ratio of a worm gear set is determined by the ratio of gear teeth to worm threads it is not equal to the ratio of gear and worm diameters.ĥ. The pitch diameter of a worm is not a function of its number of threads, Z 1.
When the angle is 90 between the nonintersecting shafts, the worm lead angle is equal to the gear helix angle. As with a spur or helical gear, the pitch diameter of a worm gear is related to its circular pitch and number of teeth Z by the formulaĢ. Enveloping the gear gives a greater area of contact but requires extremely precise mounting. The geometry of a worm gear is similar to that of a helical gear, except that the teeth are curved to envelop the worm. Rotation of the worm simulates a linearly advancing involute rack, Fig.15.3 b. The geometry of a worm is similar to that of a power screw. 15.3 Nomenclature of a single enveloping worm gearĪ. (b) (a) Fig.15.1 (a) Single enveloping worm gear, (b) Double enveloping worm gear.įig.15.2 The cut section of a worm gearbox with fins and fan for coolingįig. Contents 15.1 Worm gears –an introduction 15.2 Worm gears - geometry and nomenclature 15.3 Worm gears- tooth force analysis 15.4 Worm gears-bending stress analysis 15.5 Worm gears-permissible bending stress 15.6 Worm gears- contact stress analysis 15.7 Worm gears- permissible contact stress 15.8 Worm gears -Thermal analysisġ5.1 INTRODUCTION Worm gears are used for transmitting power between two non-parallel, non-intersecting shafts.