Worm gears gear ratio

The worm thread is a major factor in worm ratios and is an important feature in worm design. The speed-reduction ratio is equal to the total number of worm-gear teeth divided by the number of worm threads. 

So that reliable test results could be obtained, five test repetitions of four different worm gears described in the previous chapter were carried out, starting always from the same point and with identical rotation direction. On this way, there will be four rolling tests for each gear size tested, assuring if there is any influence on the result derived from the variation of the transmission ratio. 

One revolution of the worm advances the gear by as many teeth as there are threads on the worm. Therefore, the ratio of transmission is equal to the number of teeth on the gear, divided by the number of threads on the worm, without regard to the pitch. 

Benefiting from the high gear ratio between the DC motor and the lead screw and the negligible moment of inertia of worm, worm gear, and coupling elements, the 3-DOF model in Fig. 9.8 is approximated by the 1-DOF model shown in Fig. 9.19. 

Number of threads in worm. The minimum number of teeth in the gear and the reduction ratio will determine the number of threads for the worm. Generally 1 to 10 threads are used. 

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