Referring to Figure 9-4, for a lead angle ɣ, measured on the pitch cylinder, each rotation of the worm makes the thread advance one lead. Thus, a one-thread worm is equivalent to a one-tooth gear and two-threads equivalent to
To the number of teeth in a gear of a screw type gear mesh. The number of threads in the worm is equivalent Generally, the mesh has a 90° shaft angle. Thus, a worm is characterized by theĩ.1.3 Pitch Diameters, Lead and Lead AngleĬylindrical worms may be considered cylindrical type gears with screw threads. For slightly smallerĪngles, there can be two, three or even more threads. The worm can be considered resembling a helical gear with a high helix angle.įor extremely high helix angles, there is one continuous tooth or thread. A high pressure angle is favored and in some applications values as high as 25° and 30° are used.
The standard values apply to the central section of the mesh. Worm tooth dimensions, such as addendum, dedendum, pressure angle, etc., follow the same standards as those for spur and helical gears.
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