Are worm gears reversible?
Unlike with ordinary gear trains, the direction of transmission (input shaft vs output shaft) is not reversible when using large reduction ratios. This is due to the greater friction involved between the worm and worm wheel, and is especially prevalent when a single-start (one spiral) worm is used.
How does a worm gear move?
A worm gear is a gear consisting of a shaft with a spiral thread that engages with and drives a toothed wheel. It changes the rotational movement by 90 degrees, and the plane of movement also changes due to the position of the worm on the worm wheel (or simply “the wheel”).
Are worm gears self locking?
Self-locking means that the gear cannot drive the worm. In other words, back driving is not possible. In theory, as long as the coefficient of friction between the gear and the worm is larger than the tangent of the worm’s lead angle, the worm gear is considered self-locking and will not back drive.
What is the angle of worm thread?
90°
Generally, the mesh has a 90° shaft angle. The number of threads in the worm is equivalent to the number of teeth in a gear of a screw type gear mesh. Thus, a one-thread worm is equivalent to a one-tooth gear; and two-threads equivalent to two-teeth, etc.
How does a gear hobbing machine work?
Gear-hobbing machines use a rotating, multiple-tooth cutting tool called a hob for generating teeth on spur gears, worm gears, helical gears, splines, and sprockets. More gears are cut by hobbing than by other methods because the hobbing cutter cuts continuously and produces accurate gears at…
When should I use worm gear?
This makes worm gears suitable for use where noise should be minimized, such as in elevators. The primary benefit of worm gears is their ability to provide high reduction ratios and correspondingly high torque multiplication. They can also be used as speed reducers in low- to medium-speed applications.
Can you drive a worm gear backwards?
Theoretically, “self-locking” worm gear speed reducers cannot be driven backwards. When worm gearing is self-locking or irreversible, this means that the worm gear cannot drive the worm.
Why are worm gears self-locking?
In theory, a worm gear is self-locking when the static friction angle is larger than the helix angle of the worm. The static friction angle is described as the angle where the load above will start to move.
How does the whirling process for improved worm gears work?
This method completely eliminates the need for thread grinding. Cylindrical grinding of the bearing journals can also be eliminated by turning the soft blanks to finished tolerances and surface roughness prior to whirling the worm section.
What kind of machine is used to cut worm gears?
The cutting process of the worm gear tooth is generally completed by a hobbing machine, mainly including two methods of hobbing and flying cutter cutting. When manufacturing precision worm gears, it is possible to perform finishing such as shaving, squeegee or grinding after hobbing or cutting.
Which is the best way to harden a worm shaft?
Computer files store the control and position parameters to be recalled for each worm part number. In many cases, the best way to harden a worm shaft is to scan the worm section. In this process, the induction coil–a ring-shaped copper element–has a length much shorter than the worm-face width.
How is induction heating used in worm gears?
Induction heating can be programmed to harden only certain areas of a worm shaft. For example, the bearing journals can remain soft and only the worm section hardened. The induction hardening process is very repeatable and achieves a high hardness quality with consistent results.