Worm Gears Is a Device Consisting of a Threaded Shaft

Worm gears is a device consisting of a threaded shaft (worm) that mates with a gearwheel (worm wheel) so that rotary motion can be transferred between two shafts. These worm gear hobs can be hollow type or integral shank type depending upon strength constraints. Tangential, radial, topping or non-topping hobs and special reaming type finishing hobs are also available. Worm gears can be considered a species of helical gear, but its helix angle is usually somewhat large (close to 90 degrees) and its body is usually fairly long in the axial direction, and it is these attributes which give it its screw like qualities. Worm hobs are generally designed for plunge cutting. These hobs are a part of specific tools that match the worm shaft with sharpening allowance. Depending on finished gear accuracy specifications, worm gear hobs may be supplied either unground or ground, for roughing or finishing. Hobbing is a machining process for making gears, splines and sprockets on a hobbing machine, which is a special type of milling machine. The teeth or splines are progressively cut into the workpiece by a series of cuts made by a cutting tool called a hob. Compared to other gear forming processes it is relatively inexpensive but still quite accurate, thus it is used for a broad range of parts and quantities. The hob is the cutter used to cut the teeth into the workpiece. It is cylindrical in shape with helical cutting teeth. These teeth have grooves that run the length of the hob, which aid in cutting and chip removal. Worm gear, gear consisting of a shaft with screw thread (the worm) that meshes with a toothed wheel (the worm wheel); Changes the direction of the axis of rotary motion. The worm gear hobs are of different types according to the function they have to perfrom. They are discussed here in the following paragraph. Involute Gear Hob: They can generate gears with maximum precision. They are used when there would be no tooth finishing operation afterwards and there is need for better precision before tooth shaving operations. Sprocket Hobs: They are used for cutting roller chain sprockets. Can be produced in single or multi start. Serration Hob: They are designed for cutting the serrations as per job. These special hobs generate the correct tooth form at one level, so the accuracy has to be high. The specifications of such gear hobs can be changed according to the need of the client. Source: speedreducer.org