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Thursday, 28 November 2013

Gear-Tooth Forms

Gear-Tooth Forms Points : Gear-Tooth Forms In order for mating gears of the same module (or diametric pitch) to mesh with a smooth, quiet, rolling action, they must have the proper gear-tooth form. Two basic forms (or curves) for gear teeth are used one with an involutes curve, a second that is a composite of the Involutes curve and cycloidal curves. The shape of a cycloidal curve. Mating gears with either of these forms will roll together smoothly and quietly without interference when operated at the prescribed pressure angle. Several systems of gear-tooth form have been standardized, and cad) system is designed to operate at a specified pressure angle, usually at 14 1/2°, 20’, or 25°.

Gears with the involute curve tooth design are the most widely used. The teeth of gears with the composite tooth form are very similar to those of the involute form, except for the design of b sic rack teeth. This rack has an involute curve in the area of the pitch line, but it is modified slightly with cycloidal curve in areas above and below the pitch line. The modification prevents interference between mating gears that have a small number of teeth. Gears with the composite tooth form normally are produced on milling machines, with form type rotary milling cutters. The use of this tooth form largely is limited to the production of gears in small job shops, maintenance shops, and shops where small numbers of gears are produced. This form of gear also may be produced by hobbing or with other gear-generating machines.

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