Herringbone Gears

Herringbone gears use teeth with two opposing helices to transmit power and motion between parallel axes. The mirrored halves of the gear face have teeth that resemble an arrow head or the letter V. Some products have a machined center groove. Most herringbone gears are used with heavy machinery and large-diameter shafts. They apply equal force and friction to both gears and cancel the resulting thrust forces. Materials of construction for a herringbone gear include aluminum, brass, bronze, cast iron, carbon steel, hardened steel, and stainless steel. Herringbone gears are also made of plastics such as acetal, nylon, and polycarbonate. Gears that feature metal teeth with plastic inserts combine the strength and fit properties of a metal hub with the benefits of plastic teeth, which include quieter running and greater fit tolerances.

Specifications for herringbone gears include units of measure, number of teeth, pitch diameter, face width, tooth width, outside diameter, and pressure angle. English gears are measured in units such as inches (in). Metric gears are measured in units such as centimeters (cm). The number of teeth and the pitch diameter determine the pitch of the gear. There are two types of pitch: circular and diametrical. Circular pitch (CP) is a direct measurement of the distance from one tooth center to the adjacent tooth center. Diametral pitch (DP) is the ratio of the number of teeth to the pitch diameter. As a rule, a higher DP indicates finer tooth spacing. Pressure angle is the angle between the line of force between meshing teeth and the tangent to the pitch circle at the point of mesh. Like double helical gears, herringbone gears must have the same pressure angle and outer diameter (OD) in order to mesh. Additional parameters for herringbone gears include design life, noise and heat generation, power transmission requirements, and the use of corrosive materials.

Like worm gears, herringbone gears can be mounted on a hub or shaft. A hub is a cylindrical projection on one or both sides of gear, often for the provision of a screw or other shaft-attachment mechanism. Most hubless gears are attached with a press-fit, adhesive, or internal keyway. Shaft mounting choices for herringbone gears also include set screws, hub clamping screws, split-style, and simple bore. Applications for herringbone gears include power transmission and speed reduction.

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