Bevel and Miter Gears

Gears are mechanical devices that transmit mechanical power and motion. They are widely used for speed reduction or increase, torque multiplication, resolution, and accuracy enhancement for positioning systems. Bevel and miter gears transmit power and motion between nonparallel axes.  Bevel gears are designed to transmit motion between intersecting axes, which are usually at right angles. Miter gears are bevel gears specifically made for a 1:1 ratio at 90°.

Bevel and miter gears may have spiral teeth, in which case a set must contain opposite-hand gears to mesh. Gears mate or mesh via teeth with very specific geometry.  Pitch is a measure of tooth spacing and is expressed in several ways: 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 number of teeth to the pitch diameter (in inches) of a gear; a higher DP therefore indicates finer tooth spacing.   Module (mod or M) is used for metric gears and is the ratio of pitch diameter (in mm) to the number of teeth; a higher module therefore indicates coarser tooth spacing.  Pressure angle is another specification of tooth form and is the angle of tooth drive action, i.e. the angle between the line of force between meshing teeth and the tangent to the pitch circle at the point of mesh. Gears must have the same pitch and pressure angle in order to mesh. In addition, spiral bevel gears must be of opposite hand specification to mesh.  Other important specifications to consider include the gear center, bore diameter, and shaft diameter.  The gear center can be a center bore or an integral shaft.  The bore diameter is the diameter of center bore for gears with a bore.  The shaft diameter is the diameter of shaft for gears with integral shaft.

Materials of construction for bevel and miter gears can be metal or plastic.  Gears are made from a wide variety of materials with many different properties. Factors such as design life, power transmission requirements, noise and heat generation, and presence of corrosive elements contribute to optimization of gear material. Consult with a gear manufacturer on a specific application for the best material.  Metal choices include aluminum, brass, bronze, cast iron, steel, hardened steel, and stainless steel.  Plastic choices include acetal, Delrin, nylon, and polycarbonate.  Ground teeth provide smoother, higher-precision tooth form.  Combination bevel and miter gears can have plastic teeth with metal inserts.  Bevel and miter 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. Hubless gears are typically attached via press fit, adhesive, or internal keyway.  Shaft mounting choices include keyway, set screws, hub claming screws, split, and simple bore. 

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