What is a Miter Gear?

A miter gear is part of the bevel gear family designed to work in pairs and with both gears having identical dimensions and number of teeth. Miter gears are designed for applications where the rotational speed of the input and output drives remains constant but the direction changes. Generally the difference in drive/output orientation in miter gear sets is 90°, although sets are available which produce a selection of angular deviations. Miter gears are available in either spiral or straight toothed configurations. Spiral miter gears are better suited to high speed applications such as power tool and machine drives. Straight cut miter gears are suitable for low speed applications such as door opener mechanisms and hand tools.

Miter gear sets are used in machinery designs requiring changes in drive direction while maintaining drive speeds. These criteria are achieved by employing a set of cone shaped gears of identical size, profile, and tooth number. This design allows the gears to be positioned in an opposed orientation while maintaining a constant speed relationship between the two drives. In the majority of cases, the miter gear turns the output drive at right angles to the input. Gear sets can, however, be designed to effect almost any directional deviation.

These gears fall into two basic categories: spiral or straight cut. This terminology refers to the angle that the teeth of the gear cut at in relation to the face or cone angle. Spiral cut gears are more appropriate for high speed applications because the curve of the teeth allows for gradual engagement. This reduces the amount of “clashing” when the teeth of the two gears engage and make the gear train stronger and quieter. This type of gear is commonly used in high speed applications such as lawn trimmers where the motor and drive shaft are orientated at right angles to one another.

A straight cut miter gear is more suitable for slow speed applications such as hand operated door openers and hand tools. In these applications, the straight cut gears' shortcomings are less noticeable, and the reduced cost of production makes their use attractive. Miter gear materials are dictated by their intended end use with hard faced, high carbon steel appropriate for high load and high speed applications. Nylon and various injection molding resins are used for gears which don't work as fast or as hard. The close relationship between individual gears means that both gears in a set should ideally be replaced together even if only one is worn or damaged.