What’s a Gear Sector?

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Sector gears have teeth along only a short section of their circumference and are used in mechanisms with short, repetitive movements. They may have round, spur geared or linear driven elements and can have two outputs with different pitch values. They can be made from various materials.

A sector gear is a flat spur-type device that has teeth along only a short section of its circumference; the rest of the gear is smooth. These gears are used to drive other elements or are themselves driven in mechanisms that travel only through a short arc and not a full revolution. They are typically found in mechanisms that feature short, repetitive or reciprocating movements such as clocks, actuators and steering units. Segment gears may have only a short section of toothed surface or two opposing sections depending on the particular application. Depending on whether the output is radial or linear, this type of gear typically drives another bucket gear or a rack and pinion gear.

When close range low drive movement is required in a mechanism, a full range gear need not be used to initiate the operation as much of it will never run. Examples of these short cycle reciprocating operations include clock mechanisms, linear and radial actuators, and steering units on some vehicles. Often the range of motion in these applications can be close to a full 360°, but more often much less. The amount of motion, along with space constraints, transfer speeds, and torque requirements, will determine how many teeth are included in the sector gear and what its total radius will be.

The segmented gear driven elements may be round, spur geared or linear with flat rack, or may also be segmented gears themselves. Again, torque and transfer speed requirements play a role in determining the design, size, and tooth pitch, if any, of these driven gears. The sector gear is often also the driven gear as is the case with low speed and low torque sluice gates. A large semi-circular sector gear is attached to the gate and driven to raise or lower it by a smaller, full spur gear. Where large amounts of input torque or higher operating speeds are required, the configuration would be reversed.

One of the benefits of sector gear designs is their ability to have two outputs, often with different pitch values. These gears typically have two, or sometimes more, sets of sector gears along their edges which operate different parts of a reciprocating mechanism. Unlike a full range gear, individual sets of teeth can be cut at different pitches if speed differences are needed. Industry gears can be made from a variety of materials including ferrous metals, brass, and high impact plastics.

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