Crown Gears

Crown gear is another form of Bevel Gear. A crown Gear's teeth gets projected at exactly right angles to the plane of the wheel. Orientation wise the teeth of a crown gear exactly looks similar to the points on a crown. As already said Crown gears point of meeting is at right angles. That is if one gear is turning vertically (up and down), the other is turning horizontally (side to side). And they mesh with each other. Typically the Crown gears are used in conjunction with the pinion that is typically wide.

For a crown gear to mesh accurately, bevel gears are needed. Though Spur Gears are also seen meshing correctly with crown gears. The crown gear, which is a form of bevel gear that comes with a very large pitch angle is basically analogous to the rack of a spur gearing. However, due to practical applications, the tooth form does not assume the shape of a spherical involute. Infact the crown gear profile comes with a relatively simplified form.

Working of a Crown Gear
The working of the crown gears can be explained with the help of a tool called a chuck key. Let's see the diagram.

This particular instrument uses Crown Gears for tightening up a power drill bit. As the key is turned the “jaws” of the drill approaches each other for holding the bit in place. The Crown gears are placed this way so that there is no problem in tightening the bit.

Application of Crown Gears
One of the prime and valuable application of Crown gears lie in the Rotating Shaft Cam Switch. Rotating Shaft Cam switch is designed for controlling, cycling and sequencing of various machine operations. Let's see where exactly does the Crown Gear fits in the Rotating Shaft Cam Switch.

Two crown gears are used here. Actually the crown gears work here are essentially superimposed discs that has gear teeth. These teeth are upturned at the outer edges for easy angular adjustments. Each of the Crown gear as featured in the diagram has a slot. The degree of overlap of the slots can easily be adjusted. The pivoted wheel works by riding on the flat surface of the crown gear(inner one). This pivoted wheel then travels downward over the allotted common slotted region. The Calibrated dials that is attached to each of the crown gear is used for indicating switch on and off position via a window.