Gears come in different shapes, sizes and types depending on their intended use. Some of the common type of gears include:
• Spur gears
• Helical gears
• Beveled gears
• Worm gears
• Planetary gears
Spur gears are probably the simplest form of gears with straight teeth that are parallel to the axis of rotation of the gear. Example of spur gears are shown in the figure below.
Figure 1. Spur gears used on a lathe
Helical gears are typically used in applications where smoother and quieter operation is needed; this often occurs for applications with higher rotational speeds. The teeth have a spiral or helical shape that increases the contact area between two gears. This reduces the stress on the teeth and allows better meshing between gears.
Figure 2. Examples of helical gears
Beveled gears allow two shafts to meet at an angle, usually 90°, but other angles are also possible. The gears are conical or have a “bevel” as the name suggests. Bevel gears can have straight teeth, similar to spur gears, or they can be helical (known as spiral bevel gears). Figure 3 shows a set of spiral bevel gears from an angle grinder.
Figure 3. A set of spiral bevel gears from an angle grinder
Worm gears consist of a screw and a spur or helical gear (see Figure 4 below). As the screw turns, it drives the spur or helical gear. This type of gear is used in instances where two shafts do not intersect. The advantage of a worm gear is that it has a high gear ratio to dramatically reduce speed while allowing for better transmission of power.
Figure 4. Illustration of a worm gear
Planetary gears consist of several gears that look similar to a “planetary” system. There is a central gear (sun gear) with adjacent gears spinning around it (planet gears); these gears are surrounded by an internal gear that contains the entire system. Planetary gears are typically used in vehicle automatic transmissions; depending on which of the gears are held stationary, various gear ratios can be achieved. Various examples of planetary gears can be found on the web.