Gears are one of the most commonly used mechanisms in systems that have moving parts. Mechanical gears, or cogs, are used to transfer torque or power from one part to another.
If you look inside of a clock, you’ll find gears controlling the movement and speed of the hands. Cars also use gears to transfer power from the engine to the wheels.
The general purpose of every gear is the same, but there are many different types of gears, each with pros and cons.
This article covers the various types of mechanical gears and what they’re used for.
To start, there are external gears, and internal gears. As you probably guessed, external gears have the gear teeth on the outside of the part, while internal gears have teeth on the inside.
Internal gears can be more efficient than external gears, but they come with limitations. Internal gears can only work with an external gear, and only spur and helical gears can be internal gears. Internal gears have a size advantage, because the two centers of the meshed gears can be closer together. They’re commonly used in applications where space is limited.
Another difference between internal and external gears is the way they spin while working together. When two external gears are working, they spin in opposite directions. While an internal and external gear work together, they spin in the same direction.
Spur gears are the simplest and most common type of gear. The teeth on spur gears line up parallel and transmit the power and torque to a parallel shaft. Spur gears are commonly used in vehicles, conveyor systems, speed reducers, and more.
The purpose of these gears is to change speed in a system. For example, a smaller spur gear is used with a larger gear to reduce speed. The smaller gear might spin 100 times, and spin the larger gear 1 time.
Spur gears are easy to manufacture, and they’re fairly efficient.
A rack and pinion is more of a system than gears. The pinion is the spur gear, and the rack is the toothed straight edge. This system uses a spur gear and a flat surface with matching gear teeth. Rather than transferring continual movement, a rack and pinion transfers rotational power into linear movement.
Rack and pinion systems are often used in a linear actuator, stairlifts, and steering systems.
Helical gears are very similar to spur gears. The difference is, the teeth on helical gears are cut at an angle, and the gears line up in opposite directions so the teeth mesh together.
Just like spur gears, these gears transfer power to a parallel shaft.
The advantage of helical gears is that there are multiple gear teeth in contact, and when the gear teeth come into contact, it’s more gradual. This offers two benefits:
There are also double helical gears that have two helical gears side by side to increase the contact area of the teeth.
Bevel gears are gears formed on a cone, rather than a cylinder. Instead of meshing parallel, bevel gears mesh together perpendicularly. This changes the direction of the movement, turning linear power into vertical power.
These gears are commonly used in a vehicle’s differential and rear axle assembly. Bevel gears are also common in the manufacturing industry, including lathes and drilling machines.
Most bevel gears are used at a 90°, but they can be used at various angles.
A worm gear consists of two differently shaped gears. One gear is shaped like a screw, and the other gear is similar to a spur gear. The worm gear meshes on top of the other gear and rotates to move the other gear. Like bevel gears, worm gears also transfer the power perpendicularly rather than parallel.
Worm gears have less friction and are typically quieter, but they are less efficient in terms of power transfer. Worm gears can produce significant reductions in speed in compact spaces, making them useful in many industrial applications.
There are many different ways to manufacture gears. The right manufacturing method depends largely on the size, material, and precision requirements of the gears.
Die casting is a common method used to manufacture gears, and gear blanks. Casting is a process where molten metal is poured into a metal die mold. Secondary machining processes can be used to add the gear teeth or improve the surface finish.
Casting is typically used for larger gears, and gears that don’t require high precision.
CNC milling is a common precision machining process. The raw material—usually a round metal bar stock—is held in place and a rotating cutting tool removes material to form the part.
CNC milling can be used to form any type of gear, use any material, and maintain tight tolerances.
Broaching is a precision machining process that uses a cutting tool called a broach to remove material and form a part. A custom broach is expensive, so broaching is used to manufacture high quantities of identical gears.
Broaching is most commonly used to cut internal gearing, and less common to cut angled gearing.
Gears are continuously in contact with other metals, and most gears are in high-fatigue work environments. The common materials used for gears are high-strength steels.
4000-grade Molybdenum steel alloys offer excellent strength, wear resistance, and heat resistance. This steel alloy is very common in the automotive industry.
86xx steel alloys are low-carbon alloy steels that offer good toughness and core strength. These alloys have better machinability compared to 4000-grade steels.
9310 is low-carbon steel similar to the other alloys. It has high core hardness and high fatigue strength. This alloy is commonly used for aircraft gears, but less suitable for high temperature applications.
Steel alloys are almost always heat treated after machining to increase the strength and durability of the parts.
Some softer alloys like brass and bronze are used for gears that require less strength and hardness. Because these alloys are softer, there’s less physical wear on the gears. Brass and bronze are also more resistant to corrosion compared to steel. The tradeoff is that the softer metals can’t handle high loads that steel can.
Spex offers a large selection of custom precision machined parts for whatever your project needs. We are an ISO 9001:2015 certified company, and our team specializes in precision machining and supply chain efficiency.
Our machined components are available in an array of different materials and finishes and are manufactured to meet all the highest quantity needs.
Reach out to our team to get a quote for custom precision fasteners.
Talk with one of our team members to get a quote for precision screws.
Phone: (585) 467-0520
85 Excel Drive
Rochester, NY 14621