How Gears Work

Gears are used in many mechanical devices to provide speed reduction in motorized equipment. A small, rapidly-turning motor can provide enough power for some devices, but not enough torque.

02/01/2001


Gears are used in many mechanical devices to provide speed reduction in motorized equipment. A small, rapidly-turning motor can provide enough power for some devices, but not enough torque. An electric screwdriver has a large gear reduction because it needs torque to turn screws, but the motor produces a small amount of torque at high speed. With gear reduction, the output speed is reduced while the torque is increased.

Gears can also change rotational direction. Automobile differentials use bevel gears to turn the power from the drive shaft 90 deg and send it to the wheels.

The distance from the center of the gear to the point of contact determines gear ratio. If one gear is twice the diameter of the other, the ratio is 2:1.

Spur gears

Spur gears are the most common type. They have straight teeth and are mounted on parallel shafts. A sequence of spur gears can be used to create very large gear reductions.

Spur gears can be noisy. Each time a tooth engages a tooth on the other gear, they collide, making noise and increasing the stress on the teeth.

Helical gears

Helical gear teeth are cut at an angle to the face of the gear. More than one tooth on a helical gear system is always engaged. Contact starts at one end of a tooth and gradually slides across the face as the gears rotate.

This gradual engagement and multiple tooth contact make helical gears operate smoother and quieter than spur gears. Helical gears are usually mounted on parallel shafts, but if the gear tooth angles are correct, they can be mounted on perpendicular shafts, changing the rotation angle by 90 deg.

Because of the tooth angle, they create a thrust load on the gear when they mesh. Devices with helical gears have bearings that can support this thrust load.

Bevel gears

Bevel gears are useful when the direction of the rotation axis must be changed. They are typically mounted on shafts 90-deg apart, but can be designed to work at other angles.

Teeth on bevel gears can be straight or spiral. Straight bevel gear teeth have the same problem as straight spur gear teeth-as each tooth engages, it contacts the corresponding tooth all at once.

The solution to this problem is to curve the gear teeth. These spiral teeth engage just like helical gear teeth. Contact starts at one end of the gear and progressively slides across the whole tooth.

On straight and spiral bevel gears, the shafts must be mounted in the same plane so that the gear centers are aligned.

Worm gears

Worm gears are used when large gear reductions are necessary. Worm gears can have reductions of 20:1; some exceed 300:1.

Many worm gears have a unique property-the worm can easily turn the gear, but the gear cannot turn the worm. This difference is because the angle on the worm is so shallow that when the gear tries to spin it, the friction between the gear and the worm holds the worm in place. This property is useful for conveyer systems because the locking feature can act as a brake for the conveyer when the motor is not turning.

Involute gear profile

Today, virtually all gears use a tooth profile called an involute. This specially curved profile maintains a constant ratio of rotational speed between the two gears. As the gears spin, the point of contact moves, but the tooth profile continually compensates for the movement.

Marshall Brain, founder and CEO of HowStuff Works.com, will be at the Association for Facilities Engineering (AFE) booth Monday and Tuesday (March 5-6) of National Manufacturing Week.





Top Plant
The Top Plant program honors outstanding manufacturing facilities in North America.
Product of the Year
The Product of the Year program recognizes products newly released in the manufacturing industries.
System Integrator of the Year
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
June 2018
2018 Lubrication Guide, Motor and maintenance management, Control system migration
May 2018
Electrical standards, robots and Lean manufacturing, and how an aluminum packaging plant is helping community growth.
April 2018
2017 Product of the Year winners, retrofitting a press, IMTS and Hannover Messe preview, natural refrigerants, testing steam traps
June 2018
Machine learning, produced water benefits, programming cavity pumps
April 2018
ROVs, rigs, and the real time; wellsite valve manifolds; AI on a chip; analytics use for pipelines
February 2018
Focus on power systems, process safety, electrical and power systems, edge computing in the oil & gas industry
Spring 2018
Burners for heat-treating furnaces, CHP, dryers, gas humidification, and more
April 2018
Implementing a DCS, stepper motors, intelligent motion control, remote monitoring of irrigation systems
February 2018
Setting internal automation standards

Annual Salary Survey

After two years of economic concerns, manufacturing leaders once again have homed in on the single biggest issue facing their operations:

It's the workers—or more specifically, the lack of workers.

The 2017 Plant Engineering Salary Survey looks at not just what plant managers make, but what they think. As they look across their plants today, plant managers say they don’t have the operational depth to take on the new technologies and new challenges of global manufacturing.

Read more: 2017 Salary Survey

The Maintenance and Reliability Coach's blog
Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
One Voice for Manufacturing
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Maintenance and Reliability Professionals Blog
The Society for Maintenance and Reliability Professionals an organization devoted...
Machine Safety
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
Research Analyst Blog
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Marshall on Maintenance
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
Lachance on CMMS
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
Electrical Safety Update
This digital report explains how plant engineers need to take greater care when it comes to electrical safety incidents on the plant floor.
Maintenance & Safety
The maintenance journey has been a long, slow trek for most manufacturers and has gone from preventive maintenance to predictive maintenance.
IIoT: Machines, Equipment, & Asset Management
Articles in this digital report highlight technologies that enable Industrial Internet of Things, IIoT-related products and strategies.
Randy Steele
Maintenance Manager; California Oils Corp.
Matthew J. Woo, PE, RCDD, LEED AP BD+C
Associate, Electrical Engineering; Wood Harbinger
Randy Oliver
Control Systems Engineer; Robert Bosch Corp.
Data Centers: Impacts of Climate and Cooling Technology
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
Safety First: Arc Flash 101
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
Critical Power: Hospital Electrical Systems
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me