Gear Overview

Gears: 5 Minute Tutorial

Gears are incredible mechanical components. Gears have existed for thousands of years; the earliest gears were had wooden teeth with pin or wedge shapes. However the shape of modern gears has evolved to reduce friction, noise, and wear. Most spur gear tooth shapes are based upon involute profiles, which minimize frictional losses. Some resoruces include:

Overview of gears in Wikipedia includes many neat figures and animations
For reliable operation, an in-depth understanding of gears design considerations should be performed, and the Boston Gear Company provides a good technical reference.
See experiments done on Lasercamm cut gears by Owen Richey showing that the involute profile really does make a difference!


Terminology of Spur Gear geometry. From http://www.sdp-si.com	Animation showing continuous contact force in an involute tooth profile. From www.engineeringexpert.net

A key parameter is the pitch circle, which indicates where the teeth should mesh, and is used in calculating the Center Distance. The Pressure Angle indicates the angle at which the contact force between gear teeth occur. Although for rough force estimates a zero pressure angle is sometimes used. To make your own gears on the Lasercamm, you can use the files below which were generated from the Autodesk Inventor Design Accelerator (using a pressure angle of 20 degrees). The larger the pitch number, the smaller the gear tooth. Each "Pitch Set" below contains a number of different diameter. gears to choose from.

Advantages of Large Teeth Size (small pitch number)

Stronger teeth which are less likely to break
Requires less precision to mesh

Advantages of Small Teeth Size (large pitch number)

Small gears are possible, since one typically needs at least 8 teeth per gear.
Less backlash (the amount of play in the gears before they engage when changing direction of rotation)

32 pitch
24 pitch (works but not updated with latest Inventor files)
20 pitch
16 pitch (“typical” MAE3 gears)
12 pitch (“typical” MAE3 gears)
10 pitch (“typical” MAE3 gears)
8 pitch
6 pitch
Racks of various sizes (used for rack and pinion systems)

A Few Design Considerations with Gears:

Proper meshing of gears requires high precision. The centers of the gears should be mounted so that the pitch circle (shown in the figure above) meet in a tangential fashion.

Making Your Own Gear Shapes

If you do not find the gear size you want in the files above you can make your own size gears in Inventor

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