What is a spur gears?
Spur gear is a relatively simple type of gear and belongs to the category of cylindrical gears. Its teeth are parallel to the axis, making it widely used, easy to manufacture, and commonly seen in various applications.
Characteristics of Spur Gears
Spur gears have involute tooth profiles, engaging one tooth at a time. The involute form means that spur gears generate only radial forces (no axial forces), but the method of tooth engagement can result in high stress and noise. Therefore, although spur gears can be used at almost any speed, they are typically employed in low-speed applications. The involute tooth profile of spur gears is a circular involute, meaning that when two gears mesh, they contact at a single point along the involute.
As the gears rotate, this point moves along the tooth surface, and the line of action （known as the line of action） tangentially intersects the two base circles. Thus, gears adhere to the fundamental law of gear transmission, which stipulates that the ratio of angular velocities must remain constant throughout the entire meshing process.
What Materials are Commonly Used for Spur Gears?
Spur gears can be made from metals （such as steel or brass） or plastics （such as nylon or polycarbonate）. Gears made of plastic produce less noise but may have reduced strength and load-bearing capacity. Gears made of steel can undergo heat treatment processes, enhancing wear resistance.
How are Spur Gears Manufactured?
There are several common methods for manufacturing spur gears. First, hobbling involves using a tool with gear-shaped cutters to continuously move up and down to cut the shape of the gear on the cylindrical surface.
Second, milling involves using a milling cutter mounted on a milling machine with a groove shape matching the tooth groove of the gear. After milling one gear, the workpiece rotates a distance equal to one tooth, and the process is repeated to form spur gears.
Third, gear shaping utilizes a hob to cut multiple gears simultaneously. As the hob rotates one full turn, it rapidly cuts multiple gears on the workpiece, ensuring efficiency.
Calculations for Spur Gears
Addendum = Addendum Coefficient * Module
Dedendum = （Addendum Coefficient + Dedendum Coefficient）*Module
Whole Depth = Addendum + Dedendum
Pitch Circle Diameter = Module * Number of Teeth
Base Circle Diameter = Pitch Circle Diameter *cos20（for standard gears）
Tip Circle Diameter = Pitch Circle Diameter + 2* Dedendum
Root Circle Diameter = Pitch Circle Diameter -2* Dedendum
Pitch = π * Module
Tooth Thickness = Tooth Saw / 2
Tooth Gap Width = Tooth Thickness
Standard Center Distance = Sum of Pitch Circle Diameters / 2
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