Language:

What Is Gear Rack?

Oct 16,2023

What is Gear Rack?

A gear rack is a type of gear on which gear teeth are cut on one face of a bar. The bar can be square, round or rectangular in cross section and the teeth can be either parallel to the base or set at an angle. They are a simple and common type of element in mechanical drive systems and are always paired with a pinion.

Gear racks convert power and motion from rotary motion into linear motion. For straight tooth gear racks, the mating pinion must be the same pitch, and the same pressure angle. When the gear rack teeth are helical, the pitch, the pressure angle, and the helix angle of both the pinion and the gear rack must be the same; however, the direction of the helix angle of each component must be opposite.

The teeth of a gear rack are cut using a rack milling machine. The milling head machines a section of rack and then indexes to the adjacent section until the rack is completed. The maximum length of a rack is only limited by the length of the milling machine. Gear racks can be produced from various materials, including steel, brass, bronze, or plastic, and depending on the application, they can be hardened based on the requirements for strength and durability.

The geometry of a gear rack is defined by several parameters. In a theoretical sense, a gear rack is just a spur gear with an infinite pitch diameter. The calculations vary depending on whether the teeth are produced in the normal system or the transverse system. Table 1 details the calculations for a gear rack and a profile shifted pinion. This gear tooth modification factor is not typically applied but is sometimes used to manipulate the center distance of a gear rack and pinion. In most applications, this value is set to zero for the pinion.

The first value needed to produce a gear rack is the pitch. In the metric system, this is known as the module. As the value of the module increases, the size of the gear tooth increases. In the English standard system, the pitch of a helical gear is known as the diametral pitch (DP). It represents the number of teeth that are found on a gear with a one-inch reference diameter.