Rack Information

What is Rack

A rack is a straight bar with gear teeth. It can convert rotational motion into linear motion, or vice versa, converting linear motion into rotational motion. It is widely used in various mechanical equipment, such as CNC machines, lifting mechanisms, and sliding doors.

History of Rack

The rack, as a special case of parallel shaft gears, was first recorded in the "Wubei Zhi" written by Mao Yuanyi during the Ming Dynasty in China, which described a gear rack transmission device. The bronze gear (rack) unearthed in Shanxi is the oldest gear found to date. In 1869, the world's first cog railway (Mount Washington Cog Railway) using gear rack was built. In 1885, the world's first "modern" rack and pinion steering system was first applied to the German "Benz" car. After the 1880s, with the emergence of special machines and tools based on the principle of generating gear cutting, the tools for gear (rack) processing became more complete. After the 1950s, racks were widely used in fields such as automated identification and mechanical equipment with high requirements for precision and load, as well as in large-scale mechanical equipment with heavy loads.

Purpose of Rack

The rack is mainly used for linear motion transmission, for example, converting rotational motion into linear motion. It is commonly used in equipment that requires linear motion, such as CNC machines, lifting mechanisms, and sliding doors.

Principle of Rack

The working principle of the gear rack is to convert the rotational motion of the gear into the reciprocating linear motion of the rack, or vice versa, converting the reciprocating linear motion of the rack into the rotational motion of the gear. The gear rack mechanism is composed of gears and racks. The tooth profile of the rack is a straight line, not an involute (for the tooth surface, it is a plane), which is equivalent to a cylindrical gear with an infinitely large pitch circle radius.

Features of Rack

• Linear tooth profile: The tooth profile of the rack is a straight line, so all points on the tooth profile have the same pressure angle, which is equal to the inclination angle of the tooth profile. This angle is called the tooth shape angle, and the standard value is 20°.
• Same pitch and modulus: The pitch and modulus are the same on any straight line parallel to the tooth top line.
• Division line as the reference line: The straight line that is parallel to the tooth top line and has the same tooth thickness as the tooth groove width is called the division line (middle line), which is the reference line for calculating the size of the rack.

Types of Rack

• Straight rack: The tooth grooves are distributed in a straight line, suitable for occasions that require linear motion, such as CNC machines and elevators.
• Helical rack: The tooth grooves are arranged diagonally, which can ensure smooth transmission and improve transmission efficiency. In some cases, it can also reduce noise.
• Curved rack: The tooth grooves are in an arc shape, suitable for occasions that require large stroke and heavy load, such as machine tools and heavy machinery.

Precautions for using Rack

• Installation environment: The installation of the rack should be carried out in a dust-free and dry environment to avoid the influence of dust and water on its accuracy.
• Installation base surface: Attention should be paid to the chamfer design on the back and bottom outer edges of the rack. During installation, it is necessary to ensure that the installation base surface of the rack is flat and clean.
• Side clearance adjustment: The standard rack is designed with a fixed side clearance. During assembly, just assemble according to the assembly distance and keep the assembly distance unchanged.

Things to consider when purchasing Rack

• Load capacity: Choose the appropriate gear rack modulus and material according to the load requirements of the equipment. The larger the modulus, the stronger the load capacity, but the cost will also increase accordingly.
• Accuracy grade: Choose the appropriate gear rack accuracy grade according to the accuracy requirements of the equipment. High-precision gear racks are suitable for occasions with high transmission accuracy requirements, such as CNC machines and precision machinery.
• Motion form and speed: Choose the appropriate gear rack type according to the motion form and speed requirements of the equipment. For linear motion, a straight tooth rack can be selected, and for rotational motion, a cylindrical gear can be chosen. At the same time, consider the speed range of the gear rack to ensure the stability and reliability of the transmission system.