Spur Gears
The simplest and the easiest type of gear is the spur gear. The spur gear transmits power and motion between parallel shafts and it is widely used in all common transmission applications. The teeth of gear is parallel to the axis of shaft. The following fig shows a pair of spur gear.
Spur Gear Terminology
The below diagram shows the various terminologies used in spur gear.
Force Analysis of Spur gears
Spur gears produce no thrust forces, however it has two force components the radial component(Fr) and the tangential component(Ft). Gears has to be fasten firmly with stepped shafts, or collars, to prevent shifting toward the shaft. Keyways are generally used in fastening gears to a shaft, and they should be secured by applying drilled holes for set screws, or applying flats to the shaft, in case of fastening only with set screws.
Bending Strength of Spur Gear
Allowable bending strength of a gear is defined as the allowable tangential force at the pitch circle based on the mutually
allowable root stress of two meshing gears under load.
Surface durability of Spur Gear
The surface durability of a gear is defined as the allowable tangential force at the pitch circle, which permits the force to be
transmitted safely without incurring surface failure.
Design of Spur Gear