Shaft (mechanical engineering)

In mechanical engineering, a shaft is a rotating machine element, usually circular in cross section, which is used to transmit power from one part to another, or from a machine which produces power to a machine which absorbs power.

Types
They are mainly classified into two types.
 * Transmission shafts are used to transmit power between the source and the machine absorbing power; e.g. counter shafts and line shafts.
 * Machine shafts are the integral part of the machine itself; e.g. crankshaft.
 * Axle shaft.
 * Spindle shaft.

Materials
The material used for ordinary shafts is mild steel. When high strength is required, an alloy steel such as nickel, nickel-chromium or chromium-vanadium steel is used. Shafts are generally formed by hot rolling and finished to size by cold drawing or turning and grinding.

Standard sizes
Source:

Machine shafts

 * Up to 25 mm steps of 0.5 mm

Transmission shafts

 * 25 mm to 60 mm with 5 mm steps
 * 60 mm to 110 mm with 10 mm steps
 * 110 mm to 140 mm with 15 mm steps
 * 140 mm to 500 mm with 20 mm steps

The standard lengths of the shafts are 5 m, 6 m and 7 m.

Usually 1m to 5m is used.

Stresses
The following stresses are induced in the shafts.
 * 1) Shear stresses due to the transmission of torque (due to torsional load).
 * 2) Bending stresses (tensile or compressive) due to the forces acting upon the machine elements like gears and pulleys as well as the self weight of the shaft.
 * 3) Stresses due to combined torsional and bending loads.