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.
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.
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.
- Up to 25 mm steps of 0.5 mm
- 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.
The following stresses are induced in the shafts.
- Shear stresses due to the transmission of torque (due to torsional load).
- 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.
- Stresses due to combined torsional and bending loads.
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- 112 N/mm2 for shafts with allowance for keyways.
- 84 N/mm2 for shafts without allowance for keyways.
The maximum permissible (design) shear stresses may be taken as:
- 56 N/mm2 for shafts with allowance for keyways.
- 42 N/mm2 for shafts without allowance for keyways.