Full definition
Cylindrical rotating element that transmits torque from a power source to driven components such as pulleys, gears, sprockets, and couplings. Typical materials: AISI 1045 medium-carbon steel (general industrial, yield ~530 MPa) or AISI 4140 chrome-moly alloy (heavy duty, yield ~655 MPa, through-hardened or case-hardened). Shaft diameter is selected based on torque (τ = T·c/J), critical speed (must operate below 70% of first critical), and allowable deflection (max 0.01"/ft for gears, 0.005"/ft for precision). Keyways per DIN 6885 or ANSI B17.1. Surface finish at seal and bearing locations: Ra 0.2-0.8 μm. Per ASME B106.1M for design. Oversizing wastes material; undersizing risks fatigue failure.