Shaft Torsional Stress

WHAT THIS SCREEN ANSWERS

A shaft that transmits torque must be checked for more than its outside diameter. Torsional stress rises with torque and falls sharply with diameter. The cubic diameter relationship is why a small diameter change can have a large effect on nominal stress. This screen makes that first relationship visible before a shaft is judged from a motor torque rating alone.

Enter torque at the shaft, actual shaft diameter, and an allowable shear stress supported by the material condition and design context. MechPlane calculates nominal maximum torsional shear stress for a solid round section and shows the proportion of the entered limit. The allowable is deliberately user-entered because material grade alone does not establish a valid design limit.

Real shafts commonly contain keyways, shoulders, splines, cross holes, transitions, and mounted components. They also see bending, fatigue cycles, deflection, bearing reactions, corrosion, surface condition, and manufacturing variation. Those features can govern long before a clean solid-shaft torsion equation. A simple ratio is useful for screening, not for certifying a shaft.

Use this page to compare early shaft diameters and identify whether torsion warrants a fuller layout review. Continue to combined stress, deflection, critical speed, keyway, and bearing checks as appropriate. Confirm material properties, stress concentrations, fatigue criteria, manufacturing requirements, and any applicable standards with qualified engineering review before release.