Shaft Stress Calculator
Shaft stress checks usually split into torsional shear stress, bending stress and the combined stress at the critical section. Use the working shaft calculators to check stress, twist and required diameter from the loads on the shaft.
Torsional shaft stress
For a circular shaft in elastic torsion, maximum shear stress is at the outside surface. The torsion calculator evaluates the polar moment and angle of twist from the same inputs.
tau_max = T * r / J
Bending and combined stress
If a pulley, sprocket, gear or overhung load bends the shaft, combine torque and bending at the same section before choosing diameter.
tau_combined = sqrt((sigma_b / 2)^2 + tau_t^2)
Practical workflow
- Use overhung-load or bearing data to find torque and bending moment.
- Check torsional stress and twist for the actual shaft diameter.
- Use the shaft diameter calculator if the stress margin is too small.
- Apply stress concentration, fatigue and keyway factors outside this first-pass screen.
Frequently asked questions
Is shaft stress the same as shaft torsion?
Not always. Torsion gives shear stress from torque. Shaft stress may also include bending from pulleys, sprockets, gears, bearings, shoulders and keyways.
Which calculator should I start with?
Use the torsion calculator when diameter is known and torque is the main load. Use the shaft diameter calculator when you need the required solid shaft size from torque and bending.
Related pages
- Shaft torsion calculator - maximum torsional shear stress, twist and torque capacity.
- Shaft diameter calculator - required solid shaft diameter from torque, bending and allowable stress.
- Shaft deflection calculator - round shaft bending stress and beam deflection.
- Overhung load calculator - bearing reactions and bending loads from pulleys, sprockets or gears.
- Keyway dimension calculator - key and keyway sizes after the shaft stress screen.