CORE PRINCIPLES
What to establish first
- Resolve the transmitted load and its duty cycle.
- Compare stress, stiffness and fatigue limits with an appropriate allowable value.
- Account for geometry changes such as shoulders, keys and fillets.
Machine Design
Shafts, joints, component sizing and mechanical design checks.
MODULE OVERVIEW
Machine Design in practical engineering work.
Machine design connects load paths, material behaviour, geometry, manufacture and service conditions. A component calculation is one checkpoint in an iterative design process, not a complete design release.
DESIGN CONCEPTS
Terms worth checking
- Strength and stiffness
- Stress concentration
- Design factor
Common applications: Power-transmission shafts · Couplings and keys · Machine frames and rotating assemblies
KEY RELATIONSHIP
Solid shaft torsion
T = πτd³ / 16
- T — torque, N·mm
- τ — selected allowable shear stress, MPa
- d — solid-shaft diameter, mm
Diameter has a cubic effect on torsional capacity, so a small sizing change can materially change stress.
WORKED EXAMPLE
Known values → substitution → interpretation
- Known values
- T = 98,793 N·mm; τ = 37.5 MPa
- Method
- d = ∛(16T/(πτ))
- Interpretation
- The torsion-only diameter is about 23.7 mm; a real shaft still needs bending, keyway, fatigue and standard-size checks.
KEY DESIGN CHECKS
Confirm the conditions behind the number
- Define the governing load case, duty cycle and required design life before using a simplified relation.
- Use compatible units and material data for the actual condition, temperature and manufacturing state.
- Compare the result with strength, stiffness, fatigue, safety, serviceability and applicable-code requirements.
COMMON ENGINEERING MISTAKES
Keep the model within its scope
- Applying solid shaft torsion outside the assumptions shown on this page.
- Using a nominal condition while a peak, alternating, transient or environmental case governs the design.
- Treating a calculated value as a final component selection without checking interfaces, tolerances and the current governing standard.
AVAILABLE CALCULATORS
Select a calculator
RELATED RESOURCE
Review the shaft-torsion formula
See variables, units, stated assumptions and the linked calculator.
Open related resource →REFERENCES & LIMITATIONS
Use this content as a transparent starting point
ReferenceJ. E. Shigley et al., Mechanical Engineering Design, sections on stress analysis and machine elements.ScopeRelationships are presented for the assumptions stated on this page and linked tool.Design reviewCheck material condition, loads, environment and the applicable current code.SafetyResults are educational/preliminary and do not certify safety or compliance.
RELATED ENGINEERING