Shaft Size Calculator
Calculate minimum shaft diameter for various loading conditions and design requirements
Calculate Shaft Diameter
Select the loading condition for shaft design
Power transmitted by the shaft
Rotational speed in revolutions per minute
Twisting moment acting on the shaft
Maximum allowable shear stress (Steel: 42 MPa)
Shaft Size Results
Hollow Shaft Design
Ratio between inner and outer diameter (0 < k < 1)
Formula used: d³ = 16T / (π × τ)
Design Analysis
Example Calculation
Power Transmission Shaft
Power: 20 kW
Speed: 200 RPM
Material: Mild Steel (τ = 42 MPa)
Design Basis: Torsion only
Step-by-Step Calculation
1. Calculate Torque: T = 60P/(2πN) = (60 × 20,000)/(2π × 200) = 955 N⋅m
2. Apply Torsion Formula: T = πτd³/16
3. Solve for diameter: d³ = 16T/(πτ) = (16 × 955)/(π × 42×10⁶)
4. d³ = 1.157×10⁻⁴ m³
Result: d = 48.7 mm minimum diameter
Common Material Properties
Mild Steel
Alloy Steel
Cast Iron
Combined Load Factors
Gradually Applied Load
Minor Shocks
Heavy Shocks
Design Tips
Always use the larger diameter from combined stress calculations
Consider deflection limits and critical speed for long shafts
Hollow shafts reduce weight while maintaining strength
Allow for keyway stress concentration when applicable
Select standard shaft sizes available commercially
Understanding Shaft Design and Sizing
What is Shaft Design?
Shaft design involves calculating the minimum diameter required for a rotating member to safely transmit torque and withstand various loads. The design must ensure stresses remain within allowable limits while meeting performance requirements.
Types of Loading
- •Torsion: Twisting moment from power transmission
- •Bending: Transverse loads from gears, pulleys, and shaft weight
- •Combined: Simultaneous torsion and bending loads
- •Fluctuating: Variable loads with shock and fatigue factors
Design Formulas
Torsion Only
d³ = 16T / (π × τ)
For pure twisting loads
Bending Only
d³ = 32M / (π × σ)
For pure bending loads
Combined Loading
Te = √(M² + T²)
Equivalent twisting moment
Solid vs Hollow Shafts
Hollow shafts provide better strength-to-weight ratio and material savings. The k ratio (inner/outer diameter) typically ranges from 0.3 to 0.8 for optimal design.
Safety Factors
Combined shock and fatigue factors account for variable loading conditions. Higher factors are used for sudden loads and heavy machinery applications.
Torsional Rigidity
Critical for applications like camshafts where angular twist must be limited. Typical limit is 0.25° per meter of shaft length.