1. What is the Shaft Size Calculation?

The shaft size calculation determines the minimum diameter required for a shaft to safely transmit torque while withstanding bending moments, based on allowable material stresses.

2. How Does the Calculator Work?

The calculator uses the combined stress formula:

Where:

• \( d \) — Shaft diameter (m)
• \( T \) — Applied torque (N·m)
• \( \tau \) — Allowable shear stress (Pa)
• \( M \) — Bending moment (N·m)
• \( \sigma \) — Allowable normal stress (Pa)

Explanation: The equation combines both torsional and bending stresses to determine the minimum shaft diameter that won't exceed material limits.

3. Importance of Shaft Size Calculation

Details: Proper shaft sizing is critical for mechanical system reliability. Undersized shafts may fail, while oversized shafts are unnecessarily heavy and expensive.

4. Using the Calculator

Tips: Enter torque in N·m, stresses in Pa, and bending moment in N·m. All values must be positive (except bending moment can be zero for pure torsion).

5. Frequently Asked Questions (FAQ)

Q1: What if there's no bending moment?
A: If M = 0, the equation simplifies to the pure torsion formula: \( d = \sqrt[3]{\frac{16T}{\pi\tau}} \)

Q2: How do I determine allowable stresses?
A: Allowable stresses are typically 25-50% of the material's yield strength, depending on safety factors.

Q3: Does this account for fatigue?
A: No, this is for static loading. Fatigue analysis requires additional considerations.

Q4: What about keyways or other stress concentrators?
A: Stress concentration factors should be applied separately to the calculated stresses.

Q5: Is this valid for hollow shafts?
A: No, this formula is for solid circular shafts. Hollow shafts require different calculations.