1. What is Critical Speed Scuff Calculator?

Definition: This calculator determines the critical speed at which a rotating shaft begins to experience scuffing or excessive vibration based on gravity and shaft deflection.

Purpose: It helps mechanical engineers and technicians prevent shaft failure by identifying dangerous rotational speeds.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( N_c \) — Critical speed (revolutions per minute)
• \( g \) — Acceleration due to gravity (9.81 m/s²)
• \( \delta \) — Static deflection of the shaft (meters)
• \( \pi \) — Mathematical constant pi (approximately 3.1416)

Explanation: The formula calculates the rotational speed where the shaft's natural frequency matches the rotational frequency, causing resonance.

3. Importance of Critical Speed Calculation

Details: Knowing the critical speed helps prevent mechanical failures, excessive vibration, and potential safety hazards in rotating equipment.

4. Using the Calculator

Tips: Enter the gravity value (default 9.81 m/s²) and the shaft deflection in meters. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What happens at critical speed?
A: At critical speed, the rotating shaft experiences resonance, leading to excessive vibration that can cause damage or failure.

Q2: How is deflection measured?
A: Deflection is typically measured as the static displacement of the shaft midpoint under its own weight.

Q3: Should operating speed be above or below critical speed?
A: Operating speed should be either well below (30% less) or well above (30% more) the critical speed to avoid resonance.

Q4: Does this apply to all shaft types?
A: This calculation is most accurate for uniform, simply supported shafts. Complex shafts may require more advanced analysis.

Q5: What units should be used?
A: Use meters for deflection and m/s² for gravity to get RPM as the result.