1. What is a Shaft Critical Speed Calculator?

Definition: This calculator determines the critical speed of a rotating shaft, which is the speed at which the shaft becomes dynamically unstable.

Purpose: It helps mechanical engineers and designers ensure shafts operate below their critical speed to prevent resonance and failure.

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)

Explanation: The formula calculates the natural frequency of the shaft and converts it to RPM.

3. Importance of Critical Speed Calculation

Details: Operating near critical speed can cause excessive vibrations, leading to bearing failures, seal damage, and catastrophic shaft failure.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What causes shaft deflection?
A: Deflection results from the shaft's weight, attached components, and any radial loads acting on it.

Q2: How do I measure shaft deflection?
A: It can be calculated using beam deflection formulas or measured experimentally with dial indicators.

Q3: What safety margin should I use?
A: Typically, operate at least 20% below the critical speed or 20% above (if passing through quickly during startup/shutdown).

Q4: Does this account for multiple critical speeds?
A: No, this calculates only the first critical speed. Longer shafts may have higher-order critical speeds.

Q5: How does bearing type affect critical speed?
A: Bearing stiffness influences critical speed. More rigid bearings generally increase critical speed.