Why use fixed positions for balancing?

Many rotating components like fans, impellers, and turbines have fixed blade or bolt positions where correction weights can be attached. Unlike a smooth drum where weights can be placed at any angle, these rotors limit placement to discrete positions. The blade correction method mathematically decomposes the required correction into two masses at the nearest available positions.

How does the calculator find the adjacent positions?

The positions are evenly spaced at 360/N degrees. The calculator finds the two positions that bracket the required correction angle. For example, with 6 blades (60° spacing) and a correction at 40°, the adjacent positions are blade 1 (0°) and blade 2 (60°).

What if the correction falls exactly on a blade position?

If the correction angle coincides exactly with a blade position, all the correction mass goes to that single position and the other adjacent position gets zero mass. The calculator handles this automatically.

How do I balance a fan with fixed blades?

Steps: 1) Measure the initial vibration. 2) Calculate the required correction mass and angle (using influence coefficient or trial weight methods). 3) Use this calculator to split the correction into two adjacent blade positions. 4) Attach the calculated masses to the specified blades. 5) Verify with a final vibration measurement.

Should I add mass or remove mass from blades?

Both approaches work. Adding mass (welding, bolting, or clipping weights) is placed at the calculated angle. Removing mass (grinding, drilling) is done 180° opposite to the calculated angle. For blade tips, adding small weights or grinding material are both common. The choice depends on the blade construction and operating conditions.

Free Engineering Tool — #012

Blade Correction Calculator

Decompose a correction mass at any angle into two masses at adjacent fixed blade or bolt positions. For fans, impellers, and turbines with evenly spaced positions.

Fixed Positions Fan & Impeller 4–20 Blades

Number of Positions (blades/bolts)

Correction Mass (g)

Correction Angle (degrees)

Correction Radius (mm, same for all)

Quick presets

Results

Mass at Position A

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Position A

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Mass at Position B

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Position B

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Unbalance Check

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Angular Spacing

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Fixed-Position Decomposition

When correction weights can only be placed at fixed angular positions (blades, bolts), the required correction at angle θ is decomposed into two adjacent positions θ_a and θ_b using moment balance:

Position Layout

Positions are evenly spaced at 360° / N intervals, numbered 1 to N starting from 0°:

N Positions	Spacing	Max Error
4	90°	45°
6	60°	30°
8	45°	22.5°
12	30°	15°
20	18°	9°

ℹ️ Note: More positions means smaller angular spacing and better approximation. With 12+ positions, the correction is very close to continuous placement.

Practical Example

Example — 6 Blades, 15g at 40°

Given: 6 blades (60° spacing), correction = 15g at 40°

Adjacent positions: Blade 1 at 0°, Blade 2 at 60°

m_a = 15 × sin(60° − 40°) / sin(60° − 0°) = 15 × sin(20°) / sin(60°) = 15 × 0.342 / 0.866 = 5.92 g at 0°

m_b = 15 × sin(40° − 0°) / sin(60° − 0°) = 15 × sin(40°) / sin(60°) = 15 × 0.643 / 0.866 = 11.13 g at 60°

⚠️ Note: The sum of m_a + m_b will generally be slightly more than the original correction mass. This is normal — the excess compensates for the angular offset. The vector sum equals the original correction exactly.

Blade Correction Calculator | Fixed Positions | Fan & Impeller

Published by admin on February 15, 2026 February 15, 2026

Results

Fixed-Position Decomposition

Position Layout

Practical Example