Pitch in Compression Springs - By Team Shama Spring

Pitch is the distance from the center of one coil to the center of the next adjacent coil, measured parallel to the spring axis when the spring is at its free (uncompressed) length.

Let me create an illustrated diagram to show this concept clearly:

Key Definitions Pitch in Compression Springs:

Pitch (p) = The axial distance between corresponding points on adjacent coils, typically measured from center to center

Important Relationships:

1. Free Length Formula: L₀ = p × (n - 1) + d

   • Where: L₀ = free length, n = total coils, d = wire diameter

2. Pitch vs. Solid Height: When compressed to solid height, coils touch and pitch = wire diameter (d)

3. Active vs. Inactive Coils: End coils (usually ground flat) don't contribute to spring action, so pitch calculations use active coils

Practical Significance:

• Uniform pitch: Most springs have equal spacing between all coils

• Variable pitch: Some springs use different pitch values along the length for progressive spring rates

• Pitch angle: The helix angle of the coil, related to pitch and mean coil diameter

The pitch determines how much the spring can compress and affects its overall working characteristics!

Detailed Breakdown of Pitch in Compression Springs:

Calculation Steps:

Given:

• Wire diameter (d) = 5 mm

• Free length (L₀) = 100 mm

• Number of coils (n) = 7

Formula:

p = (L₀ - d) / (n - 1)

Calculation:

p = (100 - 5) / (7 - 1)
p = 95 / 6
p = 15.83 mm

Why subtract wire diameter?

The formula accounts for the fact that the top and bottom end coils (which are typically ground flat) take up space equal to approximately one wire diameter at each end.

Why (n - 1)?

With 7 coils, there are only 6 pitch intervals between them (the spaces between coils). Think of it like fence posts - 7 posts create 6 gaps between them.

Visual Verification:

• 6 pitch intervals × 15.83 mm = 95 mm

• Plus one wire diameter = 95 + 5 = 100 mm ✓

The illustration shows all 7 coils with the pitch clearly marked as the center-to-center distance between adjacent active coils!

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