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Coil Springs Mean Diameter

Compression Springs Compression Springs

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Hint: The closer your min and max inputs are, the more accurate your results will be!

Outside Diameter
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Inside Diameter
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Free Length
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Wire Diameter
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Total Coils
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Rate
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Material Type
Max. Load
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Max. Deflection
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Solid Height
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*Required Field
Extension Springs Extension Springs

Input results shown will be +/- 10% from middle value
Hint: The closer your min and max inputs are, the more accurate your results will be!

Outside Diameter
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Length Inside Hook
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Wire Diameter
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Max. Load
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Max. Deflection
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Initial Tension
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Rate
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Material Type
*Required Field
Torsion Springs Torsion Springs

Input results shown will be +/- 10% from middle value
Hint: The closer your min and max inputs are, the more accurate your results will be!

Outside Diameter
to
Inside Diameter
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Total Coils
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Free Position
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Wire Diameter
to
Body Length
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Max. Torque
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Max. Deflection
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Rate
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Leg Length
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Material Type
*Required Field
Conical Springs Conical Springs

Input results shown will be +/- 10% from middle value
Hint: The closer your min and max inputs are, the more accurate your results will be!

Small Outside Diameter
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Large Outside Diameter
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Free Length
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Rate
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Total Coils
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Solid Height
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Wire Diameter
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Material Type
*Required Field

 

Definition: Coil spring specification that measures the diameter in between the spring’s outer and inner diameters.

 

Mean diameter is used to calculate several formulas which are necessary to your design such as index and wire length for manufacturing reasons, or spring rate to know your spring’s force and working loads.

 

Coil spring mean diameter can be measured many ways. It is like your spring’s outer and inner diameters except, instead of measuring from the outside of the coil or the inside of the coil, you will measure from in between these spring dimensions; from the center of the coil’s wire. The formula and diagram to calculate coil spring mean diameter are the following.

 

To calculate mean diameter you must simply either subtract one wire diameter from the outer diameter or add one wire diameter to the inner diameter.

 

Coil Spring Mean Diameter Formula

 

Mean Diameter = Outer Diameter – Wire Diameter
Mean Diameter = Inner DIameter + Wire Diameter

Example

You have a spring with a wire diameter of 0.035 inches, an outer diameter of 0.500 inches, and an inner diameter of 0.430 inches.

MD = OD – WD
MD = 0.500 – 0.035
MD = 0.465

MD = ID + WD
MD = 0.430 + 0.035
MD = 0.465

Formula Diagram

 

Calculate Mean Diameter from Outer DiameterCalculate Mean Diameter from Outer Diameter
Calculate Mean Diameter from Inner DiameterCalculate Mean Diameter from Inner Diameter

Coil Spring Index Formula

 

To calculate spring index you must divide the mean diameter by the wire diameter as the formula shows below.


I = MD ÷ WD

Example

You have two springs. Spring A has a mean diameter of 2.750" inches and a wire diameter of 0.250 inches. Spring B has a mean diameter of 2.500 inches and a wire diameter of 0.500 inches.

 

Spring A

I = MD ÷ WD
I = 2.75 ÷ 0.25
I = 11 to 1

Spring B

I = MD ÷ WD
I = 2.5 ÷ 0.5 I = 5 to 1

Formula Diagram

 

Coil Spring Index CalculationCoil Spring Index Calculation

Coil Spring Wire Length

To calculate your coil spring’s wire length using coil spring mean diameter, you must multiply the mean diameter by pi and multiply the product by the total number of coils.


Wire Length = Mean Diameter x Pi x Total Coils

Example

You have a mean diameter of 0.465 inches and 10 total coils.


WL = 3.14 MD(TC)
I = 3.14 x 0.465 x 10
I = 14.601 inches
 
 

Coil Spring Rate Formula

 

To calculate your coil spring’s rate there are several factors to consider besides your coil spring mean diameter. The formula along with symbol nomenclature is shown below.


D = D outer – d
G = E ÷ 2(1 + V)
k = Gd^4 ÷ (8D^3 x na)

Nomenclature
  • d = Wire Diameter
  • D outer = Outer Diameter
  • D = Mean Diameter
  • E = Young's Modulus of Material
  • G = Shear Modulus of Material
  • k = Spring Rate
  • na = Active Coils
  • V = Poison's Ration of Material

Formula Diagram

 

Coil Spring Rate CalculationCoil Spring Rate Calculation

 

Spring Rate Calculator

 

Coil Spring Calculator - Spring CreatorCoil Spring Calculator - Spring Creator

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