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Secrets of the Trade
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Spring makers posses a vast amount of knowledge. In this section they can share that knowledge with their fellow spring makers around the world. We encourage all great spring makers to post a few trade secrets in a specific category. Each spring maker that posts a secret of the trade will get full credit for their submission and their trade secret will be posted for everyone to see. Enjoy!

"Spring makers unite and collaborate with each other for the better good of the Spring world !!"
FORMULAS TO DETERMINE SPRING RATE
Use formulas below along with the formula index and torsional modulus of elasticity

Compression Spring Terminology
Extension Spring Terminology
Torsion Spring Terminology
Formulas for Index
R Rate per inch
P Load in pounds
S Stress (uncorrected)
H Solid height
G Torsional modulus of elasticity
p Pitch
M Moment or torque, in-lb
E Modulus of elasticity
n Active coils
N Total coils
D Mean diameter of coil
d Diameter of wire
π Pi, 3.14
L Free length
T Revolutions of spring
Sk Corrected stress
Torsional Modulus of Elasticity Data
Steel 11.5 x 106
Stainless Steel 10 x 106
Chrome Vanadium 11.5 x 106
Chrome Silicon 11.5 x 106
Phosphor Bronze 6.25 x 106
Brass 5.5 x 106
Formula key
Wire diameter (d) d = 8PD
        piS3
Active Coils (n) n = Gd4
       8RD2
Uncorrected Stress S = 8PD psi
 piD3
Spring rate (R) R = P2 - P1
     L2 - L1
Type of Ends
Closed & Ground Open Open Ground Closed
Pitch p = L-d
       n		 p =  L 
       N		 p = L-3d
       n		 p = L-2d
       n
Solid Height (H) H = d(N + 1) H = dN H = d(N + 1) H = dN
Active coils (n) n = N n = N - 1 n = N - 2 n = N - 2
Total Coils (N) N = L-d
       p		 N =  L 
       p		 N = L-3D + 2
 p		 N = L-2d + 3
 p
Free Length (L) L = pN = d) L = pN L = pN + 3d L = pN + 2d
"K" Factor