n14_springs
page 1 of 3
1) compression spring
squared and ground ends
d = 0.105 in
OD = 0.755 in
Lf = 2.25 in
Nt = 11.75
OK preferred wire size Table 14-2 Norton
assume A228 music wire
Na = Nt – 2 = 9.75
Fig. 14-9 Norton
D = OD – d = 0.650 in
C = D / d = 6.1905
Eq. 14-5
G = 11.7 x 106 psi
Table A-1 Norton
4
 11.7 x10 6 lbf 

d4 G
0.105 in 

 = 66.39 lbf/in

k=
8 D 3 N a 8 0.650 in 3 9.75 
in 2

Sut = A db = 266.3 ksi
A = 184649 psi
Sys = 0.45 Sut = 119.8 ksi
static
KS  1
b = -0.1625
Eq. 14.3 and Table 14-4 Norton
Table 14-8 Norton
0.5
= 1.0808
C
 MAX  K s
8FD
 S ys
 d3
3
 119.8x10 3 lbf 
0.105 in 

 = 77.55 lbf

Fy <
8 K s D 81.08080.650 in  
in 2

 d 3 S ys
Ls = d Nt = 1.234 in
shut length (fully compressed)
ys = Lf – Ls = 1.016 in
Fs = k ys = 67.45 lbf < Fy
 = 0.28 lbm/in3
Eq. 14.7 Norton
will not yield at shut length
Table A-1 Norton
w =  d 2 / 4   D  N t = 0.058 lbf
Eq 14.8b Norton
n14_springs
page 2 of 3
2) torsion spring garage door opener
rotating shaft crosses full width of door and has drums on each end
three bearings for shaft – left, center, right
steel cables connected to bottom of door (one on each side) are wound by drums to lift door
two torsion springs – one RH and one LH
springs fixed to front wall of garage above door at center
springs connected to rotating shaft by clamps with two set screws at rotating end
right torsion spring
clamp with set screws
center bearing and spring mounts
d = 0.242 in
OD = 2.484 in
Na = 143
not a preferred wire size Table 14-2 Norton
7 turns of preload when door closed
assume A229 oil tempered wire
D = OD – d = 2.242 in
C = D / d = 9.2645
E = 30 x 106 psi
kT =
Eq. 14-5
Table A-1 Norton
 30x10 6 lbf 
0.242 in 4
d4 E

 = 29.7 in.lbf/rev

10.8 D N a 10.8 2.242 in  143 
in 2

Eq. 14.29 Norton
 = 7 rev
M  k T  = 207.9 in.lbf = 17.32 ft.lbf
rDRUM = 2 in
radius of drum for cable to lift door
each turn of drum lifts door 2  rDRUM = 12.57 in
FCABLE = M / rDRUM = 104.0 lbf
force in cable to lift door (one cable on each side of door)
n14_springs
static at inside of coil
 i max  K bi
4C 2  C  1
= 1.0875
K bi 
4CC  1
32 M
= 162.5 ksi
 d3
Sut = A db = 190.4 ksi
Sy = 0.85 Sut = 161.8 ksi
N FS  S y /  i max = 0.9957
page 3 of 3
Eq. 14.32a Norton
Eq. 14.33a Norton
A = 146780 psi
b = -0.1833
Table 14-15 Norton
Eq. 14.3 and Table 14-4 Norton