Downloads (.pdf format):
1/2" width Window Spring
Selection Guide
3/4" width Window Spring
Selection Guide
Constant Force
Balance Springs Tear Sheet
For Point of Purchase:
Pusher Variable Force Springs
Constant Force Springs
The constant force spring can be used to counterbalance items such as windows (known in the window industry as coil balance springs), doors, display racks and trays. It can also be used as a return or retracting mechanism wherein the constant force spring will provide a smooth, even, uniform load through its entire length or travel (deflection). Travel (extension, deflection) is limited only by the length of material in the spring. Load is a function of material width, thickness and coil diameter. Increased loads can be obtained by using two or more constant force springs interwound or in tandem or in other configurations.
Section 1
Stock Spring Selection Chart
The constant force springs listed below are available in small quantities from our stocking distributor, Stock Drive Products (SDP), or in larger quantities direct from our factory.
For engineers and designers envolved in prototype development, who may require quick delivery of small quantities, click on part numbers below to be directed to a page within the Stock Drive Components website.
NOTE: For production quantities, Simply determine the proper part number from specifications in chart below and contact John Evans' Sales Department directly.
Downloads (.pdf format):
Production Qty. -Stock Constant Force Springs
JES Selection Guide
Small Qty. -Stock Constant Force Springs
SDP Selection Guide
Stock Constant Force Spring
Selection Chart
(Material: 301 stainless steel)
| Part Number |
Load |
Max Work Deflection | Band Length | Fatigue Life (cycles) | Width |
Free I. D. |
Thickness |
|---|---|---|---|---|---|---|---|
| A 3X50-SL04D16 | 0.23 | 12" |
16" |
20,000 |
0.25" | 0.516 | 0.004 |
| A 3X50-SK04D15 | 0.32 | 12" |
15" |
13,000 |
0.25" | 0.438 | 0.004 |
| A 3X50-SL05E17 | 0.36 | 12" |
17" |
20,000 |
0.3125" | 0.656 | 0.005 |
| A 3X50-SH03C10 | 0.37 | 8" |
10" |
2,500 |
0.1875" | 0.219 | 0.003 |
| A 3X50-SK04E15 | 0.4 | 12" |
15" |
13,000 |
0.3125" | 0.438 | 0.004 |
| A 3X50-SL05F30 | 0.43 | 25" |
30" |
20,000 |
0.375" | 1.0 | 0.005 |
| A 3X50-SH04C14 | 0.49 | 12" |
14" |
2,500 |
0.1875" | 0.297 | 0.004 |
| A 3X50-SK05E16 | 0.49 | 12" |
16" |
13,000 |
0.3125" | 0.563 | 0.005 |
| A 3X50-SL06F24 | 0.52 | 18" |
24" |
20,000 |
0.375" | 0.781 | 0.006 |
| A 3X50-SH04D14 | 0.66 | 12" |
14" |
2,500 |
0.25" | 0.297 | 0.004 |
| A 3X50-SL06G24 | 0.7 | 18" |
24" |
20,000 |
0.5" | 0.781 | 0.006 |
| A 3X50-SK06F23 | 0.71 | 18" |
23" |
13,000 |
0.375" | 0.672 | 0.006 |
| A 3X50-SH04E14 | 0.83 | 12" |
14" |
2,500 |
0.3125" | 0.297 | 0.004 |
| A 3X50-SL08G31 | 0.93 | 24" |
31" |
20,000 |
0.5" | 1.047 | 0.008 |
| A 3X50-SK06G23 | 0.95 | 18" |
23" |
13,000 |
0.5" | 0.672 | 0.006 |
| A 3X50-SH05E15 | 1.03 | 12" |
15" |
2,500 |
0.3125" | 0.359 | 0.005 |
| A 3X50-SK08G30 | 1.26 | 24" |
30" |
13,000 |
0.5" | 0.875 | 0.008 |
| A 3X50-SL10J33 | 1.46 | 24" |
33" |
20,000 |
0.625" | 1.328 | 0.010 |
| A 3X50-SH06F21 | 1.48 | 18" |
21" |
2,500 |
0.375" | 0.438 | 0.006 |
| A 3X50-SK08J30 | 1.58 | 24" |
30" |
13,000 |
0.625" | 0.875 | 0.008 |
| A 3X50-SH06G21 | 1.97 | 18" |
21" |
2,500 |
0.5" | 0.438 | 0.006 |
| A 3X50-SK10J32 | 1.98 | 24" |
32" |
13,000 |
0.625" | 1.109 | 0.010 |
| A 3X50-SL12K42 | 2.09 | 30" |
42" |
20,000 |
0.75" | 1.578 | 0.012 |
| A 3X50-SK10K32 | 2.37 | 24" |
32" |
13,000 |
0.75" | 1.109 | 0.010 |
| A 3X50-SH08G28 | 2.63 | 24" |
28" |
2,500 |
0.5" | 0.578 | 0.008 |
| A 3X50-SL12P42 | 2.8 | 30" |
42" |
20,000 |
1" | 1.578 | 0.012 |
| A 3X50-SK12K40 | 2.84 | 30" |
40" |
13,000 |
0.75" | 1.344 | 0.012 |
| A 3X50-SH08J28 | 3.29 | 24" |
28" |
2,500 |
0.625" | 0.578 | 0.008 |
| A 3X50-SL15P46 | 3.5 | 30" |
46" |
20,000 |
1" | 1.984 | 0.015 |
| A 3X50-SK12P40 | 3.79 | 30" |
40" |
13,000 |
1" | 1.344 | 0.012 |
| A 3X50-SH10J29 | 4.12 | 24" |
29" |
2,500 |
0.625" | 0.734 | 0.010 |
| A 3X50-SL15R46 | 4.37 | 30" |
46" |
20,000 |
1.25" | 1.984 | 0.015 |
| A 3X50-SK15P42 | 4.74 | 30" |
42" |
13,000 |
1.0" | 1.672 | 0.015 |
| A 3X50-SH10K29 | 4.95 | 24" |
29" |
2,500 |
0.75" | 0.734 | 0.010 |
| A 3X50-SK18P47 | 5.69 | 32" |
47" |
13,000 |
1.0" | 2.0 | 0.018 |
| A 3X50-SL20R54 | 5.83 | 36" |
54" |
20,000 |
1.25" | 2.625 | 0.020 |
| A 3X50-SH12K36 | 5.94 | 30" |
36" |
2,500 |
0.75" | 0.875 | 0.012 |
| A 3X50-SL20S54 | 6.99 | 36" |
54" |
20,000 |
1.5" | 2.625 | 0.020 |
| A 3X50-SH12P36 | 7.92 | 30" |
36" |
2,500 |
1.0" | 0.875 | 0.012 |
| A 3X50-SL25S59 | 8.74 | 36" |
59" |
20,000 |
1.5" | 3.297 | 0.025 |
| A 3X50-SK20S52 | 9.48 | 36" |
52" |
13,000 |
1.5" | 2.219 | 0.020 |
| A 3X50-SH16P38 | 10.6 | 30" |
38" |
2,500 |
1.0" | 1.156 | 0.016 |
| A 3X50-SL25U59 | 11.7 | 36" |
59" |
20,000 |
2.0" | 3.297 | 0.025 |
| A 3X50-SK25S57 | 11.9 | 36" |
57" |
13,000 |
1.5" | 2.781 | 0.020 |
| A 3X50-SL31U69 | 14.4 | 42" |
69" |
20,000 |
2.0" | 4.078 | 0.031 |
| A 3X50-SK25U57 | 15.8 | 36" |
57" |
13,000 |
2.0" | 2.781 | 0.025 |
| A 3X50-SH20R47 | 16.5 | 36" |
47" |
2,500 |
1.25" | 1.469 | 0.020 |
| A 3X50-SK31U68 | 19.6 | 42" |
68" |
13,000 |
2.0" | 3.438 | 0.031 |
| A 3X50-SH20S47 | 19.8 | 36" |
47" |
2,500 |
1.5" | 1.469 | 0.020 |
| A 3X50-SH25S48 | 24.8 | 36" |
48" |
2,500 |
1.5" | 1.828 | 0.025 |
| A 3X50-SH25U48 | 33 | 36" |
48" |
2,500 |
2.0" | 1.828 | 0.025 |
| A 3X50-SH31U58 | 40.9 | 42" |
58" |
2,500 |
2.0" | 2.266 | 0.031 |
Section 2
Technical Information & Dia. vs. Load Chart
Load values for stainless steel have been tabulated in the accompanying table for various cycles (fatigue life) and material thicknesses, using a basic design width of one inch. The load is directly proportional to the material width in a constant force spring, but is not directly proportional to material thickness. These springs can also be made of tempered carbon spring steel, but greater forces are obtained from stainless steel in this type of spring. Springs made of stainless steel also offer superior performance in harsh environments.
Coiled Diameters and Load
(lbs. per 1" width of stainless steel)
| Material Thickness | 2,500 cycles | 10,000 cycles | 20,000 cycles | 75,000 cycles | 150,000 cycles | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| Coiled Dia. | Load | Coiled Dia. | Load | Coiled Dia. | Load | Coiled Dia. | Load | Coiled Dia. | Load | |
| 0.002 | 0.15 | 1.3 | 0.17 | 1.0 | 0.22 | 0.65 | 0.33 | 0.32 | 0.44 | 0.17 |
| 0.003 | 0.22 | 2.0 | 0.25 | 1.5 | 0.32 | 1.0 | 0.48 | 0.50 | 0.66 | 0.26 |
| 0.004 | 0.30 | 2.6 | 0.34 | 2.0 | 0.44 | 1.3 | 0.65 | 0.65 | 0.89 | 0.35 |
| 0.005 | 0.36 | 3.3 | 0.43 | 2.5 | 0.55 | 1.6 | 0.81 | 0.80 | 1.11 | 0.44 |
| 0.006 | 0.44 | 4.0 | 0.51 | 3.0 | 0.65 | 2.0 | 0.95 | 1.00 | 1.33 | 0.52 |
| 0.008 | 0.59 | 5.2 | 0.69 | 4.0 | 0.87 | 2.6 | 1.28 | 1.30 | 1.78 | 0.70 |
| 0.010 | 0.73 | 6.6 | 0.86 | 5.0 | 1.08 | 3.3 | 1.59 | 1.60 | 2.22 | 0.87 |
| 0.012 | 0.87 | 8.0 | 1.03 | 6.0 | 1.30 | 4.0 | 1.91 | 2.00 | 2.67 | 1.04 |
| 0.014 | 1.02 | 9.3 | 1.20 | 7.0 | 1.52 | 4.6 | 2.22 | 2.30 | 3.07 | 1.20 |
| 0.016 | 1.16 | 10.6 | 1.37 | 8.0 | 1.73 | 5.3 | 2.53 | 2.70 | 3.60 | 1.40 |
| 0.018 | 1.31 | 11.9 | 1.54 | 9.0 | 1.96 | 5.9 | 2.85 | 3.00 | 4.00 | 1.56 |
| 0.020 | 1.46 | 13.2 | 1.71 | 10.0 | 2.18 | 6.6 | 3.20 | 3.30 | 4.44 | 1.74 |
| 0.022 | 1.61 | 14.5 | 1.89 | 11.0 | 2.37 | 7.2 | 3.48 | 3.60 | 4.89 | 1.91 |
| 0.025 | 1.81 | 16.5 | 2.14 | 12.5 | 2.72 | 8.2 | 4.00 | 4.10 | 5.55 | 2.18 |
| 0.028 | 2.04 | 18.5 | 2.40 | 14.0 | 3.04 | 9.5 | 4.48 | 4.60 | 6.23 | 2.44 |
| 0.031 | 2.26 | 20.5 | 2.65 | 15.5 | 3.36 | 10.2 | 4.94 | 5.10 | 6.90 | 2.70 |
Various end details are possible, and tooling for many are already available. The constant force spring can be installed in several ways. The spring is often mounted on a bushing or a spool for tension applications. Fastening the spring to the bushing, or guiding the spring with flanges, is only required when deflection is extreme. We can mount the spring(s) for you on bushings or spools that either you or we provide.
The constant force spring can be installed in various ways. The spring is often mounted on a bushing or a spool for tension applications. Fastening the spring to the bushing, or guiding the spring with flanges, is only required when deflection is extreme. John Evans' can mount the spring(s) for you on bushings or spools that either you or we provide.
For samples, questions,
or design assistance, e-mail
or call our Sales Department.
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