Constant Force Springs

John Evans’ Sons is an international leader in constant force spring design and manufacturing. This includes spring assemblies, pusher springs (shelf pushers or variable force), constant tension springs, clock springs and various other constant force products.

Custom design, in-house tooling and precision manufacturing as well as a wide and varied stock spring selection, combined with our commitment to quality and on-time delivery, are our strongest selling points.

Our constant force springs and assemblies can eliminate costly and complicated motors, decreasing your device size and cost. These types of springs provide:

  • Smooth, even, uniform load through entire length or travel (deflection)
  • Strong force yield within small spaces
  • Extensive linear range
  • Small package size
  • Ability to easily mount to existing hardware

Design Considerations for Constant Force Springs

There are many design factors that will affect the time and cost needed to manufacture your spring. Therefore, it’s important to work with a manufacturer like John Evans’ Sons that has the knowledge needed in the design phase.

  • Mounting Methods: There are several mounting methods. Your application will determine which mounting method is best for your spring’s design.
  • Material: Material will certainly affect the design and project cost. High temperatures or corrosive environments will also affect the life of a spring and the required material.
  • Diameter and Load: Length, material width, thickness, and coil diameter affect the spring’s load. Increased loads can be obtained by using two or more constant force springs interwound, in tandem, or in other configurations.

All of these, plus other technical considerations, need to be discussed and specified prior to creating prototypes. Our design engineering team can help ensure calculations and configurations are exact in the design phase.

Our springs are most often used in the following industries and applications:3-d drawing of a constant force spring.

Not sure if constant force springs can provide the right action for your product? Contact John Evans' Sons for more information.

Spring Selection Chart

(material: T301 SS, Calculations shown are at 1.0” width, interpolate for other spring material widths)
Material Thickness2,500 cycles
Coiled Dia.Load (lbs.)
0.0020.151.3
0.0030.222
0.0040.32.6
0.0050.363.3
0.0060.444
0.0080.595.2
0.010.736.6
0.0120.878
0.0141.029.3
0.0161.1610.6
0.0181.3111.9
0.021.4613.2
0.0221.6114.5
0.0251.8116.5
0.0282.0418.5
0.0322.2620.5
Material Thickness10,000 cycles
Coiled Dia.Load (lbs.)
0.0020.171
0.0030.251.5
0.0040.342
0.0050.432.5
0.0060.513
0.0080.694
0.010.865
0.0121.036
0.0141.27
0.0161.378
0.0181.549
0.021.7110
0.0221.8911
0.0252.1412.5
0.0282.414
0.0322.6515.5
Material Thickness20,000 cycles
Coiled Dia.Load (lbs.)
0.0020.220.65
0.0030.321
0.0040.441.3
0.0050.551.6
0.0060.652
0.0080.872.6
0.011.083.3
0.0121.34
0.0141.524.6
0.0161.735.3
0.0181.965.9
0.022.186.6
0.0222.377.2
0.0252.728.2
0.0283.049.5
0.0323.3610.2
Material Thickness75,000 cycles
Coiled Dia.Load (lbs.)
0.0020.330.32
0.0030.480.5
0.0040.650.65
0.0050.810.8
0.0060.951
0.0081.281.3
0.011.591.6
0.0121.912
0.0142.222.3
0.0162.532.7
0.0182.853
0.023.23.3
0.0223.483.6
0.02544.1
0.0284.484.6
0.0324.945.1
Material Thickness150,000 cycles
Coiled Dia.Load (lbs.)
0.0020.440.17
0.0030.660.26
0.0040.890.35
0.0051.110.44
0.0061.330.52
0.0081.780.7
0.012.220.87
0.0122.671.04
0.0143.071.2
0.0163.61.4
0.01841.56
0.024.441.74
0.0224.891.91
0.0255.552.18
0.0286.232.44
0.0326.92.7
Constant force spring variables & formula.

Selection Charts for the Ideal Constant Force Spring

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
Available from our distributor, Stock Drive Products. Tel: 516-328-3300
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

CLICK for a larger selection chart, LIVE data & ordering links!

STOCK Constant Force Spring Selection Chart

Order small quantities (click chart shown above).

Large Multi-Leaf (interwound), Highly Specialized End Detail & Sub-Miniature Constant Force Spring Examples

Constant Force Springs
Constant Force Springs
Constant Force Springs

Download .pdf

"Stock" Constant Force Springs

"Stock" Constant Force Spring Selection Chart w/links

Download .pdf

Constant Force Balance Springs

Info Sheet

Download .pdf

Point Of Purchase

"Pusher" Variable Force Spring

Download .pdf

Window Balance Springs

1/2" Constant Force Window Balance Selection Guide

Download .pdf

Window Balance Springs

3/4" Constant Force Window Balance Selection Guide

Got A Question? Consult our Experts.

Our experts offer a depth of expertise to assist you with all parts of the process. We are ready to answer your questions in a timely manner and will help you define what you need. We produce custom springs for all purposes, and we are here to work with you on any of your customization needs.

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