Constant Force Springs

John Evans’ Sons is an international leader in constant force spring design and manufacturing. Constant force springs are ideal for applications that require a smooth range of motion and consistent load. Included are constant force spring assemblies, constant and variable force pusher springs (shelf pushers), 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

Constant force springs are small and compact and can easily mount to existing hardware. Our constant force 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 our engineering team for more information on constant force springs and our other spring products and assemblies.

Design Considerations for Constant Force Springs

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

Depending on your product, you will likely need to be able to mount your constant force spring. There are several mounting methods, all of which will impact the design of your mechanical spring. We can help you determine which mounting method is best based on your application.

Material will certainly affect the design as well as cost. High temperatures or corrosive environments will also affect the life of a spring and the required material.

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. Again, working with a manufacturer that understands all of these factors can help ensure calculations and configurations are exact.

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 Springs

Category: , , , , , ,

Selection Charts for the Ideal Constant Force Spring

Part Number
Load
Max Work DeflectionBand LengthFatigue Life (cycles)Width
Free I. D.
Thickness
A 3X50-SL04D160.23
12"
16"
20,000
0.25"0.516
0.004
A 3X50-SK04D150.32
12"
15"
13,000
0.25"0.438
0.004
A 3X50-SL05E170.36
12"
17"
20,000
0.3125"0.656
0.005
A 3X50-SH03C100.37
8"
10"
2,500
0.1875"0.219
0.003
A 3X50-SK04E150.4
12"
15"
13,000
0.3125"0.438
0.004
A 3X50-SL05F300.43
25"
30"
20,000
0.375"1.0
0.005
A 3X50-SH04C140.49
12"
14"
2,500
0.1875"0.297
0.004
A 3X50-SK05E160.49
12"
16"
13,000
0.3125"0.563
0.005
A 3X50-SL06F240.52
18"
24"
20,000
0.375"0.781
0.006
A 3X50-SH04D140.66
12"
14"
2,500
0.25"0.297
0.004
A 3X50-SL06G240.7
18"
24"
20,000
0.5"0.781
0.006
A 3X50-SK06F230.71
18"
23"
13,000
0.375"0.672
0.006
A 3X50-SH04E140.83
12"
14"
2,500
0.3125"0.297
0.004
A 3X50-SL08G310.93
24"
31"
20,000
0.5"1.047
0.008
A 3X50-SK06G230.95
18"
23"
13,000
0.5"0.672
0.006
A 3X50-SH05E151.03
12"
15"
2,500
0.3125"0.359
0.005
A 3X50-SK08G301.26
24"
30"
13,000
0.5"0.875
0.008
A 3X50-SL10J331.46
24"
33"
20,000
0.625"1.328
0.010
A 3X50-SH06F211.48
18"
21"
2,500
0.375"0.438
0.006
A 3X50-SK08J301.58
24"
30"
13,000
0.625"0.875
0.008
A 3X50-SH06G211.97
18"
21"
2,500
0.5"0.438
0.006
A 3X50-SK10J321.98
24"
32"
13,000
0.625"1.109
0.010
A 3X50-SL12K422.09
30"
42"
20,000
0.75"1.578
0.012
A 3X50-SK10K322.37
24"
32"
13,000
0.75"1.109
0.010
A 3X50-SH08G282.63
24"
28"
2,500
0.5"0.578
0.008
A 3X50-SL12P422.8
30"
42"
20,000
1"1.578
0.012
A 3X50-SK12K402.84
30"
40"
13,000
0.75"1.344
0.012
A 3X50-SH08J283.29
24"
28"
2,500
0.625"0.578
0.008
A 3X50-SL15P463.5
30"
46"
20,000
1"1.984
0.015
A 3X50-SK12P403.79
30"
40"
13,000
1"1.344
0.012
A 3X50-SH10J294.12
24"
29"
2,500
0.625"0.734
0.010
A 3X50-SL15R464.37
30"
46"
20,000
1.25"1.984
0.015
A 3X50-SK15P424.74
30"
42"
13,000
1.0"1.672
0.015
A 3X50-SH10K294.95
24"
29"
2,500
0.75"0.734
0.010
A 3X50-SK18P475.69
32"
47"
13,000
1.0"2.0
0.018
A 3X50-SL20R545.83
36"
54"
20,000
1.25"2.625
0.020
A 3X50-SH12K365.94
30"
36"
2,500
0.75"0.875
0.012
A 3X50-SL20S546.99
36"
54"
20,000
1.5"2.625
0.020
A 3X50-SH12P367.92
30"
36"
2,500
1.0"0.875
0.012
A 3X50-SL25S598.74
36"
59"
20,000
1.5"3.297
0.025
A 3X50-SK20S529.48
36"
52"
13,000
1.5"2.219
0.020
A 3X50-SH16P3810.6
30"
38"
2,500
1.0"1.156
0.016
A 3X50-SL25U5911.7
36"
59"
20,000
2.0"3.297
0.025
A 3X50-SK25S5711.9
36"
57"
13,000
1.5"2.781
0.020
A 3X50-SL31U6914.4
42"
69"
20,000
2.0"4.078
0.031
A 3X50-SK25U5715.8
36"
57"
13,000
2.0"2.781
0.025
A 3X50-SH20R4716.5
36"
47"
2,500
1.25"1.469
0.020
A 3X50-SK31U6819.6
42"
68"
13,000
2.0"3.438
0.031
A 3X50-SH20S4719.8
36"
47"
2,500
1.5"1.469
0.020
A 3X50-SH25S4824.8
36"
48"
2,500
1.5"1.828
0.025
A 3X50-SH25U4833
36"
48"
2,500
2.0"1.828
0.025
A 3X50-SH31U5840.9
42"
58"
2,500
2.0"2.266
0.031
Available from our distributor, Stock Drive Products. Tel: 516-328-3300

Material Thickness2,500 cycles10,000 cycles20,000 cycles75,000 cycles150,000 cycles
Coiled Dia.LoadCoiled Dia.LoadCoiled Dia.LoadCoiled Dia.LoadCoiled Dia.Load
0.0020.151.30.171.00.220.650.330.320.440.17
0.0030.222.00.251.50.321.00.480.500.660.26
0.0040.302.60.342.00.441.30.650.650.890.35
0.0050.363.30.432.50.551.60.810.801.110.44
0.0060.444.00.513.00.652.00.951.001.330.52
0.0080.595.20.694.00.872.61.281.301.780.70
0.0100.736.60.865.01.083.31.591.602.220.87
0.0120.878.01.036.01.304.01.912.002.671.04
0.0141.029.31.207.01.524.62.222.303.071.20
0.0161.1610.61.378.01.735.32.532.703.601.40
0.0181.3111.91.549.01.965.92.853.004.001.56
0.0201.4613.21.7110.02.186.63.203.304.441.74
0.0221.6114.51.8911.02.377.23.483.604.891.91
0.0251.8116.52.1412.52.728.24.004.105.552.18
0.0282.0418.52.4014.03.049.54.484.606.232.44
0.0312.2620.52.6515.53.3610.24.945.106.902.70

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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