Constant Force Springs

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

Constant force springs (also called constant tension springs) provide linear force/tension. The spring force remains nearly constant from extension to retraction. Constant force spring motors provide rotational energy to move or turn components in many devices. The rotational energy, or torque, is nearly constant from extension to retraction. Our constant force springs and assemblies can eliminate costly and complicated motors decreasing your device size and cost.

Constant force springs provide:

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

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.

Industrial Constant Force Spring Applications3-d drawing of a constant force spring.

The constant force spring can be used to counterbalance items such as sash style windows in 1/2″ & 3/4″width series, for both wood & vinyl construction. Also doors, display racks, trays and counterbalancing various hi-tech medical and industrial articulating arms, specifically surgical robots and heavy industrial manufacturing robots. Military and aerospace requirements are satisfied by using constant force springs to counterbalance crew and cargo doors on aircraft and service hatches, for undersea missile launch applications, and U. S. Navy UAV (drone) recovery mechanisms. We have designed and manufactured suspension components that are in use currently in NASA’s Mars Curiosity Rover.

  • Window Manufacturing – Custom constant force window balance springs (including the SideLoad® & the Drop-In constant force balance systems)
  • Electric Motors – Carbon motor brush springs applying a constant force (or pressure) to brushes to minimize wear and increase efficiency of motor life (single and double configuration)
  • Point Of Purchase – Display trays and racks depend on variable force or constant force springs to provide a “self-facing” feature designed into the point of purchase retail product
  • Medical – Counterbalancing needs within the medical equipment design field, consisting of computer monitors in fixed and mobile applications, dental x-ray equipment articulated arms, as well as medical equipment drawer closing mechanisms.
  • Military & Aerospace – Applications include counterbalancing of aircraft cargo doors, as well as interior and exterior aircraft motion control mechanisms.

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.

Material Thickness 2,500 cycles 10,000 cycles 20,000 cycles 75,000 cycles 150,000 cycles
Coiled Dia. Load (lbs.) Coiled Dia. Load (lbs.) Coiled Dia. Load (lbs.) Coiled Dia. Load (lbs.) Coiled Dia. Load (lbs.)
0.002 0.15 1.3 0.17 1 0.22 0.65 0.33 0.32 0.44 0.17
0.003 0.22 2 0.25 1.5 0.32 1 0.48 0.5 0.66 0.26
0.004 0.3 2.6 0.34 2 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 0.8 1.11 0.44
0.006 0.44 4 0.51 3 0.65 2 0.95 1 1.33 0.52
0.008 0.59 5.2 0.69 4 0.87 2.6 1.28 1.3 1.78 0.7
0.010 0.73 6.6 0.86 5 1.08 3.3 1.59 1.6 2.22 0.87
0.012 0.87 8 1.03 6 1.3 4 1.91 2 2.67 1.04
0.014 1.02 9.3 1.2 7 1.52 4.6 2.22 2.3 3.07 1.2
0.016 1.16 10.6 1.37 8 1.73 5.3 2.53 2.7 3.6 1.4
0.018 1.31 11.9 1.54 9 1.96 5.9 2.85 3 4 1.56
0.020 1.46 13.2 1.71 10 2.18 6.6 3.2 3.3 4.44 1.74
0.022 1.61 14.5 1.89 11 2.37 7.2 3.48 3.6 4.89 1.91
0.025 1.81 16.5 2.14 12.5 2.72 8.2 4 4.1 5.55 2.18
0.028 2.04 18.5 2.4 14 3.04 9.5 4.48 4.6 6.23 2.44
0.032 2.26 20.5 2.65 15.5 3.36 10.2 4.94 5.1 6.9 2.7
Constant Force Springs

Category: , , , , ,

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 Constant Force springs for all purposes, and we are here to work with you on any of your customization needs.

TOP
website security