Extension Springs. A Guide To the Manufacturing Process

As part of our continuing series to simplify some of the concepts around spring manufacture we look at the manufacture of the extension springs. It is helpful to consider the process from the perspective of creating the product manually so as to better visualise the process and concepts involved. It goes without saying that at Transworld Engineering we have the tools and machines to automate this process for you. If you would like to learn more, then why not book a visit to our showroom.

The following section will explain how to manufacture extension springs

Wire Length

When creating individual springs for testing There is little need to calculate the precise length of wire required per spring for manufacturing short extension springs with wire up to approximately 0.250" or light wire. However, it would help if you had a sufficient buffer of extra length. To estimate the wire length, you can take the actual measurement of the spring's length. Divide the wire length by wire size to calculate the estimated number of coils in the spring. Multiply that figure by 3.3 (an exaggerated Value of Pi). It will result in a wire a little longer than your requirement, which should not be an issue as you can use the first few springs in the loop making setup.

Coiling the First Trial

You are now ready to manufacture the extension spring.

Cut a piece of wire in the correct length. In the case of light wire, you can undo the wire and put it in front of the winding machine or lathe. To avoid tangling of wire, start by taking the wire end inside the coil as your starting end. You may coil multiple springs simultaneously by cutting off a longer wire length if you want to coil short springs.

You can now fire up the oven while ensuring that other people in the area remain out of danger while completing the rest of the process.

You need to put the wire into this setup and bring the wire guide to the left side near the pickup pin.

Begin the coiling process. Move the chuck carefully while ensuring that the wire rests on the pickup pin, which in turn should be seated on the wire guide. You can now allow a few coils to lay down on the finishing plate.

Once you lay down a couple of first coils on the finishing plate, you can proceed to the next step. At this point, you need to ensure the functioning of the following two processes simultaneously.


1. Move the wire guide slightly to the left side. You should ensure a gap between the two initial coils while laying down the wire over the finishing plate. At the same time, you should not let the wire run over itself when you turn the finishing plate.

The idea of keeping a gap controls the "initial tension." Such initial tension is the vital force in the wire, which applies some pressure on the spring to break the coils apart. For example, there is enough initial tension in Garage door springs. However, there is hardly any initial tension in slinky toys, which are essentially extension springs without any loops.

2. You have to discontinue winding if you notice any of the following two events

a. You have got to the point beyond which you can't approach your lathe machine's "off" switch.

b. You don't have any more wire left.

Now, the wire guide has comes closer to the endpoint of the finishing plate.


Back off the chuck to allow the spring to remain loose on the finishing plate. In case you are using a light wire, you may hold the spring body close to the chuck and pull the dogleg out. It will loosen your grip to allow the coils to unwind slowly. Finally, move the wire guide by sliding it and spring off the finishing plate.

Now you can put the spring into the oven to relieve the stress. Please note that springs manufactured from stainless steel will expand slightly with the heat. On the other hand, springs made from music wire will contract a little.

After you have completed this process, you should allow the springs to air cool. Afterward, you can check the diameter for accuracy. If you have followed it properly and ensured the setup as explained, you should get the exact diameter you had planned.

Now observe the coils of the extension springs. All those coils must lay flat against each other up to the end of the spring body. If you notice any gaps in the spring body, it implies that you had allowed the wire guide to slide to the right side at the time of coiling.

Spring Manufacture  - A Brief Guide



Springs can be created from various designs to take care of a need. Where it will be used plays a role in the right option. All springs will become stressed when they are under a load. The spring in place must be able to take on the amount of stress with that particular setup. Otherwise, the stress will cause the spring to become deformed. It won’t keep the original design and it won’t work as it should.

Springs can be created from a wide variety of materials. The specific type of material will influence the overall strength of the spring. It will also determine the amount of stress it can handle. Keep in mind, when the spring wire is heated, that is also going to modify the form of it.


One of the common types is compression springs. When they are at full compression, the coils are going to touch each other. The diameter of the wire multiplied by the number of coils can’t be greater than the amount of space available. Otherwise, the spring is going to stop the motion in play, it will be a mechanical stop.

Any time a compression spring will be used in an environment of high-temperatures, it needs to be longer. A common use under such conditions is within an engine design. The longer length is going to ensure the compression spring is able to work properly, even with the extreme heat. In this scenario, the spring will assume the load and get shorter. At the same time, the active coils will have an increased diameter. This can be a challenge when the spring is in a confined area.


Pay attention to the designated extension limit on extension springs. If they are used beyond that they won’t hold their shape. They will not be able to go back to the original form with all of the coils closed. When they are used in high-temperature locations, they often have extra tight coils with no play in them. This is to prevent the heat from being able to make the spring weakened.


The diameter of the coils will decrease when a torsion spring assumes a load. It can act as a mechanical stop too. This is possible if there is something inside of the coil to stop the action from the spring.


There are plenty of types of materials used to create springs. The most commonly used are the various steel alloys. This includes:

  • 17-7 stainless steel
  • 302 stainless steel
  • Chrome silicon
  • Chrome vanadium
  • Music wire
  • Oil tempered wire


Sometimes, it is necessary to rely on other materials to create springs though. It all depends on the desired outcome. What does the spring need to do and how much of a load does it need to handle? There are exotic metals used to create springs to meet a unique demand. They include:

  • Beryllium copper
  • Inconel
  • Monel
  • Phosphor bronze
  • Titanium



Music wire is a high carbon type of steel. It is often used when a high amount of strength is needed. It is reasonably priced and the quality is excellent. Strings for pianos and guitars are often made from music wire. Many small springs are created from it too. It can’t be plated, but it will contract when heated.


Commonly referred to as OT, oil tempered wire is made from quality steel. It is inexpensive and often relied upon when the outcome doesn’t have to be uniform or offer much strength. It can be plated and it won’t change when it is heated. OT may be rectangle or square shape to help create the right outcome for a given use.



If you need something higher quality than OT, chrome silicon or chrome vanadium could be the solution. They are stronger and offer a higher quality spring. They can be used in high-temperature settings. Of the common uses for such materials is to create valve springs in vehicles. They can be plated and they don’t change when heated.


This is an excellent material for springs because it doesn’t rust. They are often used in locations where there is steam or water. There are two types of stainless steel used to create springs. The 17-7 isn’t going to change when heated but the 302 will have some expansion.



Several of the materials for springs are a good concept, but keep in mind they can’t be plated. This includes:

  • Beryllium
  • Copper
  • Inconel
  • Monel
  • Phosphor bronze

Such alloys are often used to create springs for high-temperature locations. They may be used where there are challenges due to magnetic fields. They won’t corrode so they are a good choice for humid environments. While they do cost more than other materials, they are going to hold up under harsh conditions. They aren’t going to change due to heat.


Due to the lightweight of titanium, it is frequently used in aircraft. It is very strong and durable but it is expensive. There are also special precautions to take when working with it. For example, the wire can become explosive if there is too much stress placed on it. Titanium can’t be plated and it won’t change due to heat.


When a strong material is needed to create the spring, the amount of load it can hold has to be evaluated. This is the order of strength with the strongest at the top of the list:


  • Titanium
  • Chrome silicon and chrome vanadium
  • Music Wire
  • Oil tempered wire (OT)
  • Stainless steel ( 17-7 and 302)
  • Exotic materials

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