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.

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