Making wire springs
This is the first of three parts on making wire springs. In this part we’ll discuss the making of wire springs in general, and the specifics of making wire extension springs. Extension springs are occasionally used in firearms, but not often. However, they are the easiest spring to make and provide a logical starting point.
Wire springs may be made from several materials, but in the shop they are most often made from “music wire”. This is a spring steel (weird, huh?) wire, available in diameters from whispy hair thicknesses of 0.003″ to what you might consider “rod” at 1/4″ and larger. In gun work, wire springs are rarely made from wire more than 0.050″ in diameter. Such wire can be manipulated with common tools and hand pressure.
Music wire, which has nothing to do with music, as far as I know, should not be confused with “piano wire”. It is available in short, straight lengths as well as larger coils. An assortment of straight lengths, such as those sold by Brownell’s is convenient, but a 12″ piece of wire doesn’t make a very long spring and for many tasks longer pieces are required. The assortment is nice to have, but I generally favor buying 1 lb. coils when possible.
In general, the spring manufacturing process is:
- Determine the form necessary to create the spring, allowing for ‘spring back’.
- Remove any ‘set’ the spring may have from its stock form.
- Bend and/or wind the spring on the desired form.
- Perform any finish steps
- Temper the spring in its desired shape.
Step number five is pretty universal, but steps 1-3 vary depending on the type of spring being made.
Step one is the trickiest of steps, and will likely require some experimentation on your part. The ‘form’ for a spring is the mandrel, or other shape that the wire is bent around to create the desired feature. In the case of coils, the spring will naturally open to create a diameter larger than the form. There is no perfect formula (of which I am aware) to predict this “spring back”. If you want a spring that is 1/2″ in diameter you may have to wind around a 3/8″ or even 1/4″ form. The manuals I have say that the exact amount is determined by each spring factory empirically. That is, through trial and error. The good news is that for most springs there isn’t a tight tolerance for inside or outside diameter. For those that are, a little experimentation is in order.
A set of transfer punches makes a good set of mandrels. These can be clamped in a vise, drill chuck, or lathe for ease of winding. I’ll wind my springs on the lathe (without power), but a lathe is not necessary. To use, chuck up a mandrel (punch) and trap the tip of the wire to be used in the chuck as well. If you’re making a mandrel, a cross-drilled hole is a nice way to start.
Step two involves taking any pre-existing ‘set’ out of the spring stock. This is done at the same time as creating the spring, but I broke it into a separate step to emphasize that it is an important step. Music wire normally comes in two forms: sticks and coils. If your wire came as a stick, step two is likely not very important – most spring designs anticipate that wire which is not manipulated should be straight. For that same reason, wire from coils must be straightened before forming. Straightening is normally performed by running the wire through an orifice, or through a set of pins, immediately prior to being formed. If the wire is not straightened, then the tails may have unexpected curves that impact the effectiveness of the spring design. The straightening jig eliminates the curl from the coil and provides a convenient source of tension while winding.
Step three for an extension spring is simplicity itself. Simply wind the wire around the mandrel, keeping tension applied so the wire remains in contact with the mandrel and keeping the loops touching. In this case I turn the lathe chuck by hand while winding the wire on. For extension springs, it’s easiest to go a bit beyond the length, or number of turns desired, and shorten after the fact.
Be careful as you cut the material, or reach the end of the piece being used – the spring will twist violently as tension is released. In this case I wound a spring around a 0.100″ mandrel and ended up with an internal diameter of about 0.130″.
To finish the spring up, figure out the desired length. Grab a full loop (or a little more) and bend it at right angles to the rest of the spring, creating an attachment loop. Clip off any excess. (There should always be excess – you are likely to end up with too little if you try to bend ‘just enough’ – so bend too much then trim). Measure the desired distance and repeat at the other end. For a truly professional appearance (lacking in my example) bend the second end along the same plane as the first.
That’s 95% of the work! We now have a complete extension spring, and all that remains is tempering.
The fifth and final step is tempering. Tempering relieves some of the stresses set up in the spring when it was being formed. Particularly, it relieves the stresses that are trying to push the spring out of position. In doing so, it normalizes, or makes uniform, the pressures that the spring is designed to create. For music wire, tempering should be done at 350° – 500° F for 30 minutes. A cheap toaster oven is adequate to the task, and some (like the one I purchased, new, for $30) – have a timer to make everthing super-simple.
Allow the spring to cool slowly, preferably in the oven, and you should have a spring every bit as good as what you can buy (and often better – given the glut of low-quality hardware on the market today).