Making Wire Springs

Making Wire Springs. Part 1: Compression Springs Posted on April 7, 2011 by GsT 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, shown in coils and sticks 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: 1. Determine the form necessary to create the spring, allowing for ‘spring back’. 2. Remove any ‘set’ the spring may have from its stock form. 3. Bend and/or wind the spring on the desired form. 4. Perform any finish steps 5. 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.

A transfer punch set in the lathe chuck to be used as a mandrel for winding a coil spring 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.

This simple tensioner straightens the wire immediately before it is rolled onto the form 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.

A small bend in the wire can be trapped in the chuck and used to anchor the starting end

The partially wound spring

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″.

The completely wound spring - there are several extra coils to allow for trimming and the formation of 'grasping loops' 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.

Not the nicest spring I've ever made, but functional 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.

Temper the spring at 450° for 30 minutes 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).

Making Wire Springs. Part II: Compression Springs Posted on April 19, 2011 by GsT Compression springs

Once you’ve wound a few extension springs, you’re ready to progress to compression springs. Compression springs are widely used in firearms, and being able to make your own opens a lot of doors in your own designs as well as repair and modification of existing firearms.

The basics are the same: 1. Determine the form necessary to create the spring, allowing for ‘spring back’. 2. Remove any ‘set’ the spring may have from its stock form. 3. Bend and/or wind the spring on the desired form. 4. Perform any finish steps 5. Temper the spring in itsdesired shape. The difference occurs in step three. Instead of winding a spring where the coils touch, we want to be able to wind a spring where the coils are open and evenly spaced. The easiest way to accomplish this is to use the threading gears on a lathe. Other techniques include custom jigs or simply inserting a shim in between the coils as they are formed. Always start as if you were winding an extension spring – that is, with the coils touching. This is what you want at the ends of a compression spring. Don’t worry about winding a particular number of turns, you will trim to suit when the spring is done.

The first coils of a compression spring are wound just like an extension spring Set the threading gear box to the pitch you want for your spring. Make sure you calculate the pitch based on where the center of the wire is – if you set it according to the space you want between coils you will be off by the diameter of the wire. In other words, if you want 1/16″ between coils, you need a courser pitch than 16 TPI. Assume your wire is 0.032″ in diameter (that’s ~1/32″) and you want 1/16″ between coils – you need each turn to be 1/16″ + 1/32″, which is 3/32″ or approximately 11 TPI. Engage the half-nut and wind the spring. As you get better you might try this under power, but on most lathes it’s possible to rotate the chuck by hand, which makes the process much easier to control, albeit slower.

Winding coils at the selected spacing (pitch) Continue winding until the desired number of turns, or length (don’t forget to allow for the closing coils) is achieved. Finish the winding by winding several closing coils in contact with each other. Again, the exact number doesn’t matter, they’ll be trimmed during finishing.

Winding closing coils on a compression spring The spring is now ready to remove from the mandrel, and should look something like this:

The wound spring before trimming Complete the forming steps by trimming the closing coils at either end.

The completed compression spring If you are winding a spring from relatively thick material (as a hammer mainspring) you may want to grind the end flat, particularly if the spring will go into a ‘seat’ in the final application. Heat treat the spring as described in Part I and you’re ready to go.

Making Wire Springs, Part III. Torsion Springs Posted on April 23, 2011 by GsT Torsion Springs The final wire spring to cover is a torsion spring. In its simplest incarnation a torsion spring is just a stick of music wire with a few twists, usually 2-5, wound on a mandrel, with the ends left straight. That

version is so uninteresting that we’ll proceed directly to a more interesting incarnation: AR and AK hammer springs. (The AR series rifles also use a torsion spring for trigger return). This sort of spring is really two torsion springs with a linkage in between that engages the hammer. For those that are unfamiliar with such a spring, here is the spring from an AK-47:

The hammer / trigger spring from an (Yugoslavian) AK-47 The AK-47 is one of a few designs that have the additional feature of being made from material which is actually a pair of twisted wires. For our purposes here, we’ll wind a torsion spring from a single piece of music wire to replace a factory AK spring.

There are three key measurements that we need: 1. The distance from the center of the ‘axle’ or pivot pin, to the area on the hammer where the spring arm should apply its force. 2. The width (plus a small allowance) of the hammer, and 3. The diameter of the bosses on the hammer that the spring windings will rest on. The first dimension is a direct measurement. The second is the width of the hammer plus 0.01″-0.02″. The final dimension is easily ignored by using a mandrel the diameter of the bosses on the hammer. By doing so, the spring will ‘unwind’ enough after forming to ensure a loose enough fit that there is room for it to tighten as the spring is tensioned.

Draft of dimensions taken from an AK-47 hammer Making a hammer spring requires special fixturing. In essence the fixture is an axle (mandrel) of the correct diameter, around which rotates a form, of the desired width, which holds a bite (the place where the spring material doubles back) at the appropriate radius. Add to this something to straighten / tension the wire before it is wound, and you have everything you need. There are many ways to make a fixture that satisfies these requirements. I’ll make mine as three units: collars to account for the diameter of the bosses, a form which factors in the hammer width and bearing surface, and a tool to maintain tension and straighten the wire as it’s being wound. As an arbitrary choice, I’ll use a 1/4″ axle for the assembly to work on. It’s worth noting that the easiest way to do this might involve using the hammer itself as a form and collars with only the addition of a tensioning tool, but a custom tool will give a little more control. Start by making the form. The form for this AK replacement spring will be 0.300″ wide (that’s the width of the AK hammer (0.270″) pluse a 0.030″ allowance. It will trap the “bite” of the wire at 0.575″ from the center of rotation. The center of rotation will be a 1/4″ hole to fit the axle. I square up a piece of material that’s close to the correct dimensions, thin it to 0.300″. At that point I’ll layout two lines – the axis on which the axle hole (1/4″) will be drilled and the line that must trap the bite 0.575″ away.

The blank for the form, with the pivot hole center-punched and a line where the bite will be captured. I’ll then saw a notch to capture the “bite” – the notch must be wide enough to accommodate the wire I’ll use – extra width won’t hurt. You can double up blades on a hacksaw to do this, if necessary.

The notch added to the form. With the notch cut, I’ll go to the mill or drill press and drill the axle hole – that’s it for the form.

The form is ready for use. Next, I’ll make the collars. I’ll start by drilling some stock 1/4″ for the axle, then turning it to the diameter of the hammer bosses (0.390″). That done, I’ll part off two pieces 1/2″ long. (The windings should only take up 1/4″ or so, so a great deal of width is not required).

Bushings to match the diameter of the hammer where the spring coils sit. Next a tensioning tool is needed. It needs to capture, and tension, two legs of the spring, rather than just a tail as in previous spring types. A single screw adjustment ensures that tension is even over both legs. I made mine from an ‘L’ shaped piece of 3/8″ stock, so I could mount it in a standard tool holder. A small bar of 1/4″ strap serves as the tensioning device. Tension may be adjusted by the single 1/4″-20 screw.

The wire tensioning tool, inserted into a standard quick change toolholder for use in the lathe. A lathe is not at all necessary to wind a hammer spring, but it’s convenient in this case. Anything that can hold the tensioner and axle will do. The spring is started by making a bite in the spring that is the width of the form. The legs are placed through the tensioner and the bite is placed in the notch on the form. The collars are held in place by whatever means are expedient. (My means look especially improvised – but they work!)

The winding setup, ready for music wire. Unlike previous springs, this one must be wound the exact number of turns desired as the straight tails are part of the final product. By rotating the form, the coils are wound.

Starting the spring. The spring looks a bit ugly here because I released winding tension to take the picture. Complete the winding by snipping the ends of the spring stock and removing the raw spring.

Completed winding of the hammer spring - only finish work is left. I took a practice run and produced a mediocre spring, the next was what I wanted. For the AK spring, the tails have a bend after the straight portion – in this way they serve double duty, fulfilling the function of the trigger return spring as well as the hammer spring. Bend the tails, trim, then bend the trimmed ends. The final spring fairly resembles the spring it is patterned after. Here it is, installed on an AK hammer:

The completely formed spring, installed on an AK-47 hammer. Temper the spring in the usual way, by baking at 450* for an hour. If you’ve built AK ‘kits’ then you’ve probably replaced the factory trigger with US made parts to be in compliance with 922r – winding springs for the old parts makes them usable in other projects (bearing in mind that 922r still applies – you may not use more than 10 ‘counting’ parts in a firearm).

Happy winding!