Creating Long Acoustic-Kinetic "Reverb" Springs

At MakerFaire 2015 and the Oakland Aeolian Day, many people inquired about how I built my Acousto-kinetic sculpture called "Chatty Spring Ballz". The motion characteristics needed for this sculpture required long "wiggly" style extension springs. It's nearly impossible to find long industrial springs that have a lower overall spring tension that would support the kind of mechanical "jiggle" and "wobble" I wanted to display, so I was forced to make my own.

While there is already a fine Instructable on how to create small springs using a hand-held chorded drill and short wire segments, this method would not work well for very longs springs, very wide springs, or if you lack sufficient strength to both hold up a drill press and maintain consistent wire tension around the mandrel, all while simultaneously preventing music wire from tangling on itself or catching on the box. ...So I chose to make my springs on a lathe. And this Instructable will show you how you can too.

Step 1: Tools You'll Need

Spring wire (I ordered Precision wire from Grainger in diameters ranging from .020" to .037", e.g. http://goo.gl/EbhLkf)
Wire cutter with Rockwell hardness greater than C60 (and be sure that the cutter is rated for the wire thickness that you will be using! More on that to follow). *
Cylindrical mandrel (1ft long minimum)
Diagonal cutters
Lathe (small variable speed lathe at a local DIY hackerspace is recommended)
Scrub pad (optional, used to remove the filmy "gunk" on the wire before winding. Makes the springs look nicer.)
Needle nose pliers (optional but recommended) *
A second person (optional but recommended) *
Leather gloves (to help maintain tension on the wire while winding).

*You can sometimes get lucky and find vintage hard steel wire cutters on Ebay, but if all else fails, you can find an affordable pair of wire cutters at "IRWIN Tools VISE-GRIP Wire Stripper and Cutter, 5-Inch (2078305)": http://goo.gl/T3SrOv

*Needle nose pliers are useful to kink the wire after cutting from the box (to prevent loosing the wire in the box forever!).

*A second person is highly recommended to help maintain tension and check for wire tangles as it's feeding into the lathe.

Step 2: Important Factors to Consider

"Spring Back"

There is always a certain amount of "spring back" after this kind of wire wound is formed around the mandrel. This essentially means that you will always get a slightly wider and shorter spring than what you originally wound around the mandrel. The amount of spring back in a wind varies according to a number of competing factors but here are a couple of important ones to consider:

The tensile strength of the wire (which gets higher as the wire diameter gets smaller, due to work hardening, see: http://www.interwiregroup.com/interwire-products/... for more details)
The amount of tension on the wire while it's being wound.

Wire Tangles

The increase in tensile strength of very thin wire also means that it is more prone to tangling around itself then thicker wire (this is especially true once it has been cut from the box). In my experience, wire that is .036" thick is manageable in terms of "tangle factor" but .020" thick wire is really challenging once it is cut from the box. For this reason, I recommended that you not cut the wire from the box until you are ready to wind. (...and this is also where my recommendation for having a second person to help you maintain the long wire feed comes in.) If you have a second person present, you can easily manage these issues as the first person winds the wire on the lathe. Without that second person, I would only recommend trying to wind wire of a wider diameter (approx: .036" or greater).

Wire Tension (while winding)

This is another reason why it is recommended to have a second person to help with wire winding. Creating a nice tight extension spring requires some uniform tension and back-bias to be place wire angle relative to the mandrel (more on that to follow). It can be helpful to have a second person to not only help you feed wire, but also maintain a consistent tension on the wire as the winding can become a little tiring on the hand.

Step 3: Figuring Out How Much Wire You'll Need

Even before you start pulling wire out of the box it's good to have a sense of how much wire you will need for the desired size of spring that you want to create. Here's a general formula to measure out your wire length (units in inches).

The minimum length of wire needed for a given spring length will be determined by the following relationship: Lw=D*pi*N = (Ls/T)*pi*D

Ls = Length of spring

Lw = Length of wire needed

T = thickness of wire

N = number of turns needed = Ls/T

D = spring diameter (or diameter of mandrel)

You should add at least an extra 3ft of length to this equation for working slack so then you have:

Lw=(Ls/T)*pi*D + 36

So, for example, using spring wire of .020" diameter, a spring of 6" long wrapped around a .25" mandrel would require at least: (6/.020)*3.14159*.25 + 36 = 271.62 inches (22.63 feet) of wire.

For the "wiggly" style extension springs like the ones I made for my sound sculpture, I found roughly that a ratio of wire size to spring diameter should be about 1/10. So .020" width wire might be best to wind around a mandrel size of .250 (1/4 inch).

Step 4: Getting Wire Out of the Box (...the Right Way)

Surprisingly, removing the wire and preventing tangling can be the most technically challenging aspect of this project.

As the picture shows, on the side of the box there are instructions on how to remove wire from the box. Follow these instructions and DO NOT remove the bundle of wire from the box (especially after the copper wire bands around the wire have been cut)!

1) The box comes with a pre-marked circle opening at the front of the box. Remove it.

2) Then, using diagonal cutters, cut the 3 copper bands that are around the steel wire from the front opening that you have just made.

3) Gently pull the wire out from around the cut copper bands by pulling the wire up from the from of the center of the box.

Step 5: Cleaning the Wire (optional)

The music wire comes with a wax-like film coating (for reasons I have never quite understood). This results in a wire finish that looks very matte and dull.

If visual appeal is important in your long spring project, this film is easily removed with a scrubby pad as shown in the photo. It's also an option to use steel wool or any other kind of abrasive to remove this. The thin layer of film comes off with scrubbing and the difference in shine become very clear after a few passes. It's recommended to clean the wire after you've pulled out the full length of wire you will need. If you can anchor/clamp one side of your wire with a clamp or vise of some kind that is ideal, so that you can maintain tension on the wire so as not to kink it while you are scrubbing the film off.

Step 6: Quick Lathe Safety Instructions (that Are in No Way a Substitute for Actual Lathe Training)

A quick list of some things you should never to do even while working on a small variable speed lathe (like the one pictured here):

Never leave the chuck key in the lathe!
When you are working on a foreign lathe, always test the lathe without anything in it at first to see how it works.
Never wear the leather gloves. Just wrap your hands around the gloves instead. If you wear the leather gloves, there is a risk the lathe will catch on your glove and pull the rest of your body into it!

Step 7: Setting Up the Wire on the Lathe

Cut the length of wire you will be using and make sure that you leave a couple of feet of extra wire from the box to prevent the wire from hiding back in the box (the wire will to become VERY hard to retrieve from the box if this happens). For wire storage, kink the wire connected to the box with a 270deg bend using the needle nose pliers to prevent it from hiding back in the box.

You can either tape one end of the wire to be wound onto the mandrel as shown or clamp the wire into the chuck. I chose to use tape in this situation.

If you're working alone, to keep the wire from tangling on itself, you should anchor the free side of the wire with some kind of heavy weight as shown in the picture. As the wire winds, be sure there is a clear unobstructed path for the wire and metal weight to move as the lathe winds up the wire. If you are working with a partner, you can just have them help guide the loose wire coils as they are being consumed by the lathe windings and check for any tangling, etc.

Step 8: Winding!

Start the lathe at a very slow speed to get a couple of turns established and then slowly increase the speed as the tension gets established.

To make an extension spring, you will want to provide a significant amount of wire tension as it's winding. To ensure that your spring turns remain snug after it is wound, provide some amount of "back bias" on the wire as shown in the picture as shown by holding the wire at a slightly less than 90deg angle relative to the mandrel rod while maintaining a constant wire tension as the mandrel is turning.

When you have roughly only a foot of wire left, stop the lathe, place your hand with a glove over the wound wire, and cut the wire from it's weight, or cut weightless the wire at a short distance from the wind. Slowly loosen the tension of your hand from the wire to let the spring unwind under your glove. Once it's released, you can remove the glove, tape and mandrel.