TOOLING

The Front (Starting) End

For wire between .003' and about .025', you'll be using either a drill or a hand winder to make your springs. For extension or compression springs, no special tooling is needed for the front end of the wire. Just make a 90-degree bend in the wire by hand and stick the bent end in between two of the jaws of your chuck.

For heavier wire, you'll need to make a pickup pin to keep the front end under control. A pickup pin can be made from a square bar, using a grinding wheel:

Notice how the pickup pin has been ground to accommodate both the arbor and the wire.

It's better not to use a three-jaw chuck for heavier wire, but if there's no alternative, you can control the front end of the wire be either drilling a hole in one of the jaws of the chuck and press- fitting a pickup pin into it, or welding a pickup pin onto one of the jaws. Again, it's much safer to use a four-jaw chuck. 'Nuff said

The Back (Finishing) End

To control the back end of the wire, you'll need a wire guide. What kind of wire guide you'll need depends on the type of spring you want to make and the size of the wire you're using.

Extension and torsion springs:

For wire up to about .125", you can make a simple wire guide that looks like this:

For larger wire, you'll need to make a wire guide that fits into the tool post of your lathe:

If the spring you want to make is longer than your lathe, you will need to make some special tooling.

Finishing Tooling

You'll also need to make tools to help you finish the ends of extension and torsion springs. Again, the tooling you'll need will depend on the size of your wire.

Extension springs:

Most often, the ends of extension springs are formed like either loops or hooks. To form these you will need two tools: the first is a set of looping plates, which can be made out of flat steel with a grinder. To make looping plates, first take two pieces of stock (1/4" thick, width about 1½ times the outside diameter of your spring ) and chuck them up in a vise, one at a time. Bend the ends to about 100 degrees. Then, cut off all but a small amount of the end that you bent over:

Using the grinding wheel, carve out a hollow in each end. Taper it down so that the edge is sharp enough to “grab” between two coils of wire.

These plates work best with relatively stiff extension springs. If you find you're having trouble keeping the body of the spring steady between the plates, you can always cut some grooves on the inside face of the plates to help the wire stay put.

Also note that the sloped area that's been ground away at the top of each plate is somewhat larger than the diameter of the spring.

The second tool you'll need to form the ends of extension springs is a hooking rod: again, you can use your grinding wheel to make this tool.

This is a hand-held tool that you'll need a fair degree of control over, so make it about 6-14" long (depending on the size of the spring wire) out of stick that's about a third again as thick as the wire you're coiling.

Notice that the end is relieved to accommodate the wire.

Extended hooks:

You may want to make an extension spring with extended hooks, like this:

The best way to do this is to coil the spring as if it were a torsion spring and then bend the ends over to form the extended hooks (see the page on torsion springs).

If you're making this kind of spring, you'll need to make a different set of plates. The first will be a thin steel plate with one edge ground knife-sharp.

For the other plate, take a piece of flat steel and bend it over just like you did for the looping plates, only bend it over a little more and don't trim quite so much off the end:

You might also want to make a bending pipe to aid in bending wire larger than can easily be bent by hand. Start with a short section of pipe or tubing that's a little bigger on the inside than your wire. Then, simply cut off the end on a diagonal, like this:

See the section on extension springs for how to use the plates and the bending pipe to form your ends.

Torsion springs:

The ends of torsion springs can be formed in a million different ways. The key is to make the bends smooth: the sharper the bend, the more likely it'll break:

If you're using light wire, you can probably use round-nose pliers to form your ends. For medium wire, make a layover plate (above) and use a length of pipe to grab the end of the wire. This will give you enough leverage to get it to bend.

For wire too big to bend by hand, just heat the bend area of the wire with your acetylene torch. Don't get it too hot — just warm it up enough so that it will bend with the help of a piece of pipe.

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Bending jigs

This is the simplest bending jig I know of: it uses tooling you've already made!

In your vise, chuck up a piece of bar stock, maybe a little smaller than your arbor, and a pickup pin suitable for the wire you're using.

Then, when you lay the leg of your spring between the bar stock and the pickup pin, you can use a wire guide to made the leg bend around the bar stock.

Keeping careful track of how much wire is used up making the bend will allow you to make your bends fairly precisely - with practice, within 1/10".

You can also make a more complex bending jig capable of handling virtually any light wire bend:

You can make stops and guides mounted on top of the jig (to control your spring) out of thin steel, and other stops mounted on the side of the jig out of thicker stock — 1/8" works well — to control how far the handle should move (to control the amount of bend).

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Passivating basket

If you're working with stainless steel wire, you'll need a passivating basket. All a passivating basket has to do is hold the springs while they're taking a bath in some nice acid. You can make one very easily using stainless steel mesh. Just bend the edges of the mesh up to form a basket shape large enough to hold your springs, “stitch” the edges together with stainless steel wire, and make a handle, also out of stainless steel.

Don't use anything but stainless to make your passivating basket — otherwise, the acid will eat it alive.

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Grinding stage

A grinding stage is simply a flat piece of material (either steel or wood will work) attached to your grinder. The purpose of a grinding stage is to provide a flat surface that your spring lays on while you're grinding the ends.

Make your stage so that it faces the flat side of the grinding wheel, and is at least as wide as the grinding wheel's side surface.

EQUIPMENT

Winding Machines:

The basic thing you'll need is a winding machine of some sort. A winding machine is something that will pull your wire around and make it coil up into a spring shape. What kind of winding machine you'll need depends on what size wire you'll be working with, and also, how many springs you want to make.

If you want to make more than about 50 springs of one kind, it'll probably be worth your while to have your springs made commercially. You can find out about how spring factories operate: the Addendum also has a list of spring shops that have a Web presence. You can also find spring shops in your area by consulting the phone book.

Light Wire:

For light wire (.003-.025") extension springs, you can use a hand drill mounted in a vise. A variable-speed drill is best: set it on the lowest speed you can.

For light wire torsion springs (up to about .125"), you can use a hand winder:

For light wire compression springs and for medium wire (.025-.187") springs of all types, you should have a lathe. For wire bigger than about .187", you'll need a lathe strong enough to pull the wire: for compression springs in all sizes of wire, your lathe should have a back gear and a working lead screw.

Your lathe doesn't have to be a precision machine. In fact, the heavier the wire you want to work with, the better it is if your lathe is a piece of junk. All it has to have is a working motor, a tool post (for compression and torsion springs), and a reliable back gear, and, also for compression springs, a variable-pitch lead screw.

Other than that, it can be as sloppy as you want.

Wood lathes, by the way, may work for light extension springs if the tooling can be made to fit.

Grinding Equipment

You'll need a grinding wheel for several purposes. The best kind is a double wheel, where you can have a grinding wheel in one side and a cutoff wheel on the other. Metal trades suppliers can sell you the wheels.

For all springs, you'll have to be able to cut away the waste wire from the ends of your springs. You can do this with wire cutters (for wire up to about .062"), with a cutoff wheel, or with an acetylene torch. (One note: an acetylene torch will not be effective on large-diameter stainless steel wire.)

For compression springs, you may want to have the ends ground square with respect to the body of the spring. You can do this with an abrasive wheel. For heavy compression springs, you may need a bigger grinder: a small grinder will take forever.

Also for compression springs, you may want to deburr the inside and outside of the ends after grinding. You can do this with a conical grinding stone mounted in a drill (for the inside) and a regular abrasive wheel (for the outside).

You'll also need a grinding wheel to make some of your tooling: most of the tooling you'll need can be made rough, and a grinding wheel will work just fine.

Finishing Equipment

After you've wound your springs and formed the ends, you'll need to get rid of the stress that bending the wire has caused. To do this, you need an oven. How hot your oven needs to go depends on what material you use for your spring:

Oil tempered wire, music wire, and 302 stainless	500 degrees
17-7 stainless and chrome silicon	650 degrees
Chrome vanadium	750 degrees
Most exotic materials	>850 degrees

It's probably best not to use your kitchen oven for oil tempered wire, chrome silicon, or chrome vanadium. The wire will come coated with oil, which will burn off in the oven. If your oven won't reach the temperature you need, find a potter who has a kiln you can use.

For stainless steel wire, you'll also need a passivating tank to remove the chemical coating on the wire. This is a tank made out of stainless steel (an old sink is fine) and filled with acid.

If you want your springs to be plated, send them out to a plating shop. Don't try to do your own plating unless you're already in the plating business.

Hand Tools

You'll need some basic hand tools:

• A vise (either floor- or bench-mounted)
• Wire cutters (6" diagonal)
• Needle-nose pliers
• Calipers (if dimensions are critical)
• Tape measure (if dimensions are rough)
• Crescent wrench
• Acetylene torch (if working with wire over about .250")
• Bolt cutters (for wire between .080-.250")
• Round nose pliers (for forming the ends of torsion springs)
• Chalk

Testing Equipment

Depending on what kind of machine your spring is going to work in, probably the best way to test a spring is to make one and see if it does the job. Other than that, here are a few ways to perform rough testing on springs.

To test extension springs, you can always hang the spring from the ceiling and load it up with weights on the other end.

For medium-sized compression springs, you can made the spring act as a limited-travel extension spring (see extension springs for how to do this) and test them the same way. This method will not work for light or heavy compression springs — just medium ones.

I don't know of a simple way to make a really accurate testing rig for torsion springs: best bet is to just plug it in and see if it works.

Tooling Stock:

To make the tooling you need, you should have some pieces of flat stock (mild steel) and some bar stock. You'll get the idea of what kind of stock you'll need for your tooling as you read the section on tooling. You can find this kind of stuff at your local scrap dealer or junkyard: they usually sell it by the pound.

You'll also need arbor stock (an arbor is the bar or pipe you use to wrap the wire around to make the spring). Once you know what size arbor you need, visit your local scrap yard: it doesn't have to be pretty, but remember, it does have to be long enough.

If you're working with heavy wire, you may need a welding rig to make your tooling safe.

WIRE SAFETY

THIS PAGE IS IMPORTANT!

Spring wire can be dangerous if not properly handled.

Read this section carefully
before you start working with wire.

 

General Safety:

Springs under load want to return to their original shape. The same goes for spring wire. Spring wire will try to straighten itself out if given the chance: don't let your body get in its way.

Small wire:

Small wire (diameter less than about .025") will not hurt you if it hits you. On the other hand, small wire is nothing more than an edge, waiting for something to cut. Don't use your hand to try to stop wire that's moving, especially if it's moving under power (like being pulled by a lathe). Instead, wait till it stops moving. Gloves are an excellent idea, too.

Medium wire:

Medium wire (diameter from about .025" - .312") is too wide to act as an edge, and usually not massive enough to break bones, but it can raise quite a knot if you get in its way. Again, always keep track of where the ends of the wire are, and if they start to move, get out of the way.

Heavy wire:

Heavy wire (diameter greater than about .312") needs respect. If it gets loose, it can EASILY break bones, or worse.

Stainless steel:

Stainless steel is a lot softer than other types of wire. When cut, the end of the wire is like a knife edge. Always keep track of where the end of the wire is, and keep your hands away from it while it's moving.

 

Handling Wire:

The two most dangerous times are when you're breaking open a coil of wire and when you're actually winding a spring.

Breaking open coils

Once you have your wire, you'll need to take it out of its coil. The coil may be wrapped in paper take that off first.

Under the paper, the wire will be tied. Light wire will be tied with string. Medium wire will be tied with tie wire. Large wire will be tied with metal bands. Whatever size wire you have, remember that the coil should have only two ends. One will be on the inside of the coil, and the other will be on the outside. You'll normally use wire from the inside, to avoid tangling. Always make a hook on the “inside” end so it's easy to find again:

Handling Small Wire in Coils:

To break open a coil of small (up to about .125") wire, cut all the ties except two. Don't cut the closest tie holding the outside end of the wire, and the tie most directly opposite to that one.

To remove wire from the coil, start with the end on the inside of the coil: this will keep the coil from tangling. Grab the end of the wire and cut off the hook. Pull it slightly, until you can see the gap between it and the rest of the coil. Grab the wire at the gap and pull the end free from the tie holding it. Repeat this process, working around the coil, until you have the length you need.

Medium-sized wire:

(.125 - .312") can be handled the same way, except that you should keep three ties instead of two. When uncoiling wire larger than .250", you should lay the coil flat on the ground and always stand in the center of the coil, for safety.

Large wire:

(.312 - .625") needs special handling. First of all, you'll probably be using a hoist or forklift to move the coil, because of the weight. Lay the coil on top of something (a 2x4 or a pipe works great) to keep one end off the ground so that you can pick it up when you're done. Stand inside the coil from now on!

Then, take a length of tie wire and double it over. Loop it twice around the coil, right next to the second tie holding the inside end of the wire. Pull it tight and twist it so that you have a 'pigtail' and the tie wire is too tight to move by hand. Then, cut the first two original ties. Grab the end of the wire and flip it over the coil, so that it sticks out.

Go to the next tie and repeat this process, working your way around the coil until you have the length you need. You can use heavy bolt cutters or an acetylene torch to cut the wire.

If heavy wire gets away from you and starts to come undone all by itself, the very best thing to do is

• Run like hell, and
• Pray it doesn't hit you.

Coiling:

If you're using a lathe to make your springs, you'll be standing there, letting the lathe pull the wire. The lathe will do what you want, but it will not know to stop if things get out of control. So, before you start the lathe, figure out what you're going to do if things go haywire. Know how to stop the lathe, and know which way you can safely run.

Never reach over the wire to get to your lathe controls, especially when working with heavy wire. Reach under it and avoid injury if your wire guide breaks.

Keep the lathe speed DEAD SLOW: with heavy wire, 10 rpm is about right.

Don't grab onto wire that's being fed into the lathe. Stop the lathe and back it off until there's no tension in the wire before you put your hands near.

NEVER try to guide wire by hand. Use tooling.

 

When you're done:

After you've removed wire from a coil, the coil will be looser than it was before. Before you put it away, retie it so that it doesn't tangle up or uncoil by itself. For light wire, use string. For medium size wire, use tie wire. For heavy wire, use tie wire doubled over, looped around the coil twice, and tied in a “pigtail”:

Lastly, make a hook in the “inside” end of the wire, so you can find it again easily when you need to.

 

Storing Wire:

Safety first: always store your wire someplace where kids can't get at it.

Common sense second: keep your wire dry. Steel wire will rust if it gets wet.

More common sense: keep your wire tight. When you're finished working with a coil of wire, make a hook in the inside end (so you can find it again easily) and tie the coil securely. Be especially careful with heavy wire, which should be tied with at least six doubled strands of tie wire, each looped around the coil twice and cinched tight.

Still more common sense: if you live in an area that has earthquakes, tornadoes, hurricanes, etc., be sure that you chock your coils of wire so that they don't get loose and start to move around when mother nature starts acting up.

SPRING MATERIALS

This section will tell you about the different kinds of material that springs are made out of. It will also tell you where to get your wire -- make sure you read the Safety section so you know how to handle it safely once you've got it.

Types of Wire:

Springs are usually made from alloys of steel. The most common spring steels are music wire, oil tempered wire, chrome silicon, chrome vanadium, and 302 and 17-7 stainless. Other materials can also be formed into springs, depending on the characteristics needed. Some of the more common of these exotic metals include beryllium copper, phosphor bronze, Inconel, Monel, and titanium. The following table summarizes the more important properties of each material:

Material	Common Sizes	Properties and Uses
Music Wire	.003-.250	A high-carbon steel wire used primarily for applications demanding high strength, medium price, and uniformly high quality. Guitar and piano strings are made from this material, as are most small springs. Music wire will contract under heat, and can be plated.
Oil Tempered Wire (OT)	.010-.625	This is the workhorse steel spring wire, being used for many applications in which superior strength or uniformity is not crucial. Will not generally change dimensions under heat. Can be plated. Also available in square and rectangular sections.
Chrome Silicon, Chrome Vanadium	.010-.500	These are higher quality, higher strength versions of Oil Tempered wire, used in high-temperature applications such as automotive valve springs. Will not generally change dimensions under heat. Can be plated.
Stainless Steel	.005-.500	Stainless steels will not rust, making them ideal for the food industry and other environments containing water or steam. 302 series stainless will expand slightly under heat: 17-7 will usually not change. Cannot be plated.
Inconel, Monel, Beryllium Copper, Phosphor Bronze	.010-.125	These specialty alloys are sometimes made into springs which are designed to work in extremely high-temperature environments, where magnetic fields present a problem, or where corrosion resistance is needed in a high-temperature working environment. They are much more costly than the more common stocks and cannot be plated. Generally will not change dimensions under heat.
Titanium	.032-.500	Used primarily in air- and spacecraft because of its extremely light weight and high strength, titanium is also extremely expensive and dangerous to work with as well: titanium wire will shatter explosively under stress if its surface is scored. Generally will not change dimensions under heat. Cannot be plated.

Titanium is the strongest material, but it is very expensive. Next come chrome vanadium and chrome silicon, then music wire, and then oil tempered wire. The stainless and exotic materials are all weaker than the rest.

 

Buying wire:

Spring wire is made in common sizes (see table above) and in special sizes to order. The common sizes that are manufactured are available within the ranges specified at intervals ranging from a couple of thousandths of an inch (for the smaller sizes) to sixteenths of inches (for the larger sizes). Metric-measure sizes are available outside the US.

These spring wire materials may be bought from steel suppliers in two forms: coils and straightened- and-cut bars. Unless you are dealing with extremely close tolerances, exotic materials, or need a stock size that is not commonly manufactured, you'll probably find it most economical to buy your stock in coils.

Bought in coils, spring steel is generally sold by the pound: the coils range in size from about 6 inches (for wire under .005') to 7 feet (for wire in the .437-.500' range) in diameter. The smaller coils are generally shipped UPS, while the larger sizes require truck transport as well as special unloading and storage facilities.

Finding a source of supply is as easy as looking in the phone book: if you're in a rural area, try the local library which will have Yellow Pages for the major metropolitan areas -- try Detroit or Los Angeles for starters. You can also contact the Spring Manufacturers' Institute and ask them for a copy of Springs magazine, which is filled with suppliers' advertisements (as well as technically interesting articles). The Addendum also lists some wire manufacturers and suppliers

One caution: you should not order straightened-and-cut wire until you're SURE you know what you want. Once you get your material, you'll find it impossible to return if the bars are an inch too short.

And one note: when spring wire is made, it develops what's known as a 'cast' from being tied into round coils. If you strip wire from a coil, it will likely not be perfectly straight: the 'natural' curvature of the wire is 'cast'. The cast of the wire will introduce an extremely small variance in the physical dimensions of the springs made from the wire -- it's only a problem when you're working with very close dimensional tolerances. Cast is why wire is also available in straightened-and-cut bars.

SPRING DESIGN

If you're trying to make a spring to replace a broken one, you don't need to know a whole lot about design. On the other hand, if you're making a prototype of a machine, for instance, and you don't know exactly what you want, then this page is for you. Here you'll learn some basic data about spring design, which is what you'll need to know to make exactly the spring you want.

General Principles

There are three basic principles in spring design:

• The heavier the wire, the stronger the spring.
• The smaller the coil, the stronger the spring.
• The more active coils, the less load you will have to apply in order to get it to move a certain distance.

Based on these general principles, you now know what to do to change the properties of a spring you already have. For instance, if you want to make automotive valve springs a little stronger than stock, you can a) go to a slightly heavier wire and keep the dimensions and coil count the same, b) decrease the diameter of the spring, keeping the wire size and coil count the same, or c) decrease the number of active coils, keeping the wire size and spring diameter the same. Naturally, you can also go to a stronger material to achieve the same result.

Now, what if you're making a spring from scratch, with nothing to go on in the way of a sample? You can engineer your own design (see the next section of this page for the math), coil a spring, and then test it. If it's what you want, fine. If it's, let's say, a skosh too strong, then you can a) go to a lighter wire, b) open up the coil diameter, or c) increase the number of active coils to get a slightly weaker spring.

Or, if you want to make things really simple, go to the Addendum, where you'll find a few websites that offer online design!

Mathematics:

Naturally, spring design software is available — you can find out where to get it in the Addendum. For the purists (or those who don't want to pay for a program), here's a very short summary of the mathematics of spring design. These equations, by the way, are taken from The New American Machinist's Handbook, published by McGraw-Hill Book Company, Inc.in 1955. I don't pretend to understand them.

There's a lot more in the way of engineering that goes into spring design: these are only the basic equations. If you're interested, you can contact someone who makes spring design software or (gasp!) find it in the library under Dewey classification number 621.824.

Design Limitations:

Depending on what kind of spring you want to design, and depending on where it will be used, your design will be limited:

For all springs: 

• A spring under load is stressed. If you put too much stress on a spring, its shape will deform and it will not return to its original dimensions.
• The material from which the spring is made will have an effect on the strength of the spring: it will also have an effect on how much stress the spring will withstand. The section on spring materials will tell you more about this.
• When you heat spring wire (which you always do), it may change its dimensions. Again, the section on materials will tell you more about this.

For compression springs:

• If the spring will set solid (compress all the way, so that all the coils touch each other) at the limit of its travel, the diameter of the wire times the number of coils cannot be greater than the space allowed, unless you want the spring itself to act as a mechanical stop to the motion.
• Springs that operate in a high-temperature environment (like for instance inside an engine) will need to be made slightly longer to compensate for the fact that the heat may have an effect on the length of the spring. The section on finishing will tell you more about this.
• As a compression spring assumes a load and shortens, the diameter of the active coils will increase. This is only a problem when the spring has to work in a confined space.

For extension springs:

• There should be some mechanical limit on how far the spring will extend, or the spring will lose its shape and not return to its initial condition with all coils closed.
• Extension springs operating in a high-temperature environment may have to be coiled extra-tight, as the heat will tend to weaken the spring. The section on extension springs will tell you more about this.

For torsion springs:

• When a torsion springs assumes a load, the diameter of the coil body will decrease. If the spring has something inside the coil, it will act as a mechanical stop to the action of the spring.

 

Buying Design:

If you want to have a mechanical engineer design your spring, your best bet is to call a spring shop. You can find spring shops in the phone book. If your phone book doesn't list any, go to the library: they should have phone books for major cities where spring factories are -- try Detroit or Los Angeles if there are none in your area.

A spring shop will generally do the design work for you for a small charge. They will also try to get you to let them make the spring for you, which you may or may not want.

The section on spring shops will tell you more about how their business operates. The addendum will give you links to spring shops, suppliers, people who make spring design software, and a whole slew of other stuff.