Report · since 1996
Every spring we wind is one of three kinds: it pushes, it pulls or it twists. Here is how far each one goes on our coilers, what I'll hold it to, and what I've learned the hard way.
§1 Compression
Open coiled, made to be pushed shorter. The most common spring in any parts drawer and the one most often replaced by guesswork.
| Dimension | What we wind |
|---|---|
| Wire diameter | 0.2-8.0 mm |
| Outside diameter | 2-75 mm |
| Free length | Up to 300 mm |
| Ends | Open, closed, or closed and ground |
| Spring index | Happiest between 5 and 12, mean diameter over wire |
| Run size | 10-2,500 pieces |
§2 Extension
Wound with every coil touching the next, made to be pulled longer, with a hook at each end. The body rarely fails. The hook is where they let go.
| Dimension | What we wind |
|---|---|
| Wire diameter | 0.2-8.0 mm |
| Outside diameter | 2-75 mm |
| Inside hooks | Up to 300 mm |
| Hooks | Machine, crossover, side, extended |
| Initial tension | Wound in to your figure, read on the first-off at two extensions |
| Run size | 10-2,500 pieces |
§3 Torsion
A coil that stores a twist and two legs that hand it on. There is more to get right on these than on anything else in the shop.
The coil body just stores the twist. The legs are what touch your machine, and every bit of torque arrives through them. Make a leg two millimetres too long and the spring pushes on a different spot with a different force. Bend it too tight and it cracks there first.
The coiler winds the body. The legs are formed by hand, on Paulo's bench, one at a time against a fixture made for your job.
A torsion spring has to wind tighter when it's loaded, never unwind, so the hand matters. Stand the spring on end and look at the coils facing you. If they climb up to the right, like the thread on an ordinary bolt, it's right hand. Up to the left is left hand.
A broken spring still tells you. Even half a coil keeps its slope. One warning: don't send me a photo from a front-facing camera. Some of them flip the picture, and a mirrored right hand spring looks exactly like a left.
I get asked for about ninety degrees most weeks. The trouble is that a torsion spring has at least three angles: the free angle, where the legs sit with nothing on them; the installed angle, once it's fitted; and the working angle, at full travel. They can be forty degrees apart, and which one you mean decides the whole spring.
Tell me the free angle if you know it, which leg you're measuring from, and which way it turns when it's loaded. If all you know is how it sits in the machine, send the part it fits on, or a photo of it in place beside a ruler, and I'll work it back. The first-off sheet records the free angle on all three pieces before anything else is wound.
Two bodies wound in opposite hands, joined by a loop in the middle. They balance a load across a wide hinge without twisting it, which is why you find them on seats, lids and hatches.
They are the slowest thing we make. The coiler winds the pair; the centre loop and both legs are formed by hand, and the two bodies have to come out matched or the lid closes crooked. Expect them at the top of the torsion price range, and expect them right.
| Leg form | Used for | Tolerance held |
|---|---|---|
| Straight tangential | Hinges, returns, most lids | Length ±0.5 mm to 50 mm, ±1.0 mm beyond |
| Straight radial | Legs crossing the centre to a post | Bend within one wire diameter of drawing |
| Short hook | Over a pin or through a hole | Hook position ±1.0 mm |
| Offset or double bend | Clearing a hinge knuckle | Each bend ±3° |
| Free leg angle | All forms | ±5° as standard, ±2° when the drawing asks |
| Bend radius | All forms | Never tighter than the wire diameter |
It came in as two halves of a rusty spring in a sandwich bag. Drawing one copied the broken spring, bent leg and all. Drawing two straightened the leg, but the lid wanted to stay open at about 110 degrees, not flop shut.
Drawing three made it a double torsion so the wide lid stopped racking. Drawing four moved it to 302 stainless, a size heavier, because feed dust and the hose had eaten the first one. That version has been on the bin for years. The four drawings are still pinned above the torsion bench, in order.
§4 Materials
Music wire and oil-tempered are on the rack most days. The rest we order to the job. The quote still comes back within 2 working days and tells you how many extra days the wire adds.
| Wire | Good for | Cost against music wire |
|---|---|---|
| Music wire | Small and medium springs that cycle a lot. Our first choice under 6 mm. | 1.0 |
| Oil-tempered | Heavier wire where music wire gets dear. General machinery. | 0.9 |
| Hard-drawn | Light duty, static loads, cheap first prototypes. | 0.7 |
| Chrome silicon | Shock loads and warm spots up to around 220°C. | 1.6 |
| 302 stainless | Wet, washdown, feed handling and outdoor work. | 2.2 |
| 17-7 stainless | Stainless that has to work hot or hard. | 3.5 |
| Phosphor bronze | Electrical contacts, non-magnetic parts, salt air. | 3.0 |
Relative cost is rough, for the same size and run, with music wire as 1.0. The written quote is the real figure.
§5 Out of scope
Ros
§6 Next
Got a drawing or a broken one? Send it and the quote comes back within 2 working days.