How to make a spring

Hello, I am repairing a antique gun which needs two springs, I've got some already annealed spring steel 2mm thick with correct width. To get the angle approximately 125 deg, will it be best to bend it red hot, then how about tempering after. It's a tough spring that needs the hammers to work, any advice will be appreciated as this is the first spring I've made. Bob

I heat-treated new leaf-springs of fairly similar size, for a 7.25"g loco, by quenching them in oil from cherry-red, then lead-tempering them. The owner of a 2" - inch scale steam-wagon told me he'd used the same method for its springs.

These were springs tempered to a temperature corresponding to blue, which is slightly below the melting-point of lead; but too hot for the domestic oven.

Melt some scrap lead in a suitable container - I used a cleaned-out food tin - then soak the polished springs (tied onto wire for retrieving them) for a few minutes while keeping the lead just on melting-point. You can observe a slight pasty stage in it, as it cools, and that's where it wants to be.

I noticed that the steel would turn blue, or nearly purple, only where exposed to the air. That submerged, stayed bright.

The advantage of liquid tempering is that provided you can control the temperature reasonably closely, as by watching for the crystallising to start, it allows the steel to soak evenly. I have not experimented further but alloying the lead with soft-solder may reduce the melting-point for less tempering.

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You can also temper small items like leaf-springs on a piece of fairly thick steel plate or a shallow sand-bath heated from below, and there were recent references on this forum to using a bath of brass-filings. That was new to me, but I did note the caution that the filings need be clean, not contaminated with oil. (It didn't say how you wash filings...)

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(Tempering in lead copies in a small back-garden scale, the industrial practice of using various molten salts.)

Thanks Graham, I've got some lead and will give your advice a go.

Thanks Bob

Hi Bob, did you mean the steel is Annealed or Hardened? If annealed it can be bent to shape rather easily, if hardened it will have to be heated red to bend it. However in both cases the shaped spring will have to hardened by quenching, probably in oil, before finishing by tempering.

Dave

Annealed or hardened, I would heat it to red to make that bend. Niko.

Bob, I have made several springs like this. Yes you need to heat them red hot to make the bend. You may need to heat it several times to get the 180 deg. bend tight so that there is no hinge type movement at the bend. the power in the spring should come from the spring leaves, not the bend. Do your bending and shaping in a fully annealed state. To temper the spring, heat it until red (non-magnetic) and quench, usually in oil. Then reheat to desired stiffness. I usually shoot for 500-600 deg F. If too soft, reheat, quench and re-temper to a lower temp, or to a higher temp if too hard. There are numerous temp tables on the internet.. Good luck. Rick

Hello,

Thanks for the replies chaps. For Dave the spring steel I've brought states that its annealed. I will have a go at the springs when this nice few days are over, need some sun.

Bob

I would definitely bend that spring at red heat to avoid it cracking .Colin

I have been informed on the forum that Gauge Plate will be a good material to make this spring. I have made the spring and now need to harden and temper this gauge plate, would it be best to heat to cherry red, in water or oil then heat to straw. I am making some copies of the gun so seven springs in all are to be made.

Thanks Bob

You need to talk to one of the leaf spring manufacturers. I know they can temper a spring to many different tolerances using the same spring, so there must be a bit of tech in it. IE initial temp & then plunge time & medium used.

Years ago i worked with a performance shop, getting the spring rates for my Calibra turbo which we were lowering. The same springs were re treated several times before we got them right.

Steve.

Edited By Steviegtr on 09/04/2021 15:26:04

Not convinced Gauge Plate makes good springs but it's worth a try!

Gauge Plate is made of what the Americans call O1. Similar to Silver Steel except it's oil hardening, not water. Pre-heat a domestic oven to 200C, then heat as per Silver Steel to red heat before plunging into about a litre of Cooking Oil. Remove immediately and leave in the oven. This website suggests an hour to temper for wood-working.

Proper spring steel is common as muck except when needed in small quantities! Noggin's End and others sell spring steel for loco and other small leaf springs, but not thick enough for your job. No problem getting it in the USA were knife making is a hobby. I couldn't find anyone in the UK selling suitable thicknesses in other than wholesale quantities. I'd look for a scrap vehicle leaf spring or repurpose a wrecking bar.

Many suppliers of wrecking bars available; I think they all are all made of spring steel, and the example is made from 1045 which is suitable. It will need to be softened by annealling to make the parts, and then rehardened by heating to red-heat, plunging in water, and warming to straw.

Can you report back if gauge plate works OK as a spring?

Dave

Sod, I have some proper common as muck spring steel 1/16" thick x 6 1/2" wide, about 4 pieces 4ft long, I will never use all this so if anyone wants a piece, FOC but pay the postage, send me a PM.

Chris Gunn

Re my surplus spring steel, I should have said I will cut it up into smaller pieces, so plenty to go around.

Chris Gunn

Bob, don't waste your time with Gauge plate, completely the wrong material, get some EN45 Spring steel, you defiantly must forge the spring when red hot, you need to keep a small gap, say 0.010" at the heal of the bend. File to shape and ensure the two legs have an even taper. Harden from red heat in oil and temper to a little over 300*C I usually go for 320*C

Good luck John

Thanks for the replies chap,

Correct about gauge plate, the spring took me some time to cut out of solid, red heat to oil, then a very dark straw., the spring shattered. This was made before recent advice not to make out of gauge plate I brought some annealed spring steel, just over cherry red then in oil and then just starting to go blue then in water. the spring seemed ok , I bent it and the spring returned to size. I put the spring in the gun, and half hour later the spring broke in half under no pressure,the spring broke on the base where no bend was made.Obviously getting the correct temperature which I'm not doing,

Bob

I would soak at cherry red for a longer time than usual - to anneal out any stresses caused by the bending, then your oil quench.

Finally, temper way past straw colours, you need to be past dark blue for a spring.

Neil

Don't despair, you're getting close!

I suspect 'just over cherry red' is too hot. What's meant by 'cherry red' isn't clear, I think it means glacé cherry colour as seen in dim natural light, not full daylight or an artificially lit workshop. May be easier to test temperature with a magnet. Steel loses magnetism when it's hot enough to quench. Try warming to dull red and seeing if a magnet is attracted to it. If not, quench, job done! Otherwise warm the spring to a slightly brighter red and test again.

I think the tempering temperature is too hot as well. Light straw yellow ( 205°C ) rather than Blue ( 340°C ). Wikipedia says 'tempering in the range of 260 and 340 °C causes a decrease in ductility and an increase in brittleness, and is referred to as the "tempered martensite embrittlement" (TME) range. Except in the case of blacksmithing, this range is usually avoided..."

I think the failure was caused by a crack started by cooling too fast from a high temperature, that developed in steel made more brittle, stressed and crystalline by too hot tempering. The spring might have been OK if it hadn't been tempered at all!

I learned something about quenching by watching 'Forged in Fire' on TV, which is like the 'Great British Bake Off' except Americans make historic knives and swords. Old springs are often used to make blades.

Even though the competitors are experienced, the quench often goes wrong. Blades stay soft, warp, and crack. Sometimes the metal is accidentally overheated enough to remove Carbon, converting the blade into useless mild-steel or worse. Rule of thumb, the smith has three attempts at quenching, after which the blade is scrap.

Cracking and brittleness often appear only during the brutal test phase - many a perfect looking knife shatters on impact.

Lesson learned: judging the right temperature for a quench is a little difficult even for chaps who have done it before; the right temperature has to be held steady for a certain time, and then cooled at the right rate. The whole item should be at the same temperature, not white hot in the middle and dull red at the ends. Cooling in oil is preferred because quenching in water is high-risk. Dithering and excessive haste are both bad! Interestingly, blades are often left untempered, but that may be because edge hardness is important in cutting tools. I think springs should be tempered.

There's nothing like doing this stuff to highlight the skill of early metalworkers! I mess up in a modern workshop full of decent tools, good materials, reference books, and access to forum expertise. They did everything from scratch, more like magic than technology.

Dave

Edited By SillyOldDuffer on 07/05/2021 10:43:34

Hi Bob clearly too hard ! Going just blue will be around 300* C you need to be above that at around 310 or 320*C even up to 340*C look a Neil’s colour chart. I temper my springs in a muffle furnace, another point why quench in water after tempering ? The wrong medium use oil. Also do you know for sure what the material is ? rather than spring steel, it make a considerable difference, you need EN45 or EN47 45 is best and traditionally used for gun springs. See you PM’s

John