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I Forge Iron

Coil spring failure

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On the weekend, I planned to make some hooks for bowl turning on a bowl lathe from some coil springs. I heated the  springs in a coal fire with air blowing through it from a vacuum cleaner. At first, the straightening of the spring seemed to be going well; I was hating one end, placing over a metal post in the ground, and pulling to form a straight rod. On the third heating however, I went to pull the spring out of the forge, and it came apart into two pieces. Once cooled, the broken end seemed to have a very grainy texture (see photo). I promptly gave up, as I was worried that I might have got hold of the wrong coil spring.

I would appreciate your input on this. Is this grainy texture normal, or is it a sign that the steel is not good enough to make tools with? I am also wondering why the spring came apart in the way it did? I suppose there was a chance that the spring had a preexisting weakness (it was from a used car). Finally, do you think it is worth persisting with the spring, or should I find another or fork out for some proper tool steel?

Thanks in advance,



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Yup, it is not a problem with the spring metal or the spring you chose but it is used error. You overheated it. The higher the carbon in steel the more narrow the heat range you can heat it to and work it. 

I wouldnt try working with that section that was overheated as it will only fail more now. 

Getting the right heat on mystery metal is a learning curve. 

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Mr. Cabbages,

Excessive heat burns the carbon in the iron. It becomes carbon dioxide and the steel is essentially now iron. The high heat causes the grain in that steel / now iron, to grow and become crumbly. In other words that metal is essentially trashed. 

I suggest that you try with fresh metal. Read some of the stickies to learn what temperature range you should use for forging that particular metal. The higher the % carbon in the steel the fussier the heat requirements and forging becomes.

Try smithing with iron or mild steel. (low % carbon iron). Get some experience with that and then smith high % carbon steel.

Keep at it,

Good luck,

it come with time and practice.


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On 6/19/2018 at 4:58 PM, SLAG said:

Excessive heat burns the carbon in the iron. It becomes carbon dioxide and the steel is essentially now iron. The high heat causes the grain in that steel / now iron, to grow and become crumbly. In other words that metal is essentially trashed. 

Thanks. I'll have a go at making some tongs from rebar, then maybe I'll give the hooks another go.

Great screen name by the way.

On 6/19/2018 at 5:04 PM, Steve Sells said:

also used metals are always a crap shoot

Maybe I'll practice with it for a bit and upgrade once I'm a bit more sure of myself.

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Stay away from rebar. The carbon content is a mystery. And it can change from inch to inch, & bar to bar. It's no saving in time and money.

Start smithing simpler things and learn a few techniques. (S-hooks,  chisels etc.).

Tongs are, in my opinion not a beginner's project.

Do some reading to avoid a lot of failure and frustrations


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Look easy?

Forget it.

A skilled craftsman makes things look easy.

Dr. Wilder S. Penfield could have made brain surgery look real easy. (he predated the internet).

Adios Muchacho,


I almost forgot springs are made from high carbon steel

Where are you located? I suggest that you put that into your revised ...

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  • 3 weeks later...


I thought I'd add a few things that haven't been mentioned yet.  First, if you're using a solid fuel forge with a blower it's possible to over-supply the fire with air.  The jet of air in the fire can act like a cutting torch.  Starting out, I had a lot of frustrating experiences where the steel wouldn't get hot so I'd crank up the air supply.  One moment the steel was a dull red, the next it was burnt in two.

The solution was a larger, deeper fire, with an air source that is high in volume and low in speed.  Also, patience.  Most youtubers edit out the heating time.  It can take quite a while for a large piece of steel to come up to temperature.  If the fire is deep enough, the oxygen gets consumed before it gets to the stock.  That allows you to get the steel hot without burning it so easily.  

Mild steel is much easier to forge than high-carbon.  Some high-alloy steels exhibit "red hardness" which means they're hard even when glowing red!   As mentioned above, high-carbon has a lower burning temperature so it's less forgiving of mistakes.  Rebar is a truly terrible steel to forge.  If you have a welder, you might use straight sections as welded-on handles to your project stock.  Even then, take the time to grind off the texturing to avoid giving yourself blisters.

As a final thought, I'd recommend you look into buying "drops" from a local steel supplier.  Suppliers often sell steel by the linear foot.  Once a piece is shorter than 18" or so, they put it in the discount "drops" bin.  Steel from suppliers costs less than half what home centers charge for the same material.  Discount bin material cuts another 10% or thereabouts at the place I go.  New steel sufficient to make a set of ordinary tongs would probably cost about the same as what home centers charge for rebar.

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