Leaf Springs

A

AfterTFD

Joined
Oct 28, 2007
Messages
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The cheapest idea I've heard for making knives is to straighten a leaf spring and only work with it cold so no heat treatment is needed. Is this idea actually feasible?

Would straightening a leaf spring with a press or hammer cause internal stresses that would reduce the strength of the knife?
 
I would think you'd develop massive stresses hammering steel into knife shapes cold, unless you're talking about filing or shaping on a grinder. Straightening it hot (meaning at the proper temperatures) will reduce the possibilities of stress fractures but I used to have a lot of issues with used steel.
 
I wouldn't go this way. A bar of steel is awfully cheap to begin with and the supplies to do a basic heat treatment on 1080/1084 aren't expensive either.

If you really didn't want to heat treat, then there are a couple folks on here that might be willing to help out.
 
That's the best way of spoiling and making brittle a real good piece of steel that could yeld very good knives with very good edge and spring in them.
 
cold straightening a spring then making a knife out of it is:
taking a piece of reasonble steel, applying force beyond it's yield point (hoping you do not find it's failure point) grinding it(supplying it with thousands of potential stess risers in the process) reducing its crosssection, and then using it in an application that demands the highest performance of steel.
in short, that plan would be ruining already abused steel, then trying to use it for something that takes a lot of time to make and demands the most out of the best steel.
it's your time and tendonitis,
do yourself a favor, get new steel, forge it hot if you are going to change it's shape, etc.
heat treating is the soul of the steel, heat treating for spring properties is not what you want for edge retention
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You can heat treat for spring properties AND edge retention.
You just have to ht edge and spine differently.
Blade form factor has heavy influence as well.
I've seen a lot of excellent fillet knives with excellent spring and excellent edge retention.
A Roselli I tested recently could bend like a leaf spring, yet had 63 HRc edge that needed ceramic or diamond sharpeners to resharpen.
It was a thin, long, wide blade. Don't know if it had had differential heat treat, but that could be a good guess given its peculiar properties.
 
In addition to all the problems with straightening the spring there is the fact that it was tempered to be a spring not a knife. Even if you had a dead straight spring and ground it cool you would have a poor knife.
 
Will Leavitt said:
I would think you'd develop massive stresses hammering steel into knife shapes cold, unless you're talking about filing or shaping on a grinder.
Click to expand...

I was assuming shaping would be done with a grinder. I'm not half as manly as it probably takes to beat cold steel into shape with a hammer.
 
AfterTFD said:
I was assuming shaping would be done with a grinder. I'm not half as manly as it probably takes to beat cold steel into shape with a hammer.
Click to expand...


Speaking from experience the money you'd save on steel would be more than offset by the number of belts and time you'll spend making most springs into a blade. Add the frustration of trying to get a good heat treat with an unknown steel and you'll find it's not the cheapest way at all. A quality piece of 10XX steel won't run you more than $20 shipped.

I've made blades out of leaf springs and coil springs, lots of time wasted straightening or hot cutting just to wind up with a blade that had inclusions and stress fractures.

Just my 2 cents from down here.
 
I've made various blades with old springs, most because the steel was available almost free and just behind my door, while the new one had to be bought far away from a factory that's open only during my office time... :grumpy:
Some were made from coil springs I used out of sentimental value (they were part of my Lancer Evo IX which was badly crashed by a moron coming up the opposite way in a blind curve far too fast). It's now fully restored to its original shine, but seemed a waste to throw away some almost new coil spring, anti-roll bar and axle.
p to now I made four knives without a problem, out of that coil spring, and many more will come.
Straightening and forging the steel has been part of the fun.
It's not been really much harder than forging some new K720 steel bar into certain shapes.
I also used worn out files.
Simple carbon steel is not very difficult to heat treat.
You don't have the scientific certainty you get with brand new steel but, then, I'm forging and heat treating with a coal forge, so "scientific" is not the keyword here ("medieval" is more like it! :D).
I also like to do differential hardening and differential tempering experimenting with various techniques, so I'm not interested in exact uniform hardening and tempering in an oven.
All the same, you can get really good knives out of it.
 
Get some 1084 or 1095 from Aldo, make your blade using this good, known, fresh straight steel, and when you're doneask if someone is willing to heat treat it. Heck if you put your town in your profile you might even find that there's a smith within easy driving distance who would invite you over so you could do your own heat treat under their supervision (Iowa is a big state to figure out if someone is next door in, I know, I got stuck for a week in Stewart for a week changing engines on my way to California)

good luck

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