Heat treat HEAVY knife (leaf spring)

[Urthman]

Hi folks.  I just started playing around with knife-making with some truck leaf spring.
I think I have the gist on how to quench and heat-treat for a serviceable knife (time will tell).
A Marine friend of mine asked if I could make him a SUPER HEAVY EOD-style knife.  It would be about 1/4" thick, 11" long, blunted flat tip, and made to take serious abuse (prying car doors open and such).

In short:  It would be more of a heavy sharp prying tool than a 'knife'. 

Any advice on how to quench/heat treat some forged truck leaf spring to make a "knife-tool" that can handle this kind of abuse?

Thanks all!

[Steve Sells]

what part didnt you understand, do you want a knife or a pry bar?

[Urthman]

Hi Steve,

I guess to boil down my question for you pros:

If you were making a knife from leaf spring, would you temper it differently if you knew it would be used for Prying as much as Cutting?

[ThomasPowers]

Yes you would give it more of a spring temper; it will not hold an edge as well but be tough when abused by prying; or a differential hardening to have the edge hard but the back tough and realize the edge may crack under abuse.

[Steve Sells]

I will speak clearly so you can not fail to understand it is dangerous to use scrap steel.   Unless this is only a wall hanger, then don't worry about heat treat, make it and have fun.

If he expects to actually use this, you are going to get him killed. A soldier needs tools he can count on, because he is betting his life on his choice of tool.  You clearly do not have the knowledge and experience to make this.

Used steel is a crap shoot to safety and purpose.  No one has any idea how to heat treat unknown steel composition.
A pry bar needs to be very forgiving to flex and take a beating with out breaking and possibly killing the user.  A knife needs to be hard enough to hold an edge so it can actually cut something and still hold up,  failure here means a blade section may end up in the user.  If you think a cut in the shop is a pain, try having one in the middle off no where with some one shooting at you.  Having both flex fro a pry bar and a hard cutting edge is not possible in a knife shaped object even if you used a good steel.

[Urthman]

Thanks for speaking plainly. Sorry I did not do more of the same in my first post.

This knife will be for 'kicks' on the homefront.  The real versions of this knife/tool are $900 for a reason, and that is well understood by both of us.

This one, I plan to make, beat the heck out of, and give it to him if he wants to play with it.  (it's a pry bar that can probably cut rope)

Thanks!

[Steve Sells]

that I agree is a safe way to do it,  make a pry bar, with  a "gut hook" and maybe a small edge like an axe would have,  forget anything like a real knife, and you can  do it. but use good steel.  5160 or so is a good place to start,  $2.50 a Lb isnt really  too much.

[Charles R. Stevens]

i just gave my "entry tool" to a cop friend of mine, the tip was dead flat with an axe like grind, if one hit the hilt it would cut clean threw the wooden dore trim and get behind the doore. The edge was simularly shaped, the temper was like a good axe, as one could maintain it with a fine mill cut file (just barely) somthing that big and heavy is a knife shaped axe

[Urthman]

"knife shaped axe" (K.S.A.?)

If I actually make it, I think you just named it for me...

[Frosty]

He wants a Halligan not a toy. A man with a halligan don't need no steenkeen: axe, pry bar, knife, nor other close combat weapon.

Frosty The Lucky.

[ThomasPowers]

might look up a smachet/smatchet for a previous tried military grade knife

Edited July 21, 2015 by ThomasPowers

[Dogsoldat]

Had to look up a Halligan,  quite the interesting bit of kit...

 

[SnailForge]

Thanks for speaking plainly. Sorry I did not do more of the same in my first post.

This knife will be for 'kicks' on the homefront.  The real versions of this knife/tool are $900 for a reason, and that is well understood by both of us.

This one, I plan to make, beat the heck out of, and give it to him if he wants to play with it.  (it's a pry bar that can probably cut rope)

Thanks!

Even so, I would NEVER use scrap steel for anything that will be subjected to severe impact or high tension. Even if you just give it away and they use it for 'kicks', it is just too dangerous. Truck leaf spring can have hairline cracks internally or fatigue places. If they try to force open a door just for laughs, and the bar breaks under tension, someone can lose an eye or worse.

It is cool that you want to give it away, and if you want to do that, start with known good steel that you know how to heat treat. For a knife it wouldn't matter, for an impact tool or prying tool it does.

Of the steel I have worked with, I would probably choose 52100 for the usage you described.

[Urthman]

That's good advice.  A new chunk of good steel is not terribly expensive, and probably worth the peace of mind.

Thanks guys.

 

[jmccustomknives]

Look into edge quenching or the soft back draw methods.  I feel the latter gives a little more strength but done properly either method will make a very tough knife with good edge holding.  I use these methods on all my rough use/big knives. 

[Steve Sells]

JMC is forgetting about the pry bar aspect, which needs full hardening, not an edge quench....

Edited July 26, 2015 by Steve Sells

[Nobody Special]

Good grief. I knew about the fireman's adze, but not the halligan. S'right though. Every knife or knife-ish object I've every seriously pried with has broken sooner or later. And once when it did, cut the artery in my left thumb, spurt....spurt...spurt....and counted myself lucky.