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Elmarginalo

Straightening longer blades

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Hi guys,

 

I'm attempting to make my first larger knife (chopping knife for in my garden) in the forge.

I'm having a bit of trouble getting this straight:

- What we learn at forging school to straighten something is to check it when it's cold.  We look at the axis and give it a tap here and there cold to get the axis nice and straight.  now mind you this is on plain iron, not on steel.  Are you allowed to hit it cold or will I introduce micro cracks in it?

- If I try and straighten it out hot, it's not really going that well either. I have a bend in 1 direction, tap it and I introduce another warp... sometimes a bit better, sometimes it's even worse then before.. 

So how do you guys straighten it?  temperature lower perhaps? like darker shade of red to straighten it instead of bright red/yellow? 

Any other tips?

THanks in advance!!!

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It really depends on the type of steel you are using, when it comes to hitting it cold.  I use 1095, and don't have any trouble with hitting it cold.  I believe you only have to worry about micro cracks in alloyed steel, that has alot of chromium or manganese.  Not 100% on that though.

I usually straighten at a black heat, just below red.  I try to straighten and true the shape I am working on at the end of each heat, that way the over all shape won't get away from you. 

Lets say I am working on forging the end of a piece of flat bar into a point for the knife.  I'll pull it out at yellow/orange and forge the point with heavy even blows.  As the metal cools into the red I lessen the strength of each hit, making them faster and lighter.  I do this in order to planish the piece, removing any hammer marks from missed blows.  Then I eyeball it for straightness, and give it a few more light hits as it cools into a black heat in order to make it relatively straight.  Back in the fire it goes.

I will do some tweaking in a vice as well.  You want to have the part that needs to bend just outside of the vice jaws, use a pair of tongs with a good firm grip for leverage and bend just a hair past straight.  You'll get the hang of it.

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There is a difference between hitting a normalized, preferably Anneal piece of tool steel and an heat treated one. Wouldn't recommend the latter. 

Straighting is where one comes to appreciate a sway backed anvil, as it is near impossible to straiten a piece of cold steel on a flat anvil. One can bend a "U" or a long oval and then flatten the stock (1/4" on edge isn't bad, I do it all the time, but 1/8" sucks) this gives you a bending saddle that you can use, the oval works very well as you have a long side for warped and a short side for kinked. 

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This is what I use. Non-marring copper rod. Works pretty good, but as others have said, ya gotta be real careful.

image.jpg

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The copper is a great idea.

 

I straighten on a flat anvil at a red heat. and then again at normalising temps. or by bending in open vice jaws (gently). its often a case of a little bit one way then a little bit the other and on and on.

I try not to hit any carbon steel cold.

there are lots of different ways to straighten blades.

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Some times clamping the blade between two pieces of "C" channel hot works, be aware that the blade will "quench" some what so heat black heat before tweaking with your vice jig.

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I use two sloitted sticks of Ask and tweakl/torque them in..sometimes i need the Cu block..sometimes just the torque does it, depends upon how bad it is warped or worse yet twisted.. (This is in book IV BTW)

JPH

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Thanks a lot for all the ideas and tips guys!

Managed to get it nice and straight, now I need to clean up a little more and grind in the bevels

 

Steel is O1 btw.

 

2015-03-21 20.59.24.jpg

Edited by Elmarginalo

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Looking good! Can't wait to see what it becomes.

I would not recommend O1 for anything larger than that puppy, it's best for small/medium knives IMO

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I'll post some more pictures when I get further ;-)

Sorry for the stupid questions but why is O1 no good for larger knives? 

Is it cause of the very high carbon content?  I figured if I temper it back enough & temper the spine, it would be ok.  Any steels you would recommend?

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