Jump to content

Blade Straightening


Eric C

Recommended Posts

Okay, here we go again. I've forged out a few knives, but never finished one. One of the main reasons is that before I ever get to heat treat, I sight down the spine of the blade and it is always curved one way or the other. I try and try to hammer it straight, but it seems that I always get that blasted curve! So, is there an easy way to tell what I'm doing wrong?

I've seen jigs that will straighten blades and I've thought of making one. I mentioned it to a guy who teaches at a school here in NC (several hours away from me) and he said, "Nah, hammer it out." I never got an explanation from him on how to do it, so I'm back to square one. I try to be careful to strike the same number of blows on each side of the blade. So, is this too vague, or is there help for me?

Resident knife-maker-wannabe

Link to comment
Share on other sites

Okay, here we go again. I've forged out a few knives, but never finished one. One of the main reasons is that before I ever get to heat treat, I sight down the spine of the blade and it is always curved one way or the other. I try and try to hammer it straight, but it seems that I always get that blasted curve! So, is there an easy way to tell what I'm doing wrong?

I've seen jigs that will straighten blades and I've thought of making one. I mentioned it to a guy who teaches at a school here in NC (several hours away from me) and he said, "Nah, hammer it out." I never got an explanation from him on how to do it, so I'm back to square one. I try to be careful to strike the same number of blows on each side of the blade. So, is this too vague, or is there help for me?

 

Im i right in thinking we are talking a knife not a japanese blade ? if so the only way i know is heat it up then hammer it on a FLAT anvil with a chunk of wood Flat under it doing it cold is not a good way to do it try to get the line in before you finnish forging the blade thats the best way because cold steel will not respond as good as hot steel and is more liable to develop stress cracks working hot is always preferd you could try the bridge method too a chunk of wood under the tang and the tip just outsied the curve area then with the curve upward heat with a torch till red then hit but not to heavy till the curve flattens out to you satisfaction if you go to far then your back to square one when you have it right or within reason then finnish of on the long chunk of wood (((( you are bacicly hammering one side more than the other maybe just a little harder than you realise so streching one side more than the other it all boils down to hammer controle mate it takes a while to get it right we have all been there and stressed over it ,you can usualy tell as you hammer you will see the blade curve one way now's the time to do the other side to bring it back

 

I hope this is more help than the smith you asked mate

 

cheers terry Aust

Terence.........(today started off perfect now --- watch sombody come and stuff it up ]

 

if it aint broke dont fix it

Link to comment
Share on other sites

You didn't talk about how you heat treat your blades. One thing that can cause a warp in a blade is moving the blade from side to side in your quench medium. What you want to do is go into the quench, edge down, and hold it there. If you need or want to lift it out, lift it straight up. Don't move from side to side or swirl the blade.

 

You can straighten a blade right after the quench, if you can catch it while it still around 400-600 degrees. You want to move fast but you can tweak it with vice or tap it into line on the anvil, then go back into the quench to bring it down to cold.

 

This is one of those things that some time with a more experienced smith would help. If you can find someone, ask if you can bring a blade, ready to HT, to their shop and HT it there. Seeing is better than hearing.

 

Hope this helps,

 

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

Link to comment
Share on other sites

ok .. from what i understand you are saying ..

after forging out a blade ... you look down the spine and find that the blade is bent one way or another ..

and you want to know what you are doing wrong?

going on that assumption and not that you are talking about a forged curve of the blade .. i say;

 

well .. there could be many different reasons..

but essentially your teacher person is right .. its best to heat it up and hammer it flat..

but .. if you dont have a flat surface to hammer on, you might find that you are putting a curve in that way ..

or you might be using too small of an anvil surface.. try laying it along the anvil .. not across it ..

if you have a too heavy hammer .. you might find thats the culprit ..

or you might find that you are hitting it too hard to whats needed ..

umm .. there are just lots of things that could come into it.

 

essentially the metal will move, normally, where you tell it to go.

if you are finding that there is a bit of a curve being forged into your blade .. it should be a very hard thing to just tap it out ..

but also .. it depends on what kind of degree of bend we are talking about too ..

if its massive .. then thats one thing ..

but if its only slight, then you might be worrying for nothing .. and could possibly grind it out during your knife making process until you figured out what the real reason is for the wonkiness (technical term) to begin with.

 

do you have some pictures?

can you let us know what you are using to forge out your blades?

info info info .. and we can reassess.

^_^

deeDWF4.jpg

Link to comment
Share on other sites

To add to what Dee already asked/said are you holding the blade flat on the anvil. If your hand/tongs are slightly raised then you'll end up getting that curve in the blade. Hold the blade and lightly tap it flat check your progress frequently. I "one more heat" myself to death when doing the final straightening. One other thing to think about is that if you have a thick spot in the spine it could look warped even though it's not.

Adlai

Klatu Baratta Necktie!

 

Macabee Knives

Link to comment
Share on other sites

The blade that I am closest to finishing is a sgian dubh forged from a file. Like the others that I have attempted, it is bent. Bent would have been a better word than "curved." Thanks for all of the advice so far. I'll try to get some pics. I don't know if it will show up on film. But I'll try to get some "before" and hopefully some "after" shots.

As for what I am using to forge them out, I have been using a 2 pound hammer and a Harbor Freight 88 pound anvil (I know, I could use a real anvil). I have a lighter ball peened hammer that may work better, what do ya think?

Another thing that crossed my mind is not just number of blows per side, but placement of blows. If I am not spacing them close to the same from one side to the other, could that also cause it?

Geoff, on most of the blades, I haven't even gotten to HT yet, but I'll remember your advice for when I do get there.

Resident knife-maker-wannabe

Link to comment
Share on other sites

How many time have I seen this question? Try how many times have I asked this question. On my last blade I noticed a slight curve while it was in it's annealed state. I just padded the blade with a leahter strip, clamped it in my vice, and just pushed hard against the curve to get it out. Another idea is to take a plate of steel about the size of an anvil face and grind a very slight sway in the surface. Then lay it one the anvil, lay the blade on it and see if you can tap it out with a wooden mallet. The end of a log with a slight dip in it can be used too. First be certain that there is a curve. Lay the blade on a flat surface that has been comfirmed by a level. See if there is a space between the blade and the surface or if the blade rocks a bit. Turn the blade to the other side and check again. If the blade is seriously crooked, you might just have to heat it up in the forge, straighten it, then re-heat treat it.

 

Doug Lester

HELP...I'm a twenty year old trapped in the body of an old man!!!

Link to comment
Share on other sites

Eric,

When I was working as a farrier's assistant, I was told (and rightly so) that you can't hammer steel up, in other words when you are forging out a blade, lay it on the avil face (incedentily I use a harbor freight 100# russian anvil, too soft but it works ;) )

and sight under the blade, any where you see daylight (assuming the blade doesn't have an intageral bloster or somthing like that) and that is more or less where to hit it. That is where the saying "beat the livin' daylight out of it" came from. Also, if check and see if your forge is heating the blade evenly, or you can flip the blade over while it is heating.

For what it's worth,

Ben

Ben Potter Bladesmith

 

 

It's not that I would trade my lot

Or any other man's,

Nor that I will be ashamed

Of my work torn hands-

 

For I have chosen the path I tread

Knowing it would be steep,

And I will take the joys thereof

And the consequences reap.

Link to comment
Share on other sites

Sorry, I misunderstood the question. Once you've done the heavy forging, sight down the blade and mark one spot where you've got a problem (soapstone works well). Take a light heat and choke up on the hammer (or move to a lighter one). Lay the blade with the high spot up on the anvil and give a couple of light taps and check it. If it moves too much to the other side, lighten up your blow and try again from the new high side.

 

You want a just barely red heat, you are not trying to move metal, just take the kinks out. This is a fussy process, a little here, a little there. It sometimes takes almost as much time to straighten out a blade as to forge it. I use the end of every heat to take the kinks out, and often I will take a red heat just to de-kink a blade while forging, this saves you some time at the end. But you will still have to do some straightening at the end.

 

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

Link to comment
Share on other sites

How many time have I seen this question? Try how many times have I asked this question.

Doug Lester

 

Hehehe. I tried to get a couple of pics of the blade, but it was too dark. They didn't come out very good. So, I'll try again tomorrow. Hopefully I'll get to fire up the forge for a while Friday afternoon and see about getting this thing straight.

Thanks for all of the advice. I'll just have to be patient with it and keep trying.

Resident knife-maker-wannabe

Link to comment
Share on other sites

  • 3 weeks later...

I DID IT!!! Saturday I went to a local knife-maker's house and got some tips for grinding knives. It didn't take as long at his house as I thought, so I came home and forged a couple of knives. I ran out of daylight, so I annealed the knives and put them into the wood ash bin along with two other knives that I was annealing. Sunday I pulled all four out and every one of them was bent. So I did what I could to straighten them, reheated to critical heat and stuck them back into the ash. Today when I got home, I pulled them out of the bin, brushed them off and checked them out. Three of the four are straight!

So, hopefully I'll be posting a couple of finished knives soon!

Resident knife-maker-wannabe

Link to comment
Share on other sites

Hrmmm...you say the blades went into the annealing bin straight, and came out bent? You aren't by any chance using leaf springs, are you? (just a thought). I assumed you were talking about bending during the forging process, but this sounds like it might be something different to me. Hopefully someone might be able to shed some more light on this with this new info, I'm still a newb at this myself and the only thing I could think of is that the steel may be 'remembering' a previous shape, as I've read here happens sometimes. Otherwise, feel free to ignore me. :)

 

cheers,

/steve

Link to comment
Share on other sites

No, I imagine they were bent when I put them in, but it had gotten dark outside and daylight is my only light besides the forge itself, so I couldn't see if they were straight or not. BUT your suggestion actually does bring up another problem that I have heard of before. If someone more knowlegable than myself would like to discuss this problem, ie straight blades into the ash pot and bent blades coming out, please feel free. All of us newbies would certainly benefit from such a discussion.

BTW, the blades that I forged were from 12" files. When I find a computer with a usb port, I'll try to post pics. (My surviving computer is a dinosour)

Resident knife-maker-wannabe

Link to comment
Share on other sites

The only two things I can imagine that would result in a straight blade coming out bent are

 

a.) the ash is damp, moreso on one side of the bucket, which cools one side of the blade faster than the other resulting in warpage, or

 

b.) you're getting the blades WAY too hot and bending them when you jam 'em into the ash bucket.

 

Situation "a" above is extremely unlikely to happen more than once. I've done "b" myself. :rolleyes: Is your forge located somewhere you can see the transformation in the steel at critical? Too much light, whether ambient or from the forge, will wash out the shadows. If you've never observed the transformation on a rising heat, you may be shocked to the core of your being at how relatively cool you think the steel is when it happens. In daylight, by the time the steel is hot enough to show color you've overshot by a hundred degrees or more. In a dimly lit room, what looks black in sunlight can be a full red. :blink: The transition takes place in that temperature range.

Link to comment
Share on other sites

"b" sounds like something I would do just prior to much screaming and calling myself all sorts of obnoxious names. Then I would have to explain to my two young children why they shouldn't say those things. :rolleyes:

My forge is located at the back of an old car shed. It's usually pretty dark back there, compared to direct sunlight.

As for color ranges, in my job, when welding a bandsaw blade, there seems to be a disagreement between various filers over whether to have more light or less light focused on the spot of the weld when you normalize the weld. Some argue to have less light and bring the welded spot up to a very dull red. Others say to have brighter light on it and make it grey with a shadow chasing the feather of your oxy-acetyline torch.

Resident knife-maker-wannabe

Link to comment
Share on other sites

As for color ranges, in my job, when welding a bandsaw blade, there seems to be a disagreement between various filers over whether to have more light or less light focused on the spot of the weld when you normalize the weld. Some argue to have less light and bring the welded spot up to a very dull red. Others say to have brighter light on it and make it grey with a shadow chasing the feather of your oxy-acetyline torch.

 

 

For simple steels like your files, the transition as seen in dim light is as follows: The steel is brought slowly up to a low red in the forge with no additional fuel or air added. as the steel enters the critical range, you'll see shadows start to swirl inside the steel, followed by a brighter line that chases the shadows up the blade. When the whole part you want hardened (or normalized or annealed) has been freed of shadows, the transition is complete. Very cool to watch. It happens in reverse on the way back down, too.

Link to comment
Share on other sites

Hi Alan,

 

Thanks for your thoughts on this. When speaking of the shadows, you're talking about the decalescence/recalescence phenomenon, correct? The way I've heard it explained was a little different, but your explanation is a lot easier to match up with actually *doing* it. Cheers.

 

/steve

Link to comment
Share on other sites

Hi Alan,

 

Thanks for your thoughts on this. When speaking of the shadows, you're talking about the decalescence/recalescence phenomenon, correct? The way I've heard it explained was a little different, but your explanation is a lot easier to match up with actually *doing* it. Cheers.

 

/steve

 

 

Yep, that's it! The illustrious Dr. Batson told it the way I explained it above at a class I took from him. The neat thing about using this phenomenon instead of the ol' magnet trick is that this works with any steel, even those that have a critical point substantially higher than non-magnetic, such as 5160. For instance, all steels go non-magnetic at about 1450 degrees F. To get the most bang out of low alloys like L6 and 5160, however, you need to get 'em a little hotter. Decalescence only happens when the structure of the steel is ready to be hardened, be this at 1425F or 1550F.

 

edited to add: Like many things I blather on about, remember I never said it was easy to do! ;)

Edited by Alan Longmire
Link to comment
Share on other sites

Should you place the blade on the fire with the edge down, or with the edge up? I have placed it edge up before and things seemed to work out pretty good. But at this stage of the game for me, when things go right, it's pretty much beginner's luck. I'm looking to turning it into acquired skill instead. :D

Resident knife-maker-wannabe

Link to comment
Share on other sites

Edge up if I can, flat if I can't help it. :lol:

 

I work in coal/coke, so I build a cave fire and use the cave for heat. The big thing is to turn off the air while you're heating the blade, unless you don't have enough residual heat.

Link to comment
Share on other sites

CAVE FIRE! I'll have to remember that. Of course, I'll have to work on my skills at building one. I've "heard" plenty about it, I just haven't tried it myself. I usually use an open fire for whatever I do in the forge.

Resident knife-maker-wannabe

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...