How to straighten bent blades?

I have come across bent blades in my longer chef knives, I currently have a 300 mm blade that is bent at the tip, but it's a slight bent, only visible when placed on a flat glass surface. Still it hinders cutting performance and it will be a long process of slowly bending it with a hand towel and pressure. I was told to do it slowly over a long period to prevent fracture.
I'm almost thinking about buying a new one, but at 500 for an almost decent one... I'll try my hand at bending lol
 
Again, time at room temperature has absolutely nothing to do with bending steel!
Just over-bend it in the other direction. HOW LONG you bend it doesn't matter at all.
Now you have been told the facts.
 
davek14, thanks for the info. I'm definitely up for a set (or two) whenever you get a chance to get back to 'em. Glad things are going well with the arm. Take care of it, and again I wish you a speedy and uneventful recovery. :thumbup::cool:
 
bdmicarta said:
Blade steel at operating hardness is not very ductile. IOW you can bend mild steel pretty far back and forth and eventually it will break because it is very ductile. But hardened steel will not have that ductility. Bend it a little bit one way, then bend it a little bit back the other way and it fractures. I was actually demonstrating the high strength of Post Tension reinforcing wire in my office by breaking pieces, while a similar diameter piece of coathanger wire would bend back and forth numerous times. But if the OP's blade has a bend in it, it has already taken a set. IOW it is reached its yield stress and undergone plastic deformation.
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I'm sure in an absolute sense you're right. It's probably a matter of how severe the bend is. I say this because I've straightened a good number of blades. Most had fairly mild bends. Some easily noticeable but not bad. All of those were fairly straightened without any breaks. I've only broken one REALLY badly bent blade. Again, I think this is a matter of how bent and how many bends. For typical stuff, it's no big deal to straighten blades. In my limited experience. Murray Carter seems pretty adept at it, and he's where I got the idea and inspiration to try it myself. :)

Brian.
 
I have been looking around the net for info on whether time elapsed while bent in the opposite direction would have an effect on straightening. No luck there. I would love to find technical stuff on that.

I know that in metal fabrication/machine shops straightening is just another operation. Tribal knowledge is "just leave it for a few minutes and that will help". This is unhardened steel generally and tribal knowledge is not always correct.

I have been off work with wimpy hand strength for a week and have straightened two blades. I have my impressions which also may not be accurate, but for what they're worth.

Leaving Svord mini-peasant blades overbent against the existing bend for a period of time has little if any effect on it "taking" the bend *but*... It seems that you can overbend till it takes some strength to continue and you are fearing the blade breaking, then leave overnight and it takes some more overbend pretty easily. Thus you can do more of an overbend with less fear of breakage.

I really don't know. YMMV.
 
The blade shall look like this ll = two parallel sides. When a blade is bended, one side of the blade is longer then the the other side, the metal have been stretched. The blade look like this: )) the side to the right is the longer side.

The only way I know about is to overstretch the blade in the other direction, meaning this: (( and to make this under good control. Whats happen is that I must make the shorter side equal long as the longer side so that the blade again! lok like this: ll

I use a vice and three small pices of wood and use the vice to control the "overbend" I must do. I bend a little and then I check out the result. I bend a second time and use a little more pressure - and check that out - and so on.

I use a steel liner and good light to se the result. The steel Linder stand upp on its long side on the edge and the light is behind. When I have succéd - i cannnot se any light between the blade and the liner.

Thomas
 
You can look around the net, but I make thousands of leaf springs, and I repair knives.
You can pretty much take my advice to the bank. I don't post just to be posting, but to help people.
 
Bill DeShivs said:
You can look around the net, but I make thousands of leaf springs, and I repair knives.
You can pretty much take my advice to the bank. I don't post just to be posting, but to help people.
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What Bill said!
On production stainless knives I have some success straighten cold use a a 2 x 4 I have made kerf cuts into with a saw to hold the blade in while I push slightly the other direction if the bend is very slight, sometimes the bend will come back on its own lol.

I do the same process to re-due the Set on scissors after sharpening, they can break too! lol

Stay safe and focused when doing this kind of work and anything else to do with knives. Skin & bones loses every time against edged steel!:eek:
 
Bill DeShivs said:
You can look around the net, but I make thousands of leaf springs, and I repair knives.
You can pretty much take my advice to the bank. I don't post just to be posting, but to help people.
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Sorry, I did not mean to seem as if I was arguing. I was actually surprised that time clamped had little effect on taking the set. As far as the metal "relaxing" a bit and taking more of an overbend, that could have been the c-clamp or another part of my set-up relaxing. Just posting my experience for what it was worth.
 
Making leaf springs for automatics has taught me much about bending steel!
 
In stamping sheet metal, hydraulic presses sometimes have an advantage over mechanical because they can slow down, form more slowly and dwell at bottom. This seems to help a little with springback. But we are talking hundreds or even thousands of tons of pressure, and dwell of a second or two. And metal that is thinner than knives. So I tend to believe Bill's advice.
 
Sorry to be necro posting but I read through this thread before attempting to straighten a blade on a Bear MGC USA medium stockman and wanted to add some info.

It must have something to do with how well the steel is treated because this blade I straightened this morning was totally easy.
Very pliable.
I just clamped the bade in a small vise above the bend and very easily bent it back into shape with some one handed pressure on the handle.
 
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