fixing a warped blade

A

andrew7978

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Mar 19, 2007
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As a beginning knife maker you guys have really helped me out. I just finished my first three blade, the smallest has an overall length of 5 inches and the biggest is 14. All made of 1095. Anyways I brought them to a metal shop to have them heat treated and go figure its the biggest blade that warps.

Is there anything I can do to fix this that won't ruin the temper?
Thanks.

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You can try heating the spine with a torch and bend it back as close to straight as possible. Can't guarantee the HT won't be effected on the edge though. Maybe put a soaking wet cloth on the edge to keep it under the tempering temperature?

Edit: Remember, the only part you care about staying hard is the edge, the spine can have some flex to it (i.e. differential hardening).
 
I would recommend redoing the HT. however if you just want to bend it back what I would do it put the edge in water and torch the spine. this will soften it up so you can bend it but also will keep your edge under 212' F. I strongly oppose this idea because it will leave stress in your blade permanently, and it may damage the integrity of the blade. I don't know a lot about this type of stress and its effect on the blade but I would re-HT it just to be safe.

-Josiah
 
This is the way I do it when necessary. I got this from a Bill Moran video, many years ago, and it works very well. I've never had a problem from it, but most will disagree with the practice. Put an inch, or a bit more of the point in the vise. Heat the spine in the area of the apex of the warp, being careful to not allow the heat to go to the edge. Or at least no heat beyond straw. Over flex the blade beyond straight a tad. Hold it there, and pour water over it. Then release the pressure, and see if you need to go again. With simple steels, once is often enough. Just don't go beyond your initial temper heat. You can also heat the entire blade for this, but I have found that unnecessary.
 
That may be on a Bill Moran video, and I don't mean the man any disrespect, but I doubt it is doing anything that tempering the steel to however hot you're getting it and simply bending it in a vice would do.

To shrink steel (to bend it with heat) you heat one side to very hot (it would ruin a blade) and that area trys to expand, but the cooler steel around it resists. As it gets hot its yield point drops and is forced to shrink as the cooler metal is resisting its expansion. Then you have to cool it quickly or the rest of the metal gets too hot and the effect is lost. Then, once it is all cool again, the area that was heated has shrunk down as it cooled to room temp, but it was squished down by surrounding metal while it was hot and expanded. Thick steel ship hulls are formed this way. The end result is the part draws towards where the heat was applied. But I don't think they're accomplishing that in the video and I don't this is the right technique for unwarping a blade.

I don't know how clear that was (pain meds for my back tonight). And by shrinking, I'm not suggesting it is actually more compact, but that the dimensions in the U and V directions are decreased while the thickness is slightly increased.

The best approach is to pull the blade from the quench medium around 500F and straighten it as it cools. It is only critical to quench quickly while it is passing the 900F mark, but down at the temps where martensite is forming you have all the time in the world and you can keep it straight as it finishes quench in air. It will be like taffy until it gets under 400. I have over corrected small problems because it is surprising how soft the steel is during quench.
 
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Big blades are always a pain, especially if you don't normalize before HT. This was suggested to me by Ray and some others, bring it up to tempering temp then carefully bend it straight wearing gloves.

There's also 2 other methods along those lines but don't require you to try to bend it IN your hands:
1. One is to use the ole rods in the vice trick, you have 2 rods vertically on one side and one centered vertically on the other, at tempering temps you put the blade with the apex of the bend on the single rod side and tighten the vice up. I have rods welded on some angle iron I put in the vice jaws, you can take 3 pieces of smaller diameter rod then cross drill the larger "bending" rods for a slip fit, kind of like a "T".

2. It's a Japanese technique using 2 notched boards with the notches near the ends. The notches need to a tight fit onto the blade. Put the blade in the notches and use the boards as levers to bend the blade straight.

All of these techniques require the PROPER SAFETY GEAR, I recommend face shield OVER saftey glasses, gloves and a leather apron at a minimum.
 
I would put it in the oven to 450 for 15 min and then try to straighten. The guy that tempered it should have straightened it when he tempered it. If you paid the guy get him to do it. I am not heat treating for a while, im gonna learn to walk before i run sorta speak. I have no problems cutting myself now, I dont need to add burns to my body , they hurt more lol
 
that WOULD have been an easy fix right after quinch, you have a window of "grace" to get things straight before the tempering cycle. Since everything is already "set up" I would re heat treat.

What ever you do dont give up yet, if you have no other means to get it heat treated locally (or on your own), PM or email me, I will do it for you.
 
It's not that easy Kelly. When it comes out of plate quench, it's brittle and prone to snap. Heating it up to 450 is not the same as straightening it as it is cooling through 450.

The big task is to keep it from warping through the first quench. There is a talent to that under any circumstances - and sometimes, it's darn near impossible. After that, it's anneal, normalize, stress relief and re heat treat - and that has about a 50% success ratio on a good day. :( Once one side has stretched - and the other compressed, perfect straight is a darn tough target.

Rob!
 
Rob im just throwing darts but i do know it should have been done or attempted to be done soon as it was qwenched. Thats why im letting you do it for me ide rather pay a few extra dollars and have it done right than to screw up 5 hours of work in 5 min. Lots of people talk the talk but only a few can chew gum and walk at the same time. The knives i got back from you after heat treating are profesional as can be being marked for rc hardness and unscratched from miss handleing
 
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