HELP!! Fixing warped blades.

C

CWknife

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Dec 27, 2015
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Hey guys I just got back after a long 4 month stay away from my home to return to my knife project. I heat treated my 1095 blank successfully but it was dark outside so when I finally saw it in the day light it is warped to the right, not a lot but noticeable. My question is what is the best way to straighten the blank? This is my first knife and I do have access to a fairly well equipped shop. Any help will be greatly appreciated.
 
Straighten it when you do the first temper. Clamp it to a thick bar of straight steel then temper it in the oven and it will come out straight. I only get this to work 100% on the first temper, after the first temper it becomes much harder to straighten in the heat treating as the blade will have to be clamped to the steel bar but shims used to over bend it in the opposite direction.
 
A hardened and tempered blade should only attempt straightening if heated to 400 F [or up to final temper temperature if higher ]
Another way is to straighten by quenching till you get below critical , then straighten before reaching Ms temperature, then you may air cool or water cool.
The third way is to do a sub-critical anneal [ 1200 F for two hours ] after macining, straighten then HT.
 
JTknives said:
Straighten it when you do the first temper. Clamp it to a thick bar of straight steel then temper it in the oven and it will come out straight. I only get this to work 100% on the first temper, after the first temper it becomes much harder to straighten in the heat treating as the blade will have to be clamped to the steel bar but shims used to over bend it in the opposite direction.
Click to expand...

So you're clamping before any tempering? No risk of breakage that way?
 
Nope, as long as your blade is not the shape of a banana.
 
JT, that's really interesting. Are you clamping your blades straight before they have cooled down to MF, or at least before it's come all the way down to room temp?

I'd personally be a bit afraid to clamp a warped blade, even simply clamped straight without any counter bend, if it had already completely cooled down.

Either way, clamping it straight between two bars before it reaches MF, then allowing it to finish cooling in them, and then keeping them clamped while going through its first temper cycle seems like it could be a good (and extra safe ;) ) way to go about.

I'll have to try this on my next warp, as the current blade I working on, after I had tempered it once went through probably another 5 temper cycles while clamped with a counter bend at the apex of the warp, and it did NOT want to straighten out at all. It pretty much stayed the same even though I continued increasing the counter bend after each cycle.

So I ended up bringing it back up to about 415F once more, but this time I took it out while it was hot and used a "three-point" straightening jig in a vice, which was finally what got it to straighten out (enough). It really took a surprising amount of counter bending to get it to straighten out, though!


~Paul
My YT Channel Lsubslimed
... (It's been a few years since my last upload)
 
after the first tempering cycle, i lay the blade on a flat surface and gauge the size of the warp with nickels, dimes or quarter coins. whatever coin fits, i counterbend with two of the same coins on a piece of angle iron and c-clamp. ( counterbend twice the size of the warp) and retemper. works 98% of the time. rarely it requires a third tempering/bending.
 
Like I said if you clamp it straight for the first temper you don't have to counter bend it on the second temper becaus it comes out straight. It's like sneaking up on it and straightening it befor it knows what happening. But if you temper first and then try to straighten it on the second temper it is expecting you and you have a fight on your hands.
 
You have an entertaining way of explaining that, JT! I usually do like John does, more or less, if I have a warp that got past my gloved hands before Ms. Often it does take some messing around... I'll try clamping straight after quench before temper and see how that works.
 
JTknives said:
Like I said if you clamp it straight for the first temper you don't have to counter bend it on the second temper becaus it comes out straight. It's like sneaking up on it and straightening it befor it knows what happening. But if you temper first and then try to straighten it on the second temper it is expecting you and you have a fight on your hands.
Click to expand...

I used your method with a fairly warped hatchet, and boy did it work great. Straight as an arrow.
 
If it's not too thick you can use a bead blaster if you have access to one. I have done this on cpm154 at 61rc numerous times without any issues. Just blast a section vertically along the bend on the concave side. This essentially makes a lot of tiny peens and stretches the surface on the concave side and pushes the blade back straight.
 
I've been doing it JT's way for some time now. At first I thought you couldn't remove warp without a counterbend, and I was afraid to counterbend before the first temper, but I'd say 75% of the blades I've simply clamped straight during the first temper have come out of the first temper straight, and the other 25% that needed more attention were better than they went in, so I give them a slight counterbend in the second temper.

Has made my life a lot easier since I've had a rash of warping in oil quenching and interrupted quenching clay clad blades experimenting with hamon creation.
 
JTknives said:
Like I said if you clamp it straight for the first temper you don't have to counter bend it on the second temper becaus it comes out straight. It's like sneaking up on it and straightening it befor it knows what happening. But if you temper first and then try to straighten it on the second temper it is expecting you and you have a fight on your hands.
Click to expand...

I think in the first temper there's enough conversion going on that retaining the clamped form is what the steel "wants" to do. By the second temper there's so little activity that a counterbend becomes necessary.
 
Somebody already linked to it but I have been straightening in the temper for a while with good results. I snap temper at 375F for an hour first, then clamp up and straighten on the next. While I like JT's analogy to "sneaking up" on the steel(and will probably use it), it really doesn't explain what is actually happening. We are essentially creating stress and relieving it. As opposed to the method of fighting stress with stress... as in using a 3-point jig or the like. If you temper a blade that has been straightened in a vice, it will most likely take a warp again, where a straighten by temper blade will most likely not. I have learned that going back to straighten at a lower temperature is not as effective. 10F or so goes a long way. Like I said, with a warped blade I start with a 375F snap temper, then 400-425F clamped temper, with a follow up at the same temperature, unclamped. I always repeat the last temperature to temper out any RA that may have converted at the preceding cycle.

I do not clamp prior to that first snap temper, ever. There is so much stress in a freshly hardened blade. Too much to risk it, IMO.

Here is the link, again. http://www.bladeforums.com/forums/showthread.php/838681-Straighten-During-The-Temper

I also use the heck out of Stacy's recommendation to clamp up a blade with aluminum plates after an interrupted quench, while it goes from Ms to Mf.:thumbup:


Rick
 
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you guys are clamping before the first temper ? wow, lots of balls lol. i did not think the metal could flex at all when fully hardened without snapping. is it still hot from the quench never having come down to room temp when you put it in the tempering oven ?
 
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