Straighten During The Temper

Rick Marchand

Rick Marchand

Donkey on the Edge
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I had taken some pics today with intent to post a thread on how I straighten during the temper. I found it interesting that just before dinner, I received an email from a member asking about straightening.... coincidence? (I find that happens a lot on these forums.) Whenever I'm having a problem, someone usually is posting about the very same issue. I'd like to start by saying that proper normalization and pre heat treat practices would eliminate most of your warping issues. Tweaking during an interupted quench is very handy as well. Most of the makers I see use straightening jigs after the temper and over-bend enough for the blade to take a set. I'd like to tell you that my heat treat is so good that even the most exagerated bends spring back to shape... but I'm afraid that isn't so. Some blades work out well in a straightening jig and some snap. I have also clamped the tang in a vice and used a slotted 2x4 to bend and twist the blade back to true. The sad fact is that "warp happens" and our goal is to true the blade while keeping it in one piece. That is why I felt compelled to get this thread up, as I think it could prevent some broken/scrapped blades.

I brought this technique over from my Tool and Die days and scaled it down for knives. It is nothing new... just underestimated in its effectivenes, IMO. The basic concept is to clamp a bent/warped blade to something straight and perform a tempering cycle to lock it in. Sometime is takes a few tries but, hey... we are tempering in multiple cycles anyway, right?

This can be used for warps, twists and bows... you just have to get creative with your clamping. I don't know if certain steels aren't subject to this technique... I have personally used it on 1050/70/80/84/95, O1, 5160 and 52100.

Here are the ingredients...
IMG_0006-4.jpg~original


Warped to the left...
IMG_0008-5.jpg~original


Clamp it straight. If you end up needing to over-bend, shim between the file and blade. (I use spare change... lol). If the warp is slight enough, I will clamp it straight even before the first temper. You are putting very little stress on the blade during this process.
IMG_0010-7.jpg~original

IMG_0012-8.jpg~original


Run it through a tempering cycle. I usually water quench after each cycle to improve resistance to extreme cold embrittlement (something that Roman Landes recommends) I am not sure if that helps "lock in" the straightened blade or not. It doesn't hurt.
IMG_0011-10.jpg~original


The freshly straightened blade... I got it on the first shot.:thumbup: (I don't know why the picture makes it look a bit warped... believe me, it's straight as an arrow.)
IMG_0017-5.jpg~original


Thanks
Rick
 
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Just so I understand:

1) It comes out of the hardening quench with a little warp to it.
2) You clamp it to something straight (the big file), maybe shimming to over-compensate a little.
3) You temper it at the same temp and for the same time you'd temper it if it weren't warped.

...That's it!?

Jeez. I had a blade I took through the whole damned heat/beat/normalize/anneal/harden/temper process three times before it straightened the way I wanted it to. Good thing I haven't warped one since then...now that you've made correcting it look so simple.
 
It really is that simple..... I honestly haven't come across a blade that I couldn't straighten like this.

Knowing that a blade warped out of the quench isn't that big of a deal (and I can straighten it without risking a break) has reduced my stress levels 10fold. I still do everything necessary to prevent warp, in the first place, though.
 
Rick Marchand said:
It really is that simple..... I honestly haven't come across a blade that I couldn't straighten like this.

Knowing that a blade warped out of the quench isn't that big of a deal (and I can straighten it without risking a break) has reduced my stress levels 10fold. I still do everything necessary to prevent warp, in the first place, though.
Click to expand...

This is a huge tip, helps a great deal! Thank you Rick! :D
 
Well, Round 1 goes to the warping gods...it's not straight. I went about 30 minutes since it was already tempered twice. Trying again for longer this time.
 
How bad is the warp, Paul? You may have to shim it a bit to get a slight over-bend. I would go for atleast a good hour. Was that 30mins at tempering heat... or from insertion?
 
Good stuff. I do a lot of my straightening cold in a 3 point setup I built for my vise, this way seems just plain better. I can't wait to try it. Actually, I hope I never warp a blade again, but you know what I mean. Thanks.
 
Not sure how to quantify that, but it's moderately bad; if it doesn't work the second time I'll try the shim/overbend. Oh, I also rinsed it rapidly under the faucet afterwards since I didn't have access to anything large enough to quench it all at once.
 
Round 2 didn't work either. I'm trying an overbend with a shim this time...

Oops, missed your earlier question about time, Rick. It was probably a good 30 minutes at temp the first time, probably 45'ish the 2nd.
 
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Ughhh.... now I feel bad, Paul....

wait a tic...... 10:37pm - 11:17pm ??????.... and that is from the post of it failing... not to mention setup time for the next temper...

I don't think you are letting it get to proper heat, Paul. I have never gone under 2hrs. Give it a solid hour at temp, bro. I don't wanna see you posting before 1:00am!

Rick
 
I only slept about 4 hours last night, so I could be out of my mind on the time (but I thought I had set the timer after a few minutes warm up time!) Anyway, it's in there again with a penny as a shim this time, and I'm going to leave it in there until I go to bed.

Thanks again, Rick!
 
Don't thank me until it's straight... as of now, I'm just a big fat liar.
 
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You're not a liar if it works for you, and I'm probably doing it wrong. Anyway, I just appreciate your timely post and you answering my questions whether I have success or not.
 
Richard,
I started making kitchen knives recently and even though I heat treat at full thickness, I still get some warping.
I like to work in batches of three, and one batch I had 1 straight blade 1 warped left and 1 warped right. I clamped them together and tempered them for 2 hours, and then let them air cool along with the oven. I pulled them out later and all 3 were straight. I like your little C-clamps, I just use some bolts I had laying around, better grip with the C-clamps.

Del
 
Del,
Interesting that you clamp them together.... it reminds me of the way we dry harvested arrow shafts. We collect a dozen or so and bundle them tightly together... they come out straight as.. well... and arrow. Ha!
 
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