I'm kinda new to this site, though I recognise many of the members here.
I have posted this thread on another forum with a surprisingly good response. Frankly, I didn't think it was anything new but I guess it is one of those "smack... why haven't I been doing that?" type of thing. I did a search and found nothing on what I have to present but I am new here... so maybe this isn't even the right place to post this.
STRAIGHTENING DURING THE TEMPER CYCLE has allowed me to sleep easier. I am no longer haunted by the TINK of snapping blades in a straightening vice.
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 common practice, 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 warped blade to something straight and perform a tempering cycle to lock it in. Sometimes, 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(stainless in particular) 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...
Warped to the left...
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.
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.
The freshly straightened blade... I got it on the first shot. (I don't know why the picture makes it look a bit warped... believe me, it's straight as an arrow.)