Be certain that you always give any warped blade one full temper cycle before you attempt to straighten on the SECOND cycle.

I agree with Karl. That's the only way I have had success getting a warp out.

Chris

Thanks, I'll do that next time.

The only other time I've had a warp I was quenching with tongs so after a few second in the quench I could quickly sight down the blade and fixed it during an interrupted quench, but with this being a folder I wanted to make sure the tongs didn't interfere with the quench on the tang/lock area. So I quenched it while hanging from a piece of bailing wire, which made it VERY difficult to see the warp until it was too late.

Hey Karl, nice write up in this months Blade! I love what you said about your philosophy about not testing for MS yet. I'm always awed by the willingness of other makers to help out the new guys.

So, I thought that the warp had occurred because of the way I had the blade propped up in the forge, but I don't think that was the case. I cut another chunk of from the same bar of 52100, rough cut out the blade profile on my band saw last night. Then at lunch today I ran over to Shane Taylor's shop and surface ground the new blade stock to thickness (.099") When I got home tonight I finished profiling the new blade, etc. Then I threw it on the disk grinder to clean it up after grinding the profile. Wouldn't you know it, the new blade already has a bow in it and I haven't even lit the forge yet.

I sighted down the bar it was cut from and there MIGHT be a tiny bow to it, but nothing like the way this short blade is bowed. So I have two questions:

1) What caused this? I know with wood if you plane off more wood from one side of a board than the other the stress/relief can cause the board to bow or twist. Is that what happened here with the bar stock? Did I surface grind too much from one side and not the other, or just remove enough material to all the existing bow become more pronounced? What's going on?

2) Where do I go from here. I plan to do 4 normalizing cycle before HT, should I clamp it between plates in the vice during the cool down stage of the first normalizing cycle? Try to bend it in a 3 point jig while it's cooling down from the first normalizing cycle? HT as is and try to fix the warp in the tempering stage?

this is the down side of surface grinders they don't make things flat, only parallel. my guess is that there was a slight strain in the piece that was either released by the grinding or increased by it. I think if you normalize and clamp it should come out. if not then the 3 point.

MP

I use a lot of 52100, and it can be "quirky" compared to other steels.

surface ground the new blade stock to thickness (.099")

In my opinion, thats a contributing factor. Any steel heat treated that thin increases the risk of serious warping. To piggyback on the surface grinder subject..... its not uncommon to have material that thin warp because of the surface grinder.....especially if the surface grinder is using a "stone" wheel. With the magnet pulling downward, and the wheel generating heat, its a recipe for warping when the magnet is released.

Something that caught my eye was in the first photo you posted...... that small chunk of brick with the blade leaned against......its a heatsink, that can't help but cause uneven heating, which in turn is another contributing factor to warping.

The way that I solve these types of problems is...... I simply do not heat treat anything less then .125" thick. Meaning that even if I want to end up with a blade of say .100", I leave it .125+" prior to heat treat, and then thin it down AFTER heat treat. As a general rule in my shop, anything less then .1875" (3/16") gets profiled and heat treated before any serious grinding on the blade takes place. Its not as difficult as it might sound, and it solves many of the issues you are experiencing.

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Something that caught my eye was in the first photo you posted...... that small chunk of brick with the blade leaned against......its a heatsink, that can't help but cause uneven heating, which in turn is another contributing factor to warping.

I wondered about that, which is why I included the picture. So should I...

A. Lay the blade flat on the hard firebrick forge bottom?

B. Lay the blade flat on a soft firebrick?

C. Drill a soft firebrick and add two rows of vertical pins to hold the blade standing on the spine, blade up?

D. Other suggestions?

All of those things you mentioned are options. Very often it comes down to just having to try various methods until you find what works best for YOU. Personally, I do the majority of my heat treating in the salt tank, but when I do use the forge, I generally have the tang end of a blade in a set of tongs, and don't place the blade on/against anything.....I just keep it suspended in the forge, moving it as required to get an even heat.

While I'm sure others have various methods, what I mentioned previously about thickness (everything that is intended to end up thinner then .125" gets heat treated before any grinding) and heat treating has saved me more grief then anything else I've tried.

Aside from what Ed has said, I will add this: Always try to heat it with the blade edge UP in oven. I would use a soft brick with grooves cut in just deep enough to hold the blade by the spine. Any time you introduce heat or extract heat unevenly, you are probably going to get warpage. Think about it, the brick has more mass and will take longer to heat. That means the side of the blade that is on the other side is heating faster expanding it at a faster rate with the net result of a warp. Karl has mentioned a way to fix a warp which works great. Leaning the blade side on the brick is the reverse process actually. Imparting a warp.