Lesson learned

[MilwaukeeJon]

Relatively new to knife making and made a brilliant boo-boo yesterday, stupidly trying to straighten a quenched blade prior to tempering. The result was not good but I was not upset because frankly I needed to learn this lesson about the brittleness of hardened (5160) steel. 

 

And on the good side the broken bits were still usable. Tempered them and then made a marking knife and a kitchen chopper. 

 

 

[Joël Mercier]

The exact same thing happened to me on my first. It may be too late but you can take this "opportunity" to examine your grain size. See if you had the right temp before quenching. 

[MilwaukeeJon]

Well I did look closely although didn’t really know what to look for. Looked rather evenly granular to my eye. 

[Joël Mercier]

It should have the texture of fine sandpaper. Something like 400 grit and up. If you could actually see the grain, it was too big. Here's an example of a good grain size

[MilwaukeeJon]

That’s about what it was.

[Joël Mercier]

Excellent! It's hard to nail HT the first time.

[MilwaukeeJon]

Not the first time. I’ve done a number of heat treated knives and about a dozen herb choppers, and ten or so hammers as well. HT still is a wondrous mystery!

[Stormcrow]

You have a narrow window of about thirty seconds during which you can straighten a warped blade out of the quench using gloved hands, quench plates, etc.  I don't like to do it, but sometimes it's the only way.  On my episode of Forged in Fire, after about three times of re-heat treating my katzbalger blade to try to fix warps, I finally had to do it.  Worked just fine.

[lyuv]

Learned a nice trick (here, of course...): Use the 3 points system, and apply pressure gradualy at tempering temperature.

I tighten the c clamp a little every 10-20 minutes, untill there is a slight "over-bend". Let it cool enough to hold before releasing the pressure.

Worked for me several times.

Always the same struggle with myself: re-treat of risk straightening?

[MilwaukeeJon]

Great info. Do you start this light straightening after a certain number of minutes of tempering? 

[Joël Mercier]

Don't know about lyuv but I do it between 2 tempering cycles. 

[Jclonts82]

MJ, what is the wood used in the handle?

It has a neat almost 3d look to it.

[MilwaukeeJon]

Quartersawn white oak. I make Arts & Crafts style furniture and this is the primary wood, but also good for knife handles. 

[Stormcrow]

I use the clamp-while-tempering trick all the time.  I run one temper cycle before clamping, then clamp on the second cycle and repeat if needed.  I pull the edge past the center point.  Sometimes it needs pulled over further, sometimes it just doesn't want to work and I end up re-heat treating the blade.  With the katzbalger, it had fought me three times and I couldn't afford to dedicate more time to trying to straighten it; the gloved-hand-flex-while-still-hot-from-quenching trick worked. 

[lyuv]

I do it just like Stormcrow wrote. BUT - I"m no expert on the subject, and didn"t experiment with this method. I just follow what I heard and my common sense. It may be part superstition, part poor science and part good practice.

I have no idea how far can you bend this way before the COD (crack of death). Or even if it's significantly better than bending cold. Needs to be tested.

[Stormcrow]

LYUV - If you run the first temper cycle before doing the clamping trick, you should be able to safely pull the blade well past the center line for the subsequent temper cycles.  Of course, you can over-clamp, then have to clamp in the opposite direction to fix the new warp you put in the blade trying to straighten the original one.