I've been working on a knife for a customer that's creating a rather steep learning curve. He wants a "Japanese style knife with one of those fancy tips". So I came up with a design and forged 8 inch blade from some 1/4" 1084FG. I forged in the bevels and gave the blade a slight forward taper from guard to tip. The blade turned out quite well I think.

I was surprised though! When I quenched the blade it acquired a slight downward curve..... rather than the expected upward curve. The discerning eye will see the difference between photo #1 (annealed) and #2 (hardened).

Anyway, I worked that all out and now I'm in the middle of making the habaki(albeit very non-traditional). I found a series of videos on youtube that provided some basic info and a visual on how to forge and shape this thing. I started with a 5/8" pure copper plate and after three attempts and five hours of hammering and filing.... its getting there. It still needs to be thinned out and the fit need to be fine-tuned. I also need to solder in the bottom piece for under the ricasso.

I still have a damascus guard and copper spacers to forge and shape, but I can see this thing starting to take shape.

Any and all advice would be greatly appreciated.

Thanks,

Peter

If you quenched in oil, that would explain the downward curve; oil makes the curve go the opposite way from water. Looking good so far.

If you quenched in oil, that would explain the downward curve; oil makes the curve go the opposite way from water. Looking good so far.

Steve - Thanks for the explanation. Now...... why?

Why does water effect steel differently than oil?

water pulls a blade up and oil down??? whaaaa that's seems so strange, please do explane why

That is a higher plane of metallurgical understanding than I possess; I have yet to hear a simple explanation of why it happens, just that it does happen.

Steve, ML - I recieved an explanation and an interesting link from Stacy Apelt:

"I started a long treatise, but decided to just say that the curvature is caused by the differences in volume of martensite compared to austenite and pearlite. The speed of the quench will determine which structures form when.All yaki-ire blades bend down first. The water quench is fast enough to allow the martensite expansion to reverse the curve. Oil is too slow, and the downward curve remains or is slightly restored to straight.

To get a desired curvature in an oil quench ,you forge/grind in the curve, allowing for some slight downward drop. It is still hit and miss, sometimes.

Here are some great animated graphics of the process. Each chart deals with a specific structure."

http://www.swordforum.com/forums/showthread.php?92559-Yaki-ire-quenching-animated-graphics