Not as easy as it looks!!

P. McKinley

P. McKinley

Joined
Jan 27, 2008
Messages
2,010
And it doesn't look all that easy!!

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 of Aldo's 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. :ssmile: 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.





 
No real advice except that I like photo #2 better than photo #1... so good job with the reverse bend in the quench. I am sure that is what you were intending.
 
I believe the downward bend was fortuitous. Nice blade.

Fred
 
Weird it would bend that way. How did you apply the clay?(if at all) What did you quench into and is your quench tank vertical, ie. did you quench tip first or edge in first, ie. horizontal?

Nice looking design.
 
agreed. i like #2 better. the edge on number 2 is clearly straighter, but i dont see any difference in the spine.
 
Let me guess, you quenched in oil? It is common to have a downward curve when quenching in oil. You get an upward curve when quenched in water. The long profiled blades show this much more dramatically. If you want a more straight blade you need to allow for the curve. It really becomes apparent when you do 2 or 3 quenches trying to get the Hamon right. Had to reforge a blade to remove the curve on one knife.
 
Thanks guys.

Chuck -
It is common to have a downward curve when quenching in oil. You get an upward curve when quenched in water.
Click to expand...
..... REALLY!! WOW!! I quench all of my blades in oil. Never tried a water quench. I can't say I've ever noticed any noticeable curve, up or down, in any previous blade. I'll have to start paying attention!

Stuart - No clay, just a clean blade at 400 grit, quenched tip first into a vertical tank (old Coke cylinder) of 120 degree canola oil.
 
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
 
Stacey - It never ceases to amaze me - the volume of detailed info you have to offer..... and your propensity for sharing it so willingly! Thank you!!

This is the first "Japanese-style" blade I've attempted. I tried to keep some of the elements found in the traditional blades including the basic profile and shape, a distinct yokate, habaki, seppa(s), fuchi, and tsuba.... but, all quite non-traditional and stylized. I like doing small detail work so I'm enjoying this project immensely.

Thanks for the help
 
Yokote - The line between the point where the edge ha meets the kissaki ha, and the mitsukado.
 
Interesting. I didn't know about the difference between the water and oil quench. Would that still apply with using Parks50 which is undoubtedly faster than Canola but slower than water?

So would this occur because there is more steel volume in the spine and thus more expansion? Also could the fact that water quenches are interrupted cause a slow down in the cooling of the spine and thus less expansion?
 
The down curve is caused by the austenite cooling and thus contracting a bit, plus the pearlite expanding. The upward curve is caused by the expansion is in the martensitic edge as the super-cooled austenite converts to a larger spaced martensite.. The interrupted quench is to prevent the edge from cooling too fast and becoming too brittle martensite before the blade is ready for that. It is also a slight auto-tempering process. The violent force applied to the blade during the martensitic conversion is what breaks many blades with the dreaded "PING".

I use parks 50 and forge in the sori on most blades. If you are going for a hamon, and want all the ashi and clouds, then water is your friend.....but it also is your enemy.

OK, I'll give you the longer explanation.
There are three structures involved in a blade of differential hardness.
Austenite is a compact and rubbery structure.
Pearlite is a larger structure that is soft.
Martensite is a much larger structure and is hard....and brittle when just formed.

Steel changes into austenite as it crosses Ac1 and when it reaches Ac3 it is fully austenitic. As it cools down past Ar1, it will convert to pearlite if cooled slow enough to enter the pearlite range....or stay as austenite if it misses the pearlite nose. As the super-cooled austenite continues down until it hits the Ms, the austenite suddenly converts into martensite.

Now, the austenitic blade with the clay coated back is fully heated to Ac3. It is all austenite, even under the clay. We quench it in a media that will drop the edge to below the pearlite nose around 1000F, and thus keep the edge austenite at this point. At the same time, the coated spine cools a bit slower, and goes into pearlite, which expands a bit. The larger pearlite pushes the soft austenite edge , causing a downward curve. All is happy at this point with a soft pearlite spine and a rubbery austenite edge. Then the martensitic conversion point is hit by the edge, and the edge suddenly gets a lot larger ( relatively), causing a quick push on the soft pearlite ,resulting is a sudden upward curve. This is happening at the same time as the edge becomes hard and brittle. If it all happens at exactly the right time and speed, you get a nice sori and a good hamon. If it happens a few milliseconds out of sync, you get a nice sori and a broken or cracked blade.

All that is fine for a fast water quench, but with oil, which is slower, the martensitic edge is auto tempered and the whole blade just stretches out a bit when the conversion happens.The oil also is slower, and the pearlite gets a bit cooler, and thus stiffer, when the conversion happens. This only slightly reverses the downward curve. Most times you never know that it curved down and then back up to straight or near straight. It is only really an observable feature on longer and thinner blades. I usually figure twice the up curve for every amount down in a water quench, and about 80% up from the down on an oil quench.
 
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even the parks 50 will make the tip drop (tuna sword taught me that a few months ago) i ended up water quench for 3 sec then into parks to finish (came out 99% straight jsut the way i wanted it )
 
Here's a few progress photos of this knife.

The wife stole the camera for a couple of days so I was unable to get in-progress shots of the random pattern damascus guard.

I'll post more shots later.

I spent a day hammering a nice tight fit for the habaki. This piece, as with all the copper, began life as a 1/4" electrical bus bar. :


A wedge of copper was soldered in place to connect the habaki at the bottom. Getting the fit correct with that small wedge was a PITA!! I think it came out just fine though. This piece is now ready for final shaping and sanding.


The seppa was hammered out to approx 1/16" thick:


A bit of hand sanding:


Check the fit:


Checking the fit of the front ferrule on the handle. This piece was drilled out and filed to shape, and will later be soldered to the seppa and then fine tuned for fit and shape:


The unfinished blade and handle along with habaki, seppa, tsuba, and the two pieces of the fuchi(which I will solder together later).






 
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Nice wip. I see it takes a lot filing to make all the handle pieces.

I'll drop in again soon, Fred
 
I just love traditional Japanese blades. Maybe by next year ill have the huevos to try one! After I try a few other things first.

Looking good so far, ill be checking back often.


-Xander
 
Bigblue17 said:
Xander -

Me too. But, this one's about as far from traditional as they get!!
Click to expand...

Yeah, I realise the blade shape is off, but your methods and construction really make it part of that catagory. At least to me, which I know very little of traditional japanese edged tools/weapons, but I sure do know what I like!

Great work!


-Xander
 
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