Question re: m390 hira zukuri

[Rsq]

I'm working on an m390 hira zukuri style tanto. As it stands, the blade is 8.5 inches and the tang is 3.5, the stock was .2 inches, and it's still very close at the spine before the back bevel. It has slight niku, so it's not quite exactly a hira zukuri, but it's close. M390 is not typically used for fixed blades, so i'm given to think that this is because of toughness issues. I'm getting ready to refine the blade to it's final form before ht (perfect the bevels and polish it), so before I do, I'm wondering this:

1. What would be the minimum stable angle for the bevel behind the edge? How does this compare to what would be a typical angle for a traditional hira zukuri from, let's say, the kamakura period?

2. For an 8.5 inch blade on a 12x1.75x.2 inch stock, what would be appropriate instructions for peters ht (i'm obviously an amateur, and don't have the resources to even attempt an ht on my own)? I want a balanced heavy duty knife. Obviously I want the wear resistance and stainlessness, hence m390, but for a larger fixed blade, I'm wondering if the 62 rc I'd like wouldn't be sacrificing too much toughness. Given that it's a fairly thick and slightly convex blade, though, where should I have them aim? This will never be used for batonning or anything like that (barring a zombie apocalypse, it will probably never be used at all), but I'd like it to be capable.

For reference, here is the knife a few stages ago, i have significantly refined the niku since this picture, but the shape that you see hasnt changed. The knife in question is the one on the bottom

If you're curious, the smaller kwaiken is k390 and the bigger utility knife is also m390.

If you can answer any of my questions, I'd be very grateful. I'm going to post the question about how it compares to a kamakura hira zukuri tanto elsewhere as well

 

[Rsq]

Better picture

 

[Frank Niro]

Your blades look super . I don't think your information on the M390 is complete. You can grind it thin or thick and still take it to say 64 Rc and the edge will still have flexibility . This is what it's made for. Hope this helps. Frank

 

[Huntsman Knife Co. LLC.]

Hey,

I have a good bit of experience with M390. Its really, really tough even at 62. You can take it to 64. I baton wood, split pelvic bones on deer and lots of other hard activities with my personal knife in M390 and it holds up like a champ. My personal knife is at 62 and is .13 thick behind the edge with about 15 degrees per side.

As for edge thickness I'd bring it down to about .15-.20 before sharpening and then go with an angle you feel comfortable with. 20 degrees will give you a very robust edge.

Anyways have no fear about toughness issues and experiment and find what works for you. M390 is freakishly tough for a stainless steel. at 62 Id say its as tough as something like 1095 at 59-60 in terms of edge stability. M390 and ELMAX have totally changed my ideas about the role of stainless in hard use knives and big blades.

 

[Stacy E. Apelt - Bladesmith]

You have two choices on a tanto. Use crisp bevels with a shinogi, or go hira-tsukuri. I like hira-tsukuri because the blade is easier to maintain, and is probably far more authentic. Take the blade to a nearly full flat grind, with just a tad of niku....very litle The edge area should be rather thin before the final sharp edge. I like to go to .010 or less. With your choice of steel, you will have no issues with a fairly thin edge.

BTW, you need to carry the blade grind all the way back down the nakago if you plan on sliding a habaki and/or tsuba on the blade.
Also, the yokote should be a more crisp. Blending it in makes the blade look worn out. Do this by masking the blade tip with dye-chem and carefully filing/grinding/sanding/stoning the kissaki.

 

[shqxk]

Hey,

I have a good bit of experience with M390. Its really, really tough even at 62. You can take it to 64. I baton wood, split pelvic bones on deer and lots of other hard activities with my personal knife in M390 and it holds up like a champ. My personal knife is at 62 and is .13 thick behind the edge with about 15 degrees per side.

As for edge thickness I'd bring it down to about .15-.20 before sharpening and then go with an angle you feel comfortable with. 20 degrees will give you a very robust edge.

Anyways have no fear about toughness issues and experiment and find what works for you. M390 is freakishly tough for a stainless steel. at 62 Id say its as tough as something like 1095 at 59-60 in terms of edge stability. M390 and ELMAX have totally changed my ideas about the role of stainless in hard use knives and big blades.

Opposite experienced for me, I chipped my Green Para2 badly when trying to scrape some epoxy from aluminium rod. I have done similar thing on my Digi Para2 S30V with no any problem.

M390 and 204P while hold an edge greatly at cutting something like cardboard, its not a very tough stuff IMO.

 

[Rsq]

Thanks guys,
I think i'm going to take the edge down to 30 inclusive, then convex it to 20~ish to the spine. This should be a pretty minimal niku. I realized that about the habaki, I've since fixed it. As I said, this picture isnt the most recent.

About the yokote, is that necessary for a tanto? A lot of hira zukuri tanto that I've looked at have no distinct yokote.

http://sanmei.com/Pictures/Sword/H114409_T8600_PUP1.jpg

I'm about to start the last phase before ht, refining the geometry and symmetry. I have intentionally not refined the tip much because
I know that its easy to mess up. Are the examples I'm seeing without yokote worn down and only like this because of repeated polishing? I was under the impression that some tanto were intentionally made like this. If I'm wrong, I'll definitely put in a yokote. My machines are extremely limited (8 inch grinder and harbor freight belt sander), so this last part is being done by hand with a jig. I've left everything a little meaty so that i don't ruin it, so if I'm going to put in a yokote, this would be when it would happen anyway.

I think modern steels are so tough these days that anything I could do with this would probably be fine at 62-63 hrc, so that's my plan. I'm going to have a 30* edge with no bevel, and only slight niku, then I'll ask peters to ht it to 62 + or - 1 hrc, with cryo and triple temper.

Edit:
When you guys say .15-.2 or .01, can I assume the former is mm and the latter is inches? I was thinking I'd try to leave the edge at about .5mm when i send it off

 

[Rsq]

Opposite experienced for me, I chipped my Green Para2 badly when trying to scrape some epoxy from aluminium rod. I have done similar thing on my Digi Para2 S30V with no any problem.

M390 and 204P while hold an edge greatly at cutting something like cardboard, its not a very tough stuff IMO.

Metal on metal is iffy with any steel, but the para2 is a very thin edge. Hopefully the niku insulates this somewhat from that kind of impact, and there's a lot more behind this edge than a para2. It will be more akin to the gso survive in m390 that ankerson reviewed, i suspect.

 

[shqxk]

Metal on metal is iffy with any steel, but the para2 is a very thin edge. Hopefully the niku insulates this somewhat from that kind of impact, and there's a lot more behind this edge than a para2. It will be more akin to the gso survive in m390 that ankerson reviewed, i suspect.

Im sure your knives will hold much better than that. Awesome looking blade anyway bro.

 

[Stacy E. Apelt - Bladesmith]

The yokote is nicer looking with a crisp line. It is not necessary for cutting ability, but looks better. I see the ones with just a smooth bevel to the tip and think, " That would look so much better with a yokote." It takes a bit of extra effort, but it is worth it in my opinion. When you are ready for a major togi project, try doing an osaraku tsukuri tanto. I don't know if there is any blade prettier.

The kissaki is often easiest left fat pre-HT and the yokote done in the hardened state.

 

[Rsq]

Osoraku are very interesting blades. I think that they are the only true tanto form (re: made to be a tanto, not made from a broken katana) with a yokote, though. I've been looking a lot recently, and I have studied every tanto I could find from the Kyōhō Meibutsuchō, and I didnt see a single hira zukuri with yokote. I think my next project might be an osoraku zukuri, if i don't go for a yoroi doshi (maybe itnwill be both? I need to research that) but I think I'm going to model this one after meibutsu I've seen, and leave out the yokote. If you have any examples of tantos with yokote, though, I'd be very interested to see them. I like the idea of a yokote, but I want to make this resemble a 'classic' tanto to the best of my ability (within the obvious limitations of the steel and lack of hamon, though with some creative polishing, I hope to create a visual difference at the ha)

 

[Stacy E. Apelt - Bladesmith]

If you want the smooth tip of a tanto without a yokote, then make the tip O-kissaki instead of ikubi-kissaki. A longer taper to the tip will blend better without a yokote. It can even be a continuous curve.