Stock removal curved blade?

oic0

oic0

Joined
Jun 16, 2012
Messages
368
I'm sure there are multiple ways to tackle this problem, I'm just wondering how you guys suggest adding the curve.

I had fun making a tanto and the end result came out much nicer than I expected. I enjoyed both that blade style and the handle. A moment of boredom had me ordering a 36"x1.5"x0.3" piece of L6 to ruin. Not wide enough to grind a curve in and not the kind of steel to use clay and water (I'm not that brave anyway). I'm not going for traditional, just functional, but some degree of curve (sori) is darn near required to visually identify as a "katana". Any advice is greatly appreciated.
 
I would say that your only option may be to forge the curve in before grinding. That's also going to be a mighty thick katana.
 
I have not done this with high carbon steels so it may or may not work. I have a $99 tubing roll bender that I bought from Harbor Freight a few years ago. I have made several modifications to it including purchasing several die sets from SWAG Offroad. One of the dies he sells is for turning rings with barstock on edge. The radius is adjustable from no bend to about 10". Could be worth it if you were going to use the roller with any frequency.

Most established steel fabrication shops will have a powered roll bender that does the same thing. Maybe you could find someone local to put an arc in your blank. The downside is that there will be a section at each end that cannot be bent. Depending on the machine, that length could be 4-8 inches.

Bob
 
I never have figured out how they measure stock thickness, I probably should. The stock I got is rated at 0.275 / 0.3. I assumed that meant it was somewhere in that range? 0.25 would be ideal but the next step down is 0.207-0.227. Can always remove material but not put it back so I guess ill taper it. Also its 1.25 wide not 1.5 like I said above.
Would bending it cold be a horrible idea? I was thinking maybe clamp lay it on an I beam with two bolts through it to brace the ends and and push in the middle? Or maybe slowly work it cold? Would normalization fix those stresses?
 
Just heat it up and forge in the sori. Even if you are going to do complete stock removal, this is where you should start. If you don't have a forge, a visit to someone who does is in store.

If planning on doing stock removal, you have two forging options. One is to heat the bar up and forge in a basic sori by hammering from the edge over the bick/horn. This will leave the billet the same thickness as it was before. The second is to start forging in a very slight bevel from the flat sides of the bar. This will automatically make the blade curve up.

I don't see any problem with the current thickness if making a classic shinogi-tsukuri katana.
 
I don't care for hitting anything with a hammer if I can avoid it, it's too easy for me to hit it wrong.


How about putting it flat in the vise, gripping it from one end.

Then grab the end and walk towards the wall / bench / vise.

Maybe you need some leverage, add a long long pipe or something.



You may have to flatten it again as it can twist



Or if you have a nice bench vise, try the three point bend technique, only in the direction you want.
 
Any attempts to cold bend a 36" bar of steel on the thin dimension will have serious problems. Twist is almost a guarantee. Additionally, the stresses introduced may come back to haunt you in HT. It is far better to heat it to around 1600F and bend it. Then flatten if needed. If you have the equipment, normalize after the sori is added. If not, make sure the HTer does a full normalization cycle as part of his HT program.

The easiest solution is to but steel in the right size. If you had ordered 2" steel you would have all the room you need to get the desired sori. Check with your supplier about sending the bar back and getting a wider bar....or just keep this one for making a matching wakizashi and tanto and order another bar for the katana.
 
I wouldn't suggest cold bending flatstock... especially L6 if you aren't fully spheroidized. Heating L6 up to forging temperature poses a problem as well, if you aren't set up to spheroidize after. I suspect that you got the L6 from Aldo and if I'm right it is Carpenter(RDS)... In my experience, that stuff hardens if you fart on it in a snowstorm(I've heard the Crucible stuff is even worse). Savor that image... ha!:p
 
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Buy wide sheets and cut to shape. No internal stress for the metal, and a lot less stress for the maker.

P.S. If you must fart, doing so in a snow storm is preferable.
 
I'll see if I can heat it up with the torch I use to treat simple steel and tap along the edge to add a minute amount of bevel. I don't need a lot of sori, I would be happy with half an inch give or take.


*edit*
Nevermind, Rick is right. The stuff air hardens and I do not have the ability to anneal it again. Well dang, dunno what Ill do then. A straight katana would look sort of odd. Think those are called ninjato or some such and basically made up for Hollywood and mall ninjas. I'll figure something out though or just make something else with it. I've got all ceramic belts, I may try doing the bulk of the grinding, then heating and bending. I was going to do convex anyhow so draw filing was out from the get go.
 
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A 1.5" X 36" bar will make a shoto-katana with a mihaba of 1.2" and a .3" sori. The nagasa will be about 28" and the nakago about 8". Or, shorten the nagasa to 24" and the .3 sori should be about right.
 
Beware the "tip-dip" reverse sori! leave some stock on the edge towards the tip and quench spine first.
 
I was bad and beat it in cold. I was surprised with how little effort it took just tap tapping with a 4lb hammer along the edge on both sides then more to get it flat again. Will normalization take care of the stresses I introduced? On that note, my old man had a really old anvil buried under a bush he dug up and let me have. The back tail part with the hole in it was broken off about 40 years ago by somone using a 25lb hammer.
2dgt00o.jpg
 
oic0 said:
Will normalization take care of the stresses I introduced?
Click to expand...
If you only managed to induce dislocations, normalizing from 1600F with a couple more cycles at reduced increments(1500F and 1450) should take care of it. If you created fractures... there is no hope for you... Ha!
 
I have come across a bigger problem now. I am not strong enough to do more than a dozen passes or so before my left hand starts to give out and I risk screwing up my sofar symmetrical grind (one hand holds handle, other stabilizes tip and applies pressure). Its going to take me a year to finish this thing lol.
 
oic0 said:
I have come across a bigger problem now. I am not strong enough to do more than a dozen passes or so before my left hand starts to give out and I risk screwing up my sofar symmetrical grind (one hand holds handle, other stabilizes tip and applies pressure). Its going to take me a year to finish this thing lol.
Click to expand...
Have you tried this stock removal method/trick shown by Philip Patton? It may allow you to remove a good majority of the stock before you have to set the primary bevel grind, making it easier on your arm muscles. Or maybe it's time to start a push-up regimen lol?
(Image used belongs to forum member Philip Patton)
 
91wm6 said:
Have you tried this stock removal method/trick shown by Philip Patton? It may allow you to remove a good majority of the stock before you have to set the primary bevel grind, making it easier on your arm muscles. Or maybe it's time to start a push-up regimen lol?
(Image used belongs to forum member Philip Patton)
[
Click to expand...

What is the method?
One of the main things slowing me down is it is convex and I can only apply so much pressure to the slack belt before im just operating the spring loaded tension wheel and slackening the belt, thus making my grind inconsistent. It probably would have been faster to start flat grind and then turn it into a convex but im roughly halfway there now (I attached a big weigh to the end of the handle to make it more balanced and much easier to hold).
 
oic0 said:
What is the method?
One of the main things slowing me down is it is convex and I can only apply so much pressure to the slack belt before im just operating the spring loaded tension wheel and slackening the belt, thus making my grind inconsistent. It probably would have been faster to start flat grind and then turn it into a convex but im roughly halfway there now (I attached a big weigh to the end of the handle to make it more balanced and much easier to hold).
Click to expand...
He grinds a 45 degree angle pre bevel near the edge using a worn belt, so when he grinds the main bevel with a new belt, it cuts better and there is less overall material to remove. It appears to work very well on long, wide, curved blades like the one pictured. It's similar in theory to forming a convex grind with a file, using multiple passes. If you used this technique, your passes on the grinder should theoretically go much faster, which translates into less work on your arm muscles that are being forced to maintain such a wide/awkward hold on the blade. Just a thought, since you are experiencing muscle failure in your left arm/hand. Then again, a simpler option may be to wear a wrist brace/wrap to assist the muscles with supporting the weight of the blade.
 
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