Thread: should new chisel edges be square?

Thanks, Steve --

Do you use a gennou (or genno, depending on where you're from), or a narrow-tipped hammer? I generally like the control I have with a small tap hammer (really narrow tip -- but not so narrow it punctures the metal). But would welcome knowing what you use.

Ceramic blade's a great suggestion, as is the hacksaw/cheap blade method. Will try to find someone with a grown-up size table saw (I'm not big on machines, and only have a puny 4" (yeah, that's what I said -- you got a problem with that?) table saw. All I really need. Well, there's also an adult-size chopsaw, but I wouldn't trust it not to blast the stone into powder. Otherwise, it's the hacksaw for me!

Thanks, Steve. You are, as has always been the case, a peach.

Becky

You know Becky hammer size and so on is personal.

I would recommend though getting one that is big enough for the job. A little one you have to really swing to do anything so you have less control than a bigger hammer. Of course a really big one will be too heavy to use the way you want to.

Just a thought but a Ball Pene hammer should be just the shot. Using the round end of the hammer.

Studley

Hey, Studley,

Sorry to get so personal about size...

Thanks for the information. The few times I've set myself to uradashi (have done more on nomi than kanna, as I use them more), I've worked with the smallish hammer I described -- actually, mis-described (un-described?!), since it's got a horizontally flat tip, about 1/2 inch (1.27 cm, by my desktop converter -- can that be right?) and is nicely balanced. Will certainly try with a larger head.

Never have chipped the top of the blade -- and am horrified to hear I could! What I did with caution but no terror will now become a Hitchcockian nightmare... Ah, never mind. I'll get over it. The ball peen's an interesting idea, though I'd worry about seeing as well, since the ball will, of necessity, occasionally obscure my view of the blade. I'll give it a try on a really shot old kanna I've got. No great loss if I screw up, and I may find it works great.

I have a small flat metal anvil that sits on my larger one (which is fairly small, itself -- a bit of old rail). Never even thought to use wood. Are there advantages to wood, do you think?

Since my skills are still being developed, I'm very cautious: takes a long time. I've seen footage of Japanese carpenters doing it, and they work with lightning speed -- of course, they've been doing it for far longer than I. Perhaps a medium gennou will help.

Thanks much, Studley.
Becky

*L* nothing personal. I use a bit of hardwood because I don't have an anvil. An anvil would be great if I had one.

Studley

Becky, Studley,

I use a fairly small (300 g) hammer with a cross peen on one end (22 mm or 7/8". I won't call it a genno because its Chinese - Flying Swallow Brand). I have a steel anvil (also a piece of old railway track - picked it up myself some years ago when they were repairing a line nearby), but I prefer wood as it's feedback is more to my liking. I've only corrected kanna that have been sharpened up to the hollow through use, so nothing radical required in terms of correction. Hence, only a little bit of tapping needed and my hammer is perfect (I hit with the cross peen at an angle so only a corner hits and makes a small indentation - very easy to be accurate). As Studley described, start at the top of the bevel (as much to ensure first taps are not going to go errant towards the edge steel) and work across the bevel with more hits in the middle. I never go past midway on the bevel (very little steel in terms of depth there and as you near the edge so you risk making the hard steel move too much and crack).

Becky, if you've been able to do uradashi on nomi successfully, I think you won't have trouble with kanna.

Steve

Perhaps I'll start feeling a little more confident now. Interesting what you say about the feedback from wood, Steve. I'll have to try that. Can't say I feel, er, uninformed by the anvil -- to me it's the sound of the hammer strike that lets me know how I'm doing (but then, I gather a lot of information by sound) -- but the wood might give it quite a different feel. Next time, I'll hit the scrap pile and find a good bit to use.

Thanks, fellas.

For tapping out, I've used a ball peen hammer and the pointy end of a Japanese hammer, and did my tapping on the end grain of a piece of scrap white oak. I haven't found much difference between the two hammers, but then again I'm not so sure about my overall technique. The times I've tried to tap out a plane blade or wide chisel, I tended to go back and forth between tapping and flattening the back, and I was never sure as to how much the tapping contributed to the process.

To go back to hollow grinds, I've used a Tormek when reestablishing the bevel angle on a plane blade or chisel, and you do get a hollow from that. But because the wheel on the Tormek has such a large diameter (mine's currently at 240 mm), the hollow is really shallow, and goes away fairly quickly as you work on the bevel side.

I wouldn't use a dry wheel grinder on a Japanese tool. My understanding is that since they use high carbon steel, the range of temperatures for tempering is fairly narrow, which is one of the reasons that it takes a lot of skill to make these tools. Likewise, there's not much of a safety margin if you overheat the tool while dry grinding it. But maybe I'm just paranoid.

Gunna Check Machinery's Handbook tomorrow on that one.

Basically Steel is Iron with Carbon in it. I don't think the carbon in the Japanese steels, that is hand smithed tool steels, is out of the ordinary.

I can say though that one of the major reason for the grain and other features of japanese tools is due to the smithing/forging process.

Studley

if you want to get an idea of steel check machinery's handbook. There are as many flavours of steel as you care to name.

When you check, see if they say what the carbon content of the steel is. The term "high carbon steel" seems to refer to any steel with a carbon content of 0.5% and up, but the carbon content of the steels used in Japanese tools is higher - 1% minimum, more often in the 1.2-1.4% range, and that seems to be the difference.

I do agree that the hand forging process is a big component in how these tools behave.

Its not only the carbon content, but the size (very small - microscopic level) of the carbide particles and their distribution within the steel matrix (very evenly distributed as opposed to clumped together in clusters) which makes Japanese steels so fine and capable of taking an extremely sharp edge. Most of the Japanese tool edge steels come from companies like Hitachi and other than the laminating/hardening/tempering, are relatively unchanged by the blacksmith (certainly an incredible amount of skill and knowledge required to put it all into a hand-forged tool).

Steve

I don't have a Tormek/equivalent; the 240 grit stone has always done the job unless really badly chipped in which case I've carefully used the cheapo 6" grinder with a white stone. I think when I get a minute to myself (in middle of bathroom refit) I'll try the 1200 grit and then a 240 if things are too slow to straighten the edge up. I've heard Becky's idea before and have also seen horizontal waterstones before but have always wondered about the ease of keeping the surface level as my 240 stone has needed dressing a couple of times.

On further examination the hollows on the chisels I've just bought are really close to the edge so the backs should be pretty easy to lap.

Thanks again all am amazed at the responses really helpful!

On a different note anyone got any pictures that explain the 'laminated' structure of Japanese chisels?

thanks

Paul

Paul,

Have you looked at the thread "How to Sharpen a Plane Blade Part 1"? There are drawings of a kanna (but the same is for nomi - just imagine a skinny tang attached. Although with nomi, the hard steel wraps up the side whereas with kanna, it is just laid flat accross) with colours to denote hard and soft steel.

When you look at your own nomi, you can see the difference in the two steels by the colour (generally, hard is shiny whitish and soft is dull grayish). Look closely and you can see where the two steels meet up the sides and at the tang.

As for tools that have a laminated structure within the soft steel, this can be seen best at the bevel although sometimes the effect is carried out to all the surfaces of the tool (except the hard steel) for cosmetic appeal. Because of the forging of this type of steel, layers are created (due to mixing of different steels or the manipulation/modification of the soft steel - not for cosmetic reasons) before the hard steel is welded to it, and these layers become visible as a colour contrast (shades of gray - sometimes obvious, sometimes subtle) when the bevel is sharpened with natural stone (it may be visible with man-made stone, but is most visible with natural stone - "Play Kasumi For Me" ).

If you look at pictures of Japanese swords, for example:
http://www.aoi-art.com/sword/katana/08367.html,
you can see one example of the "grain" in the steel and the change in colour between hard and soft steel (although here, the process is different than in tool construction. You can study the making of traditional swords if you wish to know more about them - a whole new world of study if you get into it).

Perhaps a pic is worth 1000 words: not the best example and my polish is lacking, but you can see some layers within the bevel. Often, the soft steel is as prized as the edge steel.

Hope this helps,

Steve

Originally Posted by wilburpan

When you check, see if they say what the carbon content of the steel is. The term "high carbon steel" seems to refer to any steel with a carbon content of 0.5% and up, but the carbon content of the steels used in Japanese tools is higher - 1% minimum, more often in the 1.2-1.4% range, and that seems to be the difference.

I do agree that the hand forging process is a big component in how these tools behave.

This is one where things can be confused. Machinery's Handbook says, "Steel is the generic term for a large family of iron carbon alloys, which are malleable within some temperature range".

Later it says:

Carbon Steel: A steel qualifies as a carbon steel when its manganese content is limited to 1.65% (max), silicone to 0.60% (max), and copper to 0.60% (max).

Anyway looking a bit further if you look at what a basic mild steel is compared to better stuff. I am pulling out a few grades here because I am familiar with them. 1012 or basic mild, 1040 nice steel you can machine well and heat treat also often used for hubs and bearing shafts, 4140 steel can be hardened to about Rc60 though it is typically left around Rc35-40. It is popular for Hydraulic Shafts.

1012 has 0.1 to 0.15% Carbon
1040 has 0.37 to 0.44% Carbon
4140 has 0.38 to 0.43% Carbon

Checking further Machinery's (aka The Bible) says that, "The Maximum attainable hardness of any steel depends solely on carbon content". When I was an apprentice they used to say you have to have carbon to make it hard, means the same thing.

When you get to tool steels one you might all know is A2. Plane blades are often made of this. It is called A2 because it is the second one in the Air Cooling series. Used for cold work which lets face it is what planing is.

Anyway to the point A2 has 1% Carbon 1% Molybdenum and 5% Chrome. You do see it up around Rc60 and as high as Rc62.

So A2 hardness is very similar to that of Japanese blades but they are quiet different. Either way I think it is safe to assume the Japanese blades have a similar carbon content to A2.

The crucial thing I think in Japanese blades is the formation of Austenite under the forging process. It is important to remember that the hard steel the Japanese Smiths use is very brittle. To overcome this they laminate it to a piece of soft steel. I don't know enough about this but I think they use a very low carbon steel such as 1012 or even iron so that the whole blade can be heat treated in it's laminated state without hardening the back of the blade. Western steels they tried to produce steel that was able to do everything by itself. Of if you like they got the qualities they needed by adding things to it such as Chrome and by heat treatment also. The Japanese answered the same question by joining two different bits of steel.

Studley

Just an amusing interjection, since Studley's brought up molybdenum:

During WWII, the cork that comprised the center of baseballs was needed for the war effort. So they decided to replace it with molybdenum. The results were disastrous: hard-hit balls fell like dead birds a couple of feet from home plate. If Babe Ruth had been playing (he used a 52-ounce bat, compared with the +/- 30-32 ounce bats used today), maybe, just maybe, he could've hit one just over the pitcher's head.

Totally useless information, brought to you for no apparent reason.

Cheers,
Becky