Japanese tools - advice please

[Sawyer]

A while ago I bought an Ice Bear Japanese V pointed marking knife: http://www.axminster.co.uk/ice-bear-jap ... prod20282/

The best marking knife I've ever had.

However, the flat side is concave, as I believe all Japanese chisels are and the concave bit is now getting very near to the cutting edge. There must be a technique for increasing the flat behind the edge, probably by hammering the bevel side or something?

I've only ever used Western tools and am not familiar with Japanese tools & techniques. Could one of you Japanese tool fans advise please?

 

[GazPal]

You'd normally occasionally flatten the concave face as you re-whet the cutting edge, but I'd leave any hammering until you're familiar with what you're doing and how best to avoid cracking the harder edge steel.

 

[woodbloke]

'Tapping out' should only be done on the softer iron section of the laminate, never on the much harder cutting steel...and you need to know what you're doing! To increase the distance from the edge to the to the 'ura' (the concave bit) just flatten the back some more using a coarser grade of abrasive stone and then polish on something finer. If in doubt have a look at Mike Huntley's JTSG at the top of this page...all sorts of useful stuff on there about these sorts of tools - Rob

 

[jimi43]

Having just tapped out the back of a blade...I agree..it is a fine art...but fairly easy to get it to work.

I believe as Rob says...it is just as easy to crack or chip the hard laminate...but so far...I have erred on the soft side and kept at it.

The difference between "tapping out" and flattening is that you get a very fine cutting edge all round...and it looks pretty.

As long as you avoid the hard part of the bevel...hold the steel against a hardwood anvil in a vise and tap the soft steel like you were driving in a brass tack..you should be ok. Always move the steel from left to right and back again keeping the hammer still rather than moving the hammer.

THIS VIDEO give you an idea of how to do a plane blade...use a much smaller hammer for a marking knife.

Jim

 

[David C]

Dear oh dear,

This is the kind of thinking that caused countless people to stop using Japanese chisels when the hollow was reached.

On a chisel, ten minutes work on the flat side, on an 800 grit stone, will "move" the hollow back by about 3 mm.

For the knife I think 5 minutes might be sufficient.

The main downward force needs to be above the tip.

The stone will wear hollow very quickly so I suggest my "edge of tool off the edge of stone stone for 50% of the strokes" technique.

The technique is described in book three or two of the dvds on blade preparation.

best wishes,
David Charlesworth

 

[MickCheese]

Dear oh dear,

This is the kind of thinking that caused countless people to stop using Japanese chisels when the hollow was reached.

On a chisel, ten minutes work on the flat side, on an 800 grit stone, will "move" the hollow back by about 3 mm.

For the knife I think 5 minutes might be sufficient.

The main downward force needs to be above the tip.

The stone will wear hollow very quickly so I suggest my "edge of tool off the edge of stone stone for 50% of the strokes" technique.

The technique is described in book three or two of the dvds on blade preparation.

best wishes,
David Charlesworth

Sorry but this has confused me.

I assume the hollow disappears as you re-grind the tool until the cutting edge is almost at the hollow and therefore in danger of not being flat.

Surely if you did as above (and I assume you mean flattening the back on a stone) you would not move the hollow back just make the blade thinner.

Have I totally missed the point?

Mick

 

[David C]

Mick,

In a word yes, though the blade does get thinner.

The flat back has a shallow hollow ground in it. As metal is removed from the flat surface, the pond gets smaller and the flat area gets larger.

I am struggling to find other analogies to make this clearer. Perhaps try it with some hard butter or ice cream?

best wishes,
David

 

[dh7892]

In the case of Japanese tools, they don't have a hollow grind; they have a forged hollow on the back.

In western tools made from a single material, this wouldn't make any difference but, because the Japanese tools have a thin layer of hard steel with a much thicker section of iron, the fact that it's forged rather than ground means that the hard steel is bent into the hollow rather than being ground into the hollow. Thus the steel must be hammered out to flat when you reach the hollow or you will risk removing the hard parts at the sides before you get the blade flat.

I think some pictures would make this all clearer but I'm not in a position to post any from work.

 

[sometimewoodworker]

Sorry but this has confused me.

I assume the hollow disappears as you re-grind the tool until the cutting edge is almost at the hollow and therefore in danger of not being flat.

Surely if you did as above (and I assume you mean flattening the back on a stone) you would not move the hollow back just make the blade thinner.

Have I totally missed the point?

Mick

Yes.

When you sharpen the blade you should work on both the front and back. This means you do not get near the hollow. As every time you sharpen you move the hollow back fractionally.

If you think of the back as having a slight bevel running from the back of the blade to the tip so the hollow gets fractionally deeper the further from the cutting edge you get.

So this means that you will have to do quite a lot of work on the back that you haven't been doing up to now. I would use a diamond plate to start with.

Sumokun on YouTube has a great couple off videos on tuning up a Japanese chisel. If you look at part 2 the method is similar.

 

[dh7892]

Sorry, but I agree with MickCheese on this.

You will not be "moving" the hollow back, you will be making the blade thinner. This will mean that you get a flat edge again but, if you keep doing this as you sharpen the blade back, you will eventually flatten away the ura.

On a narrow blade such as a chisel or a marking knife, this may mean that you just have a flat-backed laminated chisel but on a wider blade like a plane blade, I think the the depth of the ura is about the same as the thickness of the hard steel in the lamination. This means that, when the blade is worn back to the point where the "lowest" point of the ura was when it was fresh, you would have had to grind away so much of the metal to get it flat that there would be no hard steel left at the sides! This seems like a bad idea to me!

What's the point of having a blade with an ura in the back if you grind it away? Why not just buy a western chisel?

Hammering out the ura looks like a delicate task that has the potential to go wrong but it is what you're supposed to do and I think it's probably worth learning if you want to maintain your tool as it's meant to be.

 

[sometimewoodworker]

Sorry, but I agree with MickCheese on this.

You will not be "moving" the hollow back, you will be making the blade thinner. This will mean that you get a flat edge again but, if you keep doing this as you sharpen the blade back, you will eventually flatten away the ura.

You should not flatten the full length of the back. Just the first 25mm. This does efectivly move the hollow back.

 

[David C]

Of course the blade gets slightly thinner as you "move" the hollow back.

Smaller chisels and knives are not tapped out as far as I know.

Plane blades are as this preserves the shape of the wedge.

David Charlesworth

 

[dh7892]

I can see that trying to tap out a small blade would be very hard to do and not really gain you much and we agree that larger blades need to be tapped.

I can see what you're saying (sometimewoodworker) about only working on part of the blade. I guess the resulting curvature you would be introducing to the back would not be much of an issue as you would still have a flat section near the edge that would work for registration.

I guess I'm just thinking in terms of wider (plane) blades which I still think would need to be tapped out in order to avoid wearing the sides to thin.

On my japanese marking knives, the ura is reasonably large compared to, say, a chisel so I think I'd still want to tap that out a bit but I've got a good few sharpenings before that will need to happen.

 

[SteveJ]

Personally I would avoid tapping out a marking knife, they tend to be thin in section and wouldn't stand much abuse. With a balanced sharpening regime you should have no issues, the key is to remove metal from the entire back side of chisel / knife (or as much as is practical in the case of a knife) but to preferentially apply pressure to the point / tip removing most material there and as little as possible the heel. As the bevel works back with successive sharpening you're working back up towards the thick end of the wedge you've created in this process and hence should not need to worry about thinning the blade. It was my understanding that the hollow or ura is something of a happy accident - the chisel is shaped that way for the same reason that samurai swords are not straight; when quenched the two materials contract by lesser or greater degrees creating the sweep in the sword or hollow in the chisel. In the case of the chisel the edges of said hollow can then be ground flat - in evidence by the fact that most chisels appear to have more of the hard steel layer in the centre of the chisel. It wasn't forged that way, its just the outside edges have been ground off afterwards to create the flat portions of the back, only possible if the hollow was created in the forging process (though doubtless they can be and are refined afterwards).

 

[sometimewoodworker]

I can see what you're saying (sometimewoodworker) about only working on part of the blade. I guess the resulting curvature you would be introducing to the back would not be much of an issue as you would still have a flat section near the edge that would work for registration.

I guess I'm just thinking in terms of wider (plane) blades which I still think would need to be tapped out in order to avoid wearing the sides to thin.

On my japanese marking knives, the ura is reasonably large compared to, say, a chisel so I think I'd still want to tap that out a bit but I've got a good few sharpenings before that will need to happen.

Either you have misunderstood or my explanation was not clear enough. There is NO curvature introduced into the back.

When you sharpen (every time, or at least every 2 or 3 times, you sharpen) you work on the back first. This fractionally changes the angle that the back forms with the front (unsharpened part) of the chisel. The back is kept flat, you work on the front part of the chisel with pressure on the bevel and as the flat part of sides are very thin you will fractionally change the angle.

My understanding is that chisels and knives are never taped out here and are not designed for that. Unfortunately none of my students are into woodworking so I can't get the information from them.

From what you have said you have only worked on the bevel side of your knife. If so then the next few times you sharpen you will need to work on the back.

It was my understanding that the hollow or ura is something of a happy accident - the chisel is shaped that way for the same reason that samurai swords are not straight; when quenched the two materials contract by lesser or greater degrees creating the sweep in the sword or hollow in the chisel. In the case of the chisel the edges of said hollow can then be ground flat - in evidence by the fact that most chisels appear to have more of the hard steel layer in the centre of the chisel. It wasn't forged that way, its just the outside edges have been ground off afterwards to create the flat portions of the back, only possible if the hollow was created in the forging process (though doubtless they can be and are refined afterwards).

I doubt that there was any kind of accident involved happy or otherwise. Unless you think that scientific research qualifies as :shock: accidents. :shock:

There was (and is) a deep understanding of metallurgy involved. Far more than in almost other steel making. You are absolutely correct that the curve in the Katana and other swords is a function of the final heating and quenching of the sword blank. Swords are forged and formed straight and only after many weeks of work is the final tempering done and the maker finds out if he has a sword or useless piece of very expensive steel.

 

[Benchwayze]

First off, I have no experience of Japanese chisels. I can see why the hollow is there, be it ground or forged. (The latter I think). It must be easier to flatten the face, but as the hollow creeps back, I can't see how the blade doesn't get thinner. There must come a time when the chisel is worn out, due to losing the harder laminate; worn away from flattening. Just as the chisel will get shorter due to beveling. (Single bevel I believe.)

I was interested in David's mention of hanging most of the chisel 'off the stone'. This is what I do with plane irons, to ensure a flat face right up to the edge, for the chip-breaker to rest on; as opposed to using the 'ruler-trick'.

Overall though, the problems with the hollow and the laminated blades, are the reasons I stick with Western chisels; and old ones at that. (I don't have any laminated ones that I know of.)

I dare say Japanese chisels, especially these days, are better made than ours; but our forefathers seemed to manage quite well, when our steel was also good stuff. Also I believe that in the main, Japanese workers worked with far softer timbers than we do over here. I might be up the proverbial 'gum-tree' here, as I don't know for sure.

Again, having never used Japanese chisels, I might be denying myself a pleasurable work experience; but they do say ignorance is bliss!

 

[GazPal]

The hollow is forged in (In the case of handmade Japanese blades) as a traditional means of spreading precious tamahagane as it's forged into the iron back/main body of the tool or blade. Japanese knives are traditionally sharpened/polished on one face only, with this being the flat of the blade.

 

[Harbo]

There's an article in the latest BWW where David Savage explains why he reckons old chisels are better.
Modern steels, are chemically more consistent but are cold rolled whereas the older steels were hot forged. This applies to both Western and Japanese types ( probably more so for Japanese as some are still made this way?).
The hot forging lines up the carbon atoms more closely and gives a steel that gives a sharper edge.
Modern steels give better edge retention but the older steels give a finer and sharper edge.
The above is a very short summary - he also talks about handles and that on older chisels they were made to suit the blade and better balanced?

Rod

 

[woodbloke]

There was (and is) a deep understanding of metallurgy involved. Far more than in almost other steel making. You are absolutely correct that the curve in the Katana and other swords is a function of the final heating and quenching of the sword blank. Swords are forged and formed straight and only after many weeks of work is the final tempering done and the maker finds out if he has a sword or useless piece of very expensive steel.

Having just returned from Japan and having spent a day with a professional swordsmith (where the final sword will set you back a cool £30K) it takes two weeks to forge the blade and the essential shape is produced in the forge, not by the last final heating. The particular maker I was with is licensed by the Japanese gov to make 24 blades per year, which is roughly two per month. In fact the rough edge is ground on a Makita belt sander :shock: The 'hamon' is made by a applying a slurry of ore and charcoal to the blade after it's finished to the correct shape...there may be some alteration in it after it comes out of the heat, but it's not much. PBucket doesn't seem to be working at the moment, but you can read about making a sword on the Blog

 

[MickCheese]

Mick,

In a word yes, though the blade does get thinner.

The flat back has a shallow hollow ground in it. As metal is removed from the flat surface, the pond gets smaller and the flat area gets larger.

I am struggling to find other analogies to make this clearer. Perhaps try it with some hard butter or ice cream?

best wishes,
David

Thanks

That makes some sense now. Just couldn't get my head around it!

Mick