Japanese tools - advice please

[sometimewoodworker]

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.

As I understand it is the quenching, or tempering, that forms most of the final shape and it is quit a pronounced change. The reason being that the steels will contract at different rates.

From your own link

At this time he also adds a small amount of curvature to the blade, keeping in mind that this curvature will increase during heat treatment and subsequent tempering.

 

[dh7892]

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

I'm sorry but if you do as you say, you will not be keeping completely flat back.

If, as SteveJ says, you lap the whole back but put pressure on the tip more, I can see how you would keep a flat back but the front and back faces would no longer be parallel. But, if you just lap the first 25mm then how can you not be introducing a change of angle along the length?

I agree that it might be small and that it might not matter (hence my comment before) but it's definitely there.

As to you other point, yes, I do realise that, to make a blade truly sharp, you must work both sides. That is, after all, the whole point of having the hollow; so you can do this with less effort.

In addition, for a knife, since it's used more as a point tool than a blade (at least, that's how I use mine) you also need to polish the side to keep the point sharp.

Just to re-iterate: I'm happy to concede that it's not a great idea to try to tap out smaller blades as I can see that they would be more trouble than it's worth.

When I get a chance, I'll try to take some measurements of the thickness of the steel laminate vs the hollow's depth to see how much of the steel would be left at the sides once the edge has been sharpened back to the lowest point in the hollow.

 

[woodbloke]

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.

As I understand it is the quenching, or tempering, that forms most of the final shape and it is quit a pronounced change. The reason being that the steels will contract at different rates.

From your own link

At this time he also adds a small amount of curvature to the blade, keeping in mind that this curvature will increase during heat treatment and subsequent tempering.

Yes, that's true, it does add a little, but only a very small amount, to the shape of the finished blade. The popular myth and misconception is that the curve is produced only by the application of the hamon slurry and subsequent final heat treatment in the forge...this is not the case. The shape of the blade is determined by the swordsmith during the forging process, not at the end.
There are two other points to consider as well, firstly that from my experience of the country, it's not within their psyche to leave such an important thing as the final shape to mere chance alone, hoping that a straight blade will turn into a curved one at the final heat treatment...if it's meant to be curved, it will have been deliberately made curved. Secondly, the swordsmith also produces straight bladed weapons with no curve to the blade (one can be seen in the Blog being initially honed by Fujiyasu-san's disciple)...these blades are again deliberately made straight with no curve
Yes, the final heat treatment will affect the curvature, but to a very, very small degree - Rob

 

[sometimewoodworker]

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

I'm sorry but if you do as you say, you will not be keeping completely flat back.

If, as SteveJ says, you lap the whole back but put pressure on the tip more, I can see how you would keep a flat back but the front and back faces would no longer be parallel. But, if you just lap the first 25mm then how can you not be introducing a change of angle along the length?

As I said

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.

I agree that it might be small and that it might not matter (hence my comment before) but it's definitely there.

that is true as I said

As to you other point, yes, I do realise that, to make a blade truly sharp, you must work both sides. That is, after all, the whole point of having the hollow; so you can do this with less effort.

Spot on. The perfect reason.

When I get a chance, I'll try to take some measurements of the thickness of the steel laminate vs the hollow's depth to see how much of the steel would be left at the sides once the edge has been sharpened back to the lowest point in the hollow.

Do you mean when the blade is almost used up? Or when you get to the hollow when the blade is new?

Here is a useful link The Takenaka Carpentry Tools Museum

 

[sometimewoodworker]

Yes, that's true, it does add a little, but only a very small amount, to the shape of the finished blade. The popular myth and misconception is that the curve is produced only by the application of the hamon slurry and subsequent final heat treatment in the forge...this is not the case. The shape of the blade is determined by the swordsmith during the forging process, not at the end.
There are two other points to consider as well, firstly that from my experience of the country, it's not within their psyche to leave such an important thing as the final shape to mere chance alone, hoping that a straight blade will turn into a curved one at the final heat treatment...if it's meant to be curved, it will have been deliberately made curved. Secondly, the swordsmith also produces straight bladed weapons with no curve to the blade (one can be seen in the Blog being initially honed by Fujiyasu-san's disciple)...these blades are again deliberately made straight with no curve
Yes, the final heat treatment will affect the curvature, but to a very, very small degree - Rob

It looks as if you need to correct Wikipedia among others
:?

The gentle curvature of a katana is attained by a process of quenching; the sword maker coats the blade with several layers of a wet clay slurry which is a special concoction unique to each sword maker, but generally composed of clay, water, and sometimes ash, grinding stone powder and/or rust. The edge of the blade is coated with a thinner layer than the sides and spine of the sword, then it is heated and then quenched in water (some sword makers use oil to quench the blade). The clay slurry provides heat insulation so that only the blade's edge will be hardened with quenching and it also causes the blade to curve due to reduced lattice strain along the spine.

 

[woodbloke]

Yes, that's true, it does add a little, but only a very small amount, to the shape of the finished blade. The popular myth and misconception is that the curve is produced only by the application of the hamon slurry and subsequent final heat treatment in the forge...this is not the case. The shape of the blade is determined by the swordsmith during the forging process, not at the end.
There are two other points to consider as well, firstly that from my experience of the country, it's not within their psyche to leave such an important thing as the final shape to mere chance alone, hoping that a straight blade will turn into a curved one at the final heat treatment...if it's meant to be curved, it will have been deliberately made curved. Secondly, the swordsmith also produces straight bladed weapons with no curve to the blade (one can be seen in the Blog being initially honed by Fujiyasu-san's disciple)...these blades are again deliberately made straight with no curve
Yes, the final heat treatment will affect the curvature, but to a very, very small degree - Rob

It looks as if you need to correct Wikipedia among others
:?

The gentle curvature of a katana is attained by a process of quenching; the sword maker coats the blade with several layers of a wet clay slurry which is a special concoction unique to each sword maker, but generally composed of clay, water, and sometimes ash, grinding stone powder and/or rust. The edge of the blade is coated with a thinner layer than the sides and spine of the sword, then it is heated and then quenched in water (some sword makers use oil to quench the blade). The clay slurry provides heat insulation so that only the blade's edge will be hardened with quenching and it also causes the blade to curve due to reduced lattice strain along the spine.

Well, that may be the case, but I was there and asked the question(s). If you look on that Blog entry, there's a pic of me holding a rough, unfinished, but curved blade in the forge area. If you then compare that pic to the ones of the final blades at the end, you'll see that they're almost identical. The main purpose of the slurry at the end is twofold, firstly it hardens the edge (and as discussed may curve the blade a fraction more) but also it gives the decorative 'hamon' pattern to the steel which is unique to each swordsmith and also to each area of Japan. Mike Huntley, who was curator of Japanese swords at Sotheby's mentioned at the weekend just gone that you can tell who made the sword and from what area of Japan it came from, simply by looking at the pattern of the 'hamon' - Rob

 

[dh7892]

SometimeWoodworker,

I don't understand, you say: "There is NO curvature introduced into the back." but also agree with me when I say that there is curvature there even if it is small?

Also, if you have a flat back and then only lap 25mm of it, how can you not be introducing either a curve or a step change in gradient 25mm in from the edge? Of course the section you lapped will be flat (ignoring the hollow) but it will not be coplanar with the unlapped part.

As for what I meant about when you get to the deepest point in the hollow, I think I need to post some drawings or something in order to be able to explain it. I don't want to hijack this thread (any more than I already have!) so I'll start a new one when I've got some pictures.

I hope none of this comes across as bad natured or argumentative. I'm not trying to be cantankerous here; I just want to find out why our opinions differ (or if they are actually the same but we're misunderstanding each other).

 

[sometimewoodworker]

Dh7892

A misunderstanding and probably mis quoting. You change the taper on the back but it remains flat. And it is not, and doesn't need to be coplanar with the front

 

[GazPal]

If desired, I could suggest further reading regarding Nihon-to, as there seems to be a little confusion over the smithing process involved in their crafting, but the timescale taken to forge a blade does not amount to two weeks. Licensed smiths are limited by law to produce two sword blades per month/24 blades per year (Have been since circa 1953-54 when the occupying powers decided legalise swordmaking for the sake of craft preservation and for swords to be crafted as art objects and not weapons - swords and their manufacture were banned following the Japanese surrender in 1945). Swordsmiths also carry out other smithing work, unless .

With all due respect and having been involved in the study of Nihon-to for quite some time, Wikipedia actually provides a slightly more accurate representation of the smithing process, but there's much more information should you wish to know more via study.

 

[woodbloke]

I can see that we differ on this, but as I said, I was there and I did ask the man :wink: Best to leave it there I fancy - Rob

 

[SteveJ]

Jermone - the luck comment was intended tongue-in-cheek, nevertheless a great many of the greatest scientific achievements are down to luck over judgement, and I am certainly not one to down play the importance of scientific method having read physics at uni :wink:

From what I have read / seen in video the fundemental curvature is produced in the quench, the resulting shape is controlled by manipulation of the relative thickness and profile of the softer outer metal jacket. Varying the relative thickness of the two materials producing greater or lesser movement when the materials contract. Applied to chisels the shape of the back dictates how the tool warps when quenched producing the ura or hollow, and similarly the sweep in a sword. I've no doubt the degree of sweep is adjusted by some smiths following the first quench.

To produce a straight blade surely all that is required is for the harder steel core to run all the way through the blade front to back, (so long as the softer iron cheeks are balanced) as opposed to a sword where it does not extend all the way through to the back side. I was given to understand that in sword play the user aims to always block with the side or preferably the back of the blade so as to protect the hard cutting edge from chipping or fracture.

 

[GazPal]

I can see that we differ on this, but as I said, I was there and I did ask the man :wink: Best to leave it there I fancy - Rob

I've also been fortunate to visit Japan a few times over the years and met several smiths on a number of occasions, as I have a specific interest in Japanese swordsmanship and swords. :wink: Yet any information I offer appears to be have been discarded off-hand? I don't mind in the least, but it would have been a good opportunity for me to share the first hand knowledge I possess and provide information regarding further study.

 

[sometimewoodworker]

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.

Gary may be I am misunderstanding but I think you will find that while some knives do have one flat side, depending on the intended use, this is not the only traditional shape. There are many knives with a similar cutting edge to the sword, sushi knives are an example.

A good example of a knife with one bevel is the http://unioncommerce.co.jp/menkiriaokou.htm noodle knife for professional chefs that is only £1,500.00 :shock: you thought the wood working tools were expensive.

 

[GazPal]

Gary may be I am misunderstanding but I think you will find that while some knives do have one flat side, depending on the intended use, this is not the only traditional shape. There are many knives with a similar cutting edge to the sword, sushi knives are an example.

A good example of a knife with one bevel is the http://unioncommerce.co.jp/menkiriaokou.htm noodle knife for professional chefs that is only £1,500.00 :shock: you thought the wood working tools were expensive.

Indeed there are, but in terms of marking knives they tend to be sharpened/polished on one side of the blade. :wink:

 

[Harbo]

Bit late into the sword making as I didn't have access to my book "The Craft of the Japanese Sword".
According to that, initial curving is carried out by forging allowing for up to an additional 1/2" increase in curvature during the hardening processes.
Final adjustments are carried out by hammering the back edge to remove curvature or to increase it by touching the back on a red-hot block of copper then quenching,

Rod

 

[woodbloke]

Bit late into the sword making as I didn't have access to my book "The Craft of the Japanese Sword".
According to that, initial curving is carried out by forging allowing for up to an additional 1/2" increase in curvature during the hardening processes.
Final adjustments are carried out by hammering the back edge to remove curvature or to increase it by touching the back on a red-hot block of copper then quenching,

Rod

Interesting...thanks for that Rod - Rob

 

[sometimewoodworker]

Indeed there are, but in terms of marking knives they tend to be sharpened/polished on one side of the blade. :wink:

Now I understand. I thought as we had gone from planes and chisels to swords. You were taking us into the kitchen :lol: not back to the woodwork shop. And AFIK you are spot on. I've never seen a double bevel(that is on both sides of the blade) traditional laminated steel marking knife. There are some very nice modern ones where the blade can be retracted into the handle and locks with a nice brass screw.

 

[GazPal]

Indeed there are, but in terms of marking knives they tend to be sharpened/polished on one side of the blade. :wink:

Now I understand. I thought as we had gone from planes and chisels to swords. You were taking us into the kitchen :lol: not back to the woodwork shop. And AFIK you are spot on. I've never seen a double bevel(that is on both sides of the blade) traditional laminated steel marking knife. There are some very nice modern ones where the blade can be retracted into the handle and locks with a nice brass screw.

:lol: There was reason behind the madness.

Japanese blades are traditionally crafted with a right hand bias with hard steel to one side of the blade due - in part - to the old time insistence that everyone be right handed and the comparative rarity of iron sand within Japan. Traditional sushi knives are also single bevelled.

 

[Sawyer]

Thanks for the replies, everybody. Think I'll try to avoid hammering unless all attempts with honing/flatting fail to avoid the hollow meeting the cutting edge.

It is evident that Japanese metalworking technology is complex. Think I'll be sticking to western chisels and planes for the time being!

 

[sometimewoodworker]

Thanks for the replies, everybody. Think I'll try to avoid hammering unless all attempts with honing/flatting fail to avoid the hollow meeting the cutting edge.

It is evident that Japanese metalworking technology is complex. Think I'll be sticking to western chisels and planes for the time being!

The metalworking technology is complex but the maintenance and sharpening for the chisels isn't. It is a little different from the sharpening of a western chisel but not rocket science. You will be doing yourself a disservice if you let that stop you from at least trying a tool that many people consider to be much better.

Having almost no western (or any) chisels and living in Tokyo at the moment I gave them a try. I will be getting more before I leave Japan for good. They are very nice tools.