Kozuka- basic contsruction, "How to make a kozuka", for Tom Options

[Guest_ford hallam_*]

The basic construction of a Kozuka.



The word kozuka means literally; small hilt, (ko-tsuka) in Japanese. It refers specifically to the rectangular metal handle of a small utility knife which is usually carried in the scabbard of the Samurai long-sword, or katana. Of all the various metal fittings that make up the mountings of Japanese swords the kozuka is probably the most standardized in terms of its dimensions and proportions. You may encounter versions which fall outside the norm but the following measurements, which are an average of over 100 examples that I have personally measured, can be taken as a starting point.
Length 95.6mm Width 14.3mm Thickness 4.7mm.
In reality you will most likely only find a deviation of no more than 1mm. Kozuka are usually made of material of about 1mm in thickness and are hard (ie; silver) soldered. All soldering is usually carried out before any decorative work is begun. The blades of kozuka are usually held in place by having the tang slightly bent so as to provide a sort of spring fit. Occasionally, paper is wrapped around the tang to provide additional friction.

The following is a brief description of one method of constructing a kozuka.
Begin by cutting a rectangle of metal sheet slightly longer that the desired final length and width. To copy the example that follows you can prepare a 1mm ( 1.2mm would be safer as it will allow you more freedom to create a fuller, more pleasing form) thick plate, 97mm long and 25 mm wide.

Have a look at the images of the real kozuka I've posted and give the whole sheet a similar curve across its width. Mark out 2 parallel lines, 14.3 mm apart and equidistant from the long edges. Either file, or chisel a 90 degree groove along these lines. These will allow you to bend the sheet accurately, and neatly, to match the profile you need. I usually mark additional lines on either side of the main one to indicate the final edge of the “V” groove. Make the groove as deep as you can without actually cutting through the plate and make sure you’ll have enough material left to shape up the outside when finished. This is simply a matter of personal experience I’m afraid and depends on how accurately and carefully you are able to work. Before you bend the sides up, file, or chisel a lip along one of the ends. I chisel the lip when I do this but if you need to file this feature it would be easier to do before the sheet is curved. I cut it to half the thickness of the sheet and make it 2mm long. Excess can easily be filed off once the end piece is soldered in place. This will make a seat for the butt cap later and while well worth the effort, is not absolutely necessary.
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Bend the sides into position keeping them parallel to each other but remembering that the face of the kozuka must slope to one side. At this point it's probably best to run some solder along the newly created inner corners as they may be quite weak.
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The next step is to cut and file the sides to the required height. In this case the back plate will be simply soldered onto the sides without any clever stepped joints or similar tricks. I’ve subtracted the thickness of the back plate from the desired final thickness of the two edges and cut the sides accordingly. The back plate should also be given a gentle curve and the edges of the sides which it will join to should be filed to match. Notice which side is the highest, and it’s relative position to the end with the recessed lip. ( the shaded bit at the back)
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This last diagram shows the back plate soldered on and the end filed neatly level and at 90 degrees to the length of the kozuka. At this point the ledge for the end cap insert is visible along the 3 sides of the front of the kozuka construction. Depending on how much you want to curve the end of your kozuka, cut out and shape a fillet of metal of suitable thickness ( 1.5mm should suffice for the usual degree of shaping) to fit snugly into the end and solder in place.
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This enlarged image of the butt of an antique kozuka illustrates one approach to the subtle shaping of the basic profile. You will also see versions that are far more angular
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These views of a kozuka show well the gentle curves of the finished form. In this case the design is vertical and the tang of the blade would be inserted in the top. Although the top edge appears curved from this point of view it is actually perfectly horizontal and flat. The last point to consider in the final shaping of a long narrow form like this, is applying entasis.
Ensuring that the middle of the form, when viewed from the front, is ever so slightly wider than the ends. This very subtle shaping counters that optical illusion of narrowing in the centre that is seen on perfectly rectangular, long and narrow shapes.

[Guest_ford hallam_*]

These 2 images show; the front and back of the same kogatana ( the blade of a kozuka )
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and a closer view of the tang.
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The polished face of the blade is completely flat and when fitted into the handle corresponds to the back of the kozuka.


I hope this helps, regards, Ford

[tsterling]

Excellent tutorial, Ford! Thanks! I didn't realize kozuka top faces had a curved profile (viewed end on), and I would never have thought of the 45 degree cut and folds.

[wunderlich]

Thanks Ford,

no need for me guessing strange things on kozuka anymore.

This is a great tutorial!!!

Karl

[Dick Bonham]

Hi Ford,
Thank you for a Great tutorial. Lots of stuff I didn't know. Any chance of a tutorial on carving Japanese characters?
Dick

[Guest_ford hallam_*]

Hello Dick,

carving Japanese characters is fundamental to kata-kiri and as such is quite a big subject. I'll do a basic calligraphy / carving tutorial soon.

Ford

[Phil White]

Ford,

This is great stuff. I would not have thought of the 45% cut either. I would have just formed it around a steel mandrel and hoped for the best. Great idea, that will have future applications in other things.

Thanks,

Phil

[Greg Obach]

excellent post
i've never seen this kind of knife but now i'm totally stoked on it...

thank you
Greg

[Janel]

Details, details. Ford, did you say a 90° angle? I see reference to 45° angles in the subsequent posts, and worry that I either missed something...or folks will learn the hard way that a 45° angle will only fold so far...

Have a look at the images of the real kozuka I've posted and give the whole sheet a similar curve across its width. Mark out 2 parallel lines, 14.3 mm apart and equidistant from the long edges. Either file, or chisel a 90 degree groove along these lines. These will allow you to bend the sheet accurately, and neatly...

[Guest_ford hallam_*]

Hi Janel,

yes, you're absolutely right, the "V" shaped channel should have a 90 degree angle at the bottom. Only then will you get a right angle when you bend the sheet up. I use a chisel which I've shaped to exactly that angle. It would obviously work for other angles too. In the jewellery trade we sometimes used to use a "v" shaped scraping tool of sorts, to score a line to create a similar effect.

Regards, Ford

[Karl Carvalho]

Aloha Ford,

I used the same scoring technique when forming bends in decorative metal laminates (aluminum, copper) for commercial displays. The hand tool comes from the high pressure laminate (Formica) trade. A little inserted carbide chip at the end can be shaped to need. With a straight edge, it can be quite effective.Here's one.

Karl

[Phil White]

Sorry for the confusion about the 45%, my bad. I really don't know why I didn't think of this technique, since I have done the same thing with wood, making Northwest coast style bentwood boxes.

Phil

[remo]

Hi Ford,

I try makera kozuka, the font in iron and the back

to solder iron on brass , whats is the beter solder composition ?

Thank's remo

[Guest_ford hallam_*]

Hi Remo,

very good question , when soldering iron or steel you can get good results with standard Jewellers silver solder. Try to use a flux that is made especially for ferrous metals though. The standard Jewellers flux and borax burn out and get too dirty too soon, before the solder has had a chance to flow.

hope this is clear.

best regards, Ford

[wunderlich]

Hi remo,

when soldering iron try to reach soldering temperatura as fast as possible! Even with a special flux iron will oxidise quickly in heat. Tying the pieces to be soldered with binding wire might be a good idea also.

Karl

[remo]

Hi folks,

Thank's for the tips,

Remo

[remo]

Hi Ford,

Some questions


The carving work is made before close the back ?



In the picture of your post nº 2 there are the fornt in 2 colors is the same metal carving and inaly gold (kemboo?)))or 2 distinct pieces?


Today a try make 2 kozukas for learn one in fornt in iron and back in brass ( as you an the Karl talk is realy more dificult to solder )
the other front in brass and back in coper.

Thank's

Remo

[Guest_ford hallam_*]

Hi Remo,

You can do the carving on the front before you solder on the back, I don't though, I complete the basic kozuka first. I then slide a steel former ( or mandrel ) inside the kozuka to support the shape while working on the outside. The kozuka is best held in a pitch mix in a bowl of on a heavy wooden board. There is a thread on this forum dealing with pitch. here's a link.

The kozuka you are talking about is iron front with a shibuichi back. The small section of gold is thin foil attached most probably by nunome zogan or fused with mercury. Kimboo is a Korean technique of fusing gold to a non-ferrous base. There is a possibility that the Japanese artists used a similar technique but so far I have no evidence. Personally, I believe that it was probably a common method in Japan in the past.

Good luck making your kozuka today. You should not have too much difficulty with the soldering. Use the highest melting point solder for the first soldering, and use the lower melting points for the following joins.

I'm sorry I can't write in Portuguese and I hope you can get the basic details I'm trying to explain. If something is not clear please ask me again. I'm sure there are many people who don't speak English as their first language who find this English based forum a bit difficult, but we will do our best to help each other and find ways to communicate more clearly. I also hope that this will encourage more non-English people to join us here.

I look forward to seeing your shiny new kozuka soon

Sorte boa e os desejos muito mais melhores. ( I hope that came out correct )

Ford

[wunderlich]

Today a try make 2 kozukas for learn one in fornt in iron and back in brass ( as you an the Karl talk is realy more dificult to solder

Hi remo,

one more thing. When you soldered your iron pieces it is very possible that the solder didnt flow through the whole seam.
Pickle this in a 10% sulfric acid bath. (not possible with stainless steel) ( use always fresh pickle- try to avoid much cupric salts in the bath- there will be a layer of copper on the iron anyway but it is not that much with fresh acid. The cupric residue has to be removed before trying to patinate the iron).

After having a clean seam again - reflux and than soldering again.



Ford, thanks for encouragement for non-natve english speakers.
Karl

[Guest_ford hallam_*]

Hi Karl,

you're more than welcome , I genuinely hope that we can become real global "tribe" here.

Thanks to you for the soldering pointers, It is so easy to lose sight of all the different aspects that need to be covered. Any chance you might be able to do a soldering/construction tutorial? pm me if you have any thoughts on that.

cheers, Ford