Carving a Tsuka

In this tutorial I will demonstrate how I carve a new tsuka core from scratch.  I want to first make clear that this is not a traditional method nor how I would construct a tsuka core for an antique restoration necessarily, but rather a method I use for the typical modern made production blade.  There is a lot of room for your own personal adaptations so you can follow this guide loosely and change it to fit your needs if you like.  Let’s face it, we don’t always want to spend more on having a new tsuka made than we did for the entire sword itself and you also might not have time to apprentice in Japan for 10 years to learn the traditional way, so here is a way for us regular Joe backyard cutters to give our beloved workhorse sharpies a new set of duds :lol:
Wood Type

Over the years I’ve pieced together notes and techniques gathered from different sources and eventually became comfortable with the blended method I will be detailing here.   I’ve also tried out a couple of different wood types and I have chosen to use American Yellow Poplar as it has what I feel is the best mix of characteristics for this purpose as well as being easily obtained.  Other wood species that are suitable besides Japanese Honoki are Magnolia, Alder, Ash, and Beech.

When choosing a wood type for this application you generally want to look for a tight and straight grain pattern as well as low acidity, moderately heavy, moderately low in shrinkage, moderately low in bending and compressive strength, moderately hard and stiff, and moderately high in shock resistance.  And one that does not produce sap.  

The wood should also be easy to carve and sand so try to avoid especially hard woods like hickory, certain oaks, Ironwood, and other similarly dense varieties.
Another important factor is price and I find that on average, enough good quality kiln dried Poplar for an average length tsuka runs around $3-$4. I try to get 3/8″  thick by 3-4″  wide by 12-24″  long boards when possible but most of the time 1/2″  thick is all that is available locally. Try to choose boards that are as flat as possible.
It’s very important that the boards you choose are free of knots or sugar deposits or any other structural flaws like cracks or fractures that could weaken the finished handle.
The Tools

Most of the tools I use for this process are ones I’ve accumulated over the years before I ever started working with swords and that many of you probably have in your garage or basement already. The most expensive one I use is the belt sander and it was on sale for under $80.

Chisels – I use a decorative wood carving, flat head chisel that I’ve slightly modified for most of the preliminary channel carving.  I refined the tip with a bull nose edge and bent the shaft at around a 30 degree angle to make carving a flat board easier on my knuckles.

I also use a few different sizes of standard wood chisels that you can get at any hardware store

Clamps – A variety of these can be used, from C-clamps to squeeze clamps or even cord or used ito is fine. Basically, anything that will maintain even pressure on the boards while the glue is drying.

Utility Knife – It doesn’t have to be anything fancy like a Japanese made kiridashi, I just use a standard razor and a sharp, all around utility.

Files/Sandpaper – Standard wood files, some 120 and 220 grit paper and a sanding block is all you need really. I have also started using a surform rasp, a small wood plane, and a table top belt sander to help speed up the process but use these with caution as they can remove a lot of material very quickly.

Ruler/Calipers – A pair of calipers can come in very handy and are available for as little as $5 but a ruler or tape measure will suffice. For about a dollar you could also pick up a non stretching fabric tape ruler in most craft stores.

Saw – Any small hand saw will work but if you have a band saw or scroll saw, go for it. I typically use a coping saw or a small electric jigsaw.

Drill – One of my most versatile tools is my beloved Dremel/rotary tool, I use it for so many things I’d be lost without it. I also use my cordless drill often but if you have a mounted drill press, that might be best option for you.

Needle/Jewelers files – These files come in very handy for so many projects of mine and I’m now on my second set since I’ve worn my first one out with use. They can be found for very little money in most any hardware store.

Glue – Last but not least, a good quality wood glue. I am a bit of a hardware store junkie and I have a problem with all the variety offered in the large stores so I’ve probably tried almost every wood glue available in the US and at least one imported from Australia.  I look for one that dries very quickly but allows you enough time to position, is tough as nails, and takes heavy impact well.  Waterproof is also a good feature.  Really, any good wood glue should be fine.  Don’t use glue that expands as this can seep into the channel and don’t use white craft glue because it’s just not strong enough for this application.

Completion Time
The time needed for this project, excluding drying time, will be anywhere from 2 hours for those rushing and satisfied with “eh, it’s good enough” to about 6 + hours for OCD perfectionists that just don’t know when to quit :oops: (I’ve taken more than 30 minutes just picking out the boards sometimes, lol)
So plan accordingly ;)
Step 1 – Choosing grain direction and laying out lines

It is important that the grain structure flows out from the ha to the mune and away from the center because in short, the force of impact could possibly crack the core if the grain flows the opposite direction.  I have illustrated the hard to see grain lines in this example.
(ha side being the top of the photo)

Take your time aligning the nakago on the board and take note of the flow from the saya because when possible, you want this flow of shape and angle to continue into the tsuka.  Once you’ve decided on the positioning go ahead and mark out the edges of the habaki and koiguchi, and then trace the shape of the nakago including the mekugi-ana and continuing shinogi if applicable. (I forgot to trace this on the first board initially but added it later on)
The base of the habaki should be pressed up against the edge of the board even though there will be the later addition of the tsuba, seppa, and top of the fuchi.

Then draw an outline continuing from the edge of the saya down to the other end of the board just to give you an idea of the tsuka’s finished width/thickness.  The fuchi will actually be what determines the final dimensions of the tsuka.

Extend the outline about a 1/4″ at the end of the nakago and add a secondary set of lines about a millimeter inside of the traced outline since you want the fit to be tight.
You should now have a complete nakago outline represented on your first board.

You should also have an idea of the depth you need to carve from the side view so use calipers or a ruler to transcribe the thickness of the nakago to the edge of the boards. 

Step 2 – Scoring the outline

With your utility blade, very carefully score the inner outline.  The score on the mune side should be approximately 2/3 the mune’s total thickness and the ha just about the total thickness(explained below) so you may have to do this more than once to get the score deep enough.  Go slowly and make sure your fingers are far from the path the blade will take because the blade can jump.

Step 3 – Carving the channel

Once you’ve scored the lines you will begin carving the channels.  First clamp down or otherwise secure the board on a stable surface.  One side of the core will be carved deeper than the other because the nakago should be sitting on solid wood rather than the middle of the seam.  Some techniques call for carving the entire depth on one board while using the other as just a cap but I like to split the difference at about 2/3.

Then start near the edges and go slowly while not placing a lot of pressure on the chisel.  Make sure your chisels are honed and very sharp and free of burrs so it will remove the material easily and smoothly.

Always remove less than you think you need to and check your progress often by placing the nakago on the board because while you can always remove more material, it’s much harder to replace it.
Keep going and constantly check the fit until the nakago slides in and out of the carved slot freely but without any play.  If you need to widen the channel, you can use a metal straight edge and your utility knife to carefully cut the edges.
You can use carbon paper between the nakago and the channel to see where the high spots are or sometimes I wet the nakago and use some crushed charcoal powder for this.

I feel it’s worth saying again so….constantly check your fit.

If you’ve somehow removed a bit too much and there is a wiggle when the nakago is inserted, don’t panic it’s not the end of the world.  You can add some wood veneer shims before the boards are glued, which will be every bit as good as the original wood and is commonly used to adjust fit.

Once you’re finished it should look like this

Now do the same thing on the other board using the opposite side of the nakago.

Step 4 – Drill a pilot hole for the mekugi-ana

Later on in the process you will be properly sizing the mekugi-ana but for now you just need a small pilot hole so you can locate it later when the boards are glued together.  With a drill or Dremel, use a small diameter bit and drill a hole in both boards.

Step 5 – Transfer the position of the nakago

Before you start shaping the core you need to know where the nakago lies so you don’t get too close to the edges.  This is much more difficult and less accurate if you try to do it after the two boards are glued together so we will do this before we glue.
Simply record the distance from the edge of the boards to the edges of the channel and apply them to the other side then place the nakago within the guide marks and trace the shape.
You might want to make a paper template of the nakago shape which you can use to re-apply the outlines later on once you’ve started filing and sanding the core.

Include the marks for the habaki and saya

Step 6 – Glue and clamp

Spread an appropriate amount of glue on the flat surfaces of the two boards. (make sure they are clean of sawdust or dirt)

Slide the nakago into the slot a few times to make sure everything is aligned properly. You should make sure there is no excess glue seeping into the channels and if there is, you should clean this out before you clamp the halves together.

If all is good, go ahead and clamp or tie up the two halves tightly, making sure all areas are making contact.

Let this set and cure. Drying times can vary so follow the directions on the glue.

Step 7 – Cut off excess material

Once the two halves are fully set, remove the clamps and proceed by cutting off excess material using band saw or hand saw. It’s ok to cut at the lines because your finished core will be thinner allowing room for samegawa and or ito.

Step 8 – Shape for fuchi

Before you start shaping the core you want to make sure that the fuchi fits properly as this will be the guide to how much material you will need to remove. Fitting the kashira will come a little later.
Start taking off a little wood from both sides and both ends but go slowly.  Don’t worry if you wind up removing a little too much, we can fix that later on by applying some veneer but still try to avoid this.

I use a pencil or marker to mark where I need to remove more material as I go.

You want to extend the neck down past where the fuchi covers it since you will be removing some of this length later to compensate for the thickness of the tsuba, top of the fuchi, and seppa.  So the fuchi will wind up being a little lower than it is now.  The reason I do it this way is because one of the biggest mistakes you can make is that you remove too much wood from the top creating a gap in your fittings. You want to go slowly on many steps in this process and I find that this one is especially important.

Step 9 – Shaping the core

Now that your fuchi fits snugly you can begin removing material from the length of the core. In the beginning you might want to use the surform rasp or wood plane or belt sander too make things go a little quicker, but be very cautious because these tools can remove a lot of material very quickly, especially power tools.

Remember to retrace your nakago shape or otherwise indicate it’s location while you’re removing material and erasing the outlines.
At this point you will be sizing the core for the additional thickness of the tsuba, etc. With a pair of calipers or ruler, determine the accumulated thickness of those pieces, making sure to include the thickness of the top piece of your fuchi (usually about a millimeter) and then transfer this measurement to the top of the core.

Remove the appropriate amount (again, take it slow and remove a little less than you should, check the fit, and then remove the rest little by little with a file or sandpaper) and with the fittings in place, fit the core onto the nakago and proceed to finish shaping the mekugi-ana.  I like to finish the mekugi-ana together with removing the last of the wood from under the fuchi, and I repeatedly mount and remove the core from the nakago as I go to check the fit.
Go slowly using a round needle file and constantly test the fit of the mekugi. The bottom of the hole in the core should be just about a millimeter lower than the bottom of the hole in the nakago because you want there to be a little pressure pulling the nakago into the core when you insert the mekugi in.
Over time this fit will loosen and you want some extra room for tightening, this is also why we’ve added a little room at the bottom of the nakago channel.

Once the mekugi-ana is shaped and finished, you should measure for the placement of the kashira.  I measure the width of the ito I will be using while it is stretched tightly and then mark in increments down the length of the tsuka on the edge of both the ha and mune sides.
To have the end knots come out on the correct sides(omote and ura), there should be an odd number of increments leading to the rim of the kashira when you’re done.

Once this is done you can fit the kashira, including cutting out the slot where the ito will pass through, and then go back to refining the shape of the core. I use a coping saw and needle files to shape the slot in the kashira end.  It is better to have a little more material at the end of the tsuka rather than the two skinny “posts” found on many production tsuka because it will protect your kashira from denting when putting the tsuka back on, especially cheaper, thinner kashira.

When shaping the core, pay attention to the shape from all sides by constantly stopping and holding the core at an angle. Make sure you have good lighting so you can see even subtle adjustments that need to be made.  I also run my fingers along all sides because they can pick up what my eyes might miss.

Your final shape will depend on what style you’re going for such as morozori, rikko, hiachi, or other, but despite the style there should be enough room for samegawa or ito or shims… or all of the above.  Too often people wind up with a finished tsuka that is too fat and the ito is sitting higher than the rims of the fuchi and kashira or they will almost be round because they are too beefy.  Tsuka cores should be relatively thin and flat on the sides while having nice slender oval edges. The rest of the thickness on the side that will give the tsuka it’s overall slightly oval shape will be provided by the folds of the ito and the hishigami.

Step 10 – Carving the ramps

In order for your end knots to sit properly and not stick out too far like they do on most common production tsuka, you will need to carve ramps near the kashira.  The length and depth of these ramps are determined by factors such as the type of ito you are using and the style of the kashira, as well as the thickness of the samegawa.
For typical 10mm silk ito the ramp on the omote side will be approximately 17-19mm long depending on how tightly the ito is wrapped or just about two increments up from the kashira rim. If you are placing the emperor’s node in the first open diamond from the kashira, you want the ramp to start just after that node.

On the ura side you will start the ramp a little higher up at around 20-22mm from the kashira rim or approximately two and three quarters increments up from the kashira as this will be where the top of the knot will fall.
If you will be using samegawa, whether full wrap or panels, remember to allow for the thickness of the skin and remove the appropriate amount of material.
When you’re done it should look similar to this

Remember to make sure you’ve removed enough material by using pieces of the samegawa and ito you will be using to check.  I have a small rectangular strip of samegawa of moderate thickness that I use to wrap around the collar and and a thicker piece at the butt end of the core and I then wrap a piece of ito over this to see if it aligns where it should.  I also give a little extra room for the paper strips I use prior to tsukamaki.  Don’t remove too much where you’re too close to the nakago but you can always build up the size later on.
I always let it sit for a day or at least a few hours after I think I’m done and then come back to it because with fresh eyes, I usually find some spots that need a little refining.  Once you’re satisfied, slide it back on the nakago with the fittings and make sure everything fits nice and snug.

If you’ve removed a little too much from the parts under the kashira or fuchi you can glue small strips of a thin wood veneer such as this

until the area is built up enough for a tight fit. This core was made to receive a full wrap of premium samegawa but if yours will have panels instead, you would have removed a little less material from the circumference and would now proceed with carving channels for the panels to sit in. You would make these wide enough so there won’t be any wood showing on the sides after the tsukamaki (start about 1/4″-3/8″ from edges) and deep enough so the skin sits flush with the rest of the surface (about 1- 1 1/2mm).  Try to keep the width of the channels evenly spaced along the length if possible.
Well, that’s it! Good luck on your project. 

If you’ve enjoyed the tutorials and feel like buying me a cup of coffee, a meal or more tools, I’ll be super grateful. Thanks!

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