...And that's all the history I've got for you. It's a pretty straight forward concept. A few notes on the form and function of the Fukuro-Shinai....
The FS differs significantly from the much more well-known, modern Kendo shina. It is made of one piece of relatively light bamboo (as opposed to the heavy, overlapping layers used in a modern Kendo shinai) and it is padded with cloth and leather. The Kendo shinai is stiff and heavy and can cause some serious bodily harm if a good blow makes contact -- which is usually not a problem because modern Kendo practitioners wear heavy armor or Bogu. The Fukuro-shinai is designed for full contact work in normal dojo attire. It can still cause injury and you will definitely feel it if you catch a good strike, but it is unlikely to send anyone to the hospital.
I would like to say right off the bat that the Fukuro-Shinai I made is not a historically accurate training tool. It's also probably not kosher in a lot of dojos, depending on how traditional your instructors are. If you're interested in taking the extra steps to make it accurate (i.e. real leather, different handle wrap, more natural materials), it shouldn't be very hard to figure out.
Also, while I'm at it, please do not stab, burn or impale yourself while following this tutorial. Additionally, do not use your completed fukuro shinai outside of a fully consensual training situation. People don't like being hit with sticks without their permission. I take no responsibility for any physical or emotional harm caused either during the following of this tutorial, or as a product thereof. Etc. Etc.
Still with me? Let's do this.
Step 1: Selecting Materials
Okay, first you need one piece of quality bamboo, a little bit longer than the total length of the that sword you want to make. Bamboo is 90% of the shinai, so choose wisely. Ideally you will want fresh bamboo that can be dried for at least a month (tends to be more flexible), but you can use the commercially available bamboo that they sell at garden centers in a pinch. The latter is kiln-dried, which makes it brittle sometimes, but it should work. Make sure you get a very straight, solid-feeling piece (give it a little bend to test for brittleness if it's pre-dried), about 1-inch in diameter. I happened to know where some very good bamboo was growing wild a few towns over, so I went and harvested it, then dried it in my attic for a few weeks.
Note: most Fukuro-Shinai are straight but I decided to use a natural curvature in the bamboo I had to give the blade a little sweep by the tip. This is mostly an aesthetic thing, but it also helps to keep me mindful about which side is the cutting edge.
Next you'll need some leather or vinyl for the characteristic "fukuro" padding. I'm cheap, so I went with white marine vinyl, which is about $9.99 a yard, very supple and has a soft, padded feel to it. There are lots of colors to choose from, but white is traditional.
Black electrical tape
1 meter of cheesecloth or muslin.
10-20 feet of 550 paracord, or leather cord.
"Shogun Assassin," "7 Samuarai," or "Yojimbo" to watch in the background
Tape measure or ruler
Sewing machine or needle and thread
A rotary cutter or sharp knife for cutting leather/vinyl
Step 2: Split the Bamboo
The size you make is largely a matter of personal taste. You can make anything from a Tanto to an Odachi, but I chose to make a Wakazashi length, which for me means a 7 inch handle, 22 inch blade.
2. Next, go to the end that will be the tip of your sword and divide it into eight parts with your felt pen (cut it in half, then in half again horizontally, then diagonally, then the other diagonal).
3. Measure from the bottom of the sword and mark the place where the handle will end and the blade will begin. Wrap this tightly with electrical tape to keep the bamboo from splitting too far.
4. Place the blade of your knife along the first set of marks that you drew. Give the back of the blade a firm strike with the palm of your hand to split the bamboo. Only split about 6 inches down, or to the first knuckle you come across. Do this three more times until all of the splits have been started. Now begin running the knife down each pair of splits, driving the splits further down towards the handle. Try and keep them all even, rather than splitting one all the way down to the tape at a time -- they will come out much more even this way.
If you come across a knuckle, drive the split as far as it will go easily, then use your palm or a piece of wood to strike the back of the blade and force the split through the knuckle.
5. Stop splitting a few inches before you reach the electrical tape. If you drive the knife all the way down, the split will overshoot the tape and go into the handle.
Step 3: Pad the Bamboo
2. Next cut a piece of cheese cloth about as long as the length of your blade, plus 3 inches, by about 2 feet (e.g. for my wakizashi, 22 +3 = 25 inches by 24 inches). This will be wrapped around the bamboo to add some extra padding.
3. Wrap the cheesecloth loosely around the blade portion of the bamboo, leaving about three inches extending past the tip. Lightly wrap electrical tape around the bottom and middle of the cloth to hold it in place (note, I used masking tape for this. It doesn't matter very much as you only want to keep it from unraveling)
Step 4: Lay Out and Cut Your Leather Sleeve
2. Use a rotary cuttter, exacto or leather knife to cut out the leather sleeve.
3. Now turn the leather side away from you so that the fuzzy, padded side faces out. Fold the leather in half around the sword (leather facing IN so that when you turn it inside out, the seam doesn't show). You can hold it in place with pins, but I recommend taking a piece of wide masking tape or packing tape and using it to tape the entire length of the seem together (not shown in pictures. actually, in the picture I have the leather facing out -- don't do that). This helps to keep the material from bunching up as you sew it.
4. Next mark where you are going to sew the seam. Pinch the sleeve down so that it is tight around the bamboo on the inside. This is your bottom line (i..e if you sewed it here, you would have a perfectly tight sleeve that could not be fitted over the bamboo). Add about 1/2 inch to the place that you pinched the sleeve and make a mark. This is where you will sew your seem. The measurement will be different for everyone, and actually a little bit more than 1/2 is probably fine, but you don't want the sleeve to be so tight that it doesn't fit over the cloth wrapping.
Step 5: Sewing the Sleeve
1. Set up your sewing machine. If you're doing it by hand, stretch out your fingers and massage your carpal tunnels.
2. Turn the stitch length way up (I used 4.5) and the tension way down. The leather is very thing and doesn't have the same kind of thread-level tensile strength that most cloth does, so it will bunch up and tear if you use small, tight stitches. This goes for hand stitching as well.
NOTE: Make sure the fuzzy side is facing out!
3. Stitch from the bottom of your sleeve up to about 1 an inch away from the top (depending on how much extra you cut your sleeve. You want it to extend about 1-2 inches past the tip of the bamboo ultimately) , turn the sleeve at a right angle and sew up the top all the way to the folded edge. Back stitch to lock it in, cut the thread. Bam. Done.
Step 6: Inverting the Sleeve
2. Starting at the bottom of the sleeve, roll the leather inside out so that the leather side is on the outside. This may be difficult because of how tight the space is inside, but go slowly, be patient, and most importantly don't tear the seam or the leather. Marine vinyl has pretty poor tensile strength, so don't over stretch the material. You can use the blunt end of a chopstick to help push from the inside, especially when you get all the way out to the end and need to pop out the corners.
Step 7: Fit the Sleeve Over the Bamboo
Step 8: Finishing the Sleeve and Wrapping the Handle
VERY IMPORTANT! The seam is considered the spine ((i.e. the dull side) of the blade. If you are using a curved piece of bamboo like I am, make sure the sleeve is oriented properly before you fix it in place with tape/cord/whatever.
Make sure you leave a little bit of extra sleeve up at the top -- the more padding you have there the better because the bamboo will still be quite rigid when it comes to stabbing/thrusting. If you hit yourself with the fukuro-shinai at this point and it feels a little bit too stiff, you can break it in a little bit by flexing the blade portion a few times. Don't go crazy and break it, but it should be able to bend about 15-20 degrees without breaking.
Wrapping the Handle
This is optional, but recommended for a polished finish. If you want to get fancy, you can really go wild. You can use flat cord and do a traditional tsuka wrap, try your hand at coxcombing/ring-bolt hitching or go with any of the myriad paracord wraps out there (I recommend Stormdrane.blogspot.com for ideas).
I did a simple turk's-head knot (http://www.troop54.com/knots/TurksHeadKnot/TurksHeadKnot.htm.) covering the electrical tape at the tsuba, then left a long tail which I wrapped tightly around the handle down to the knuckle (which made a convenient knocking point for the wrap), then back up around. I tucked the tail under the original wrapping and into the turk's-head knot, then melted the end to keep it from slipping out. If you want to go with this method, I recommend using a marlin spike or an awl to help open up the turk's-head knot at the end to accept the tail.
Last but not least, test it out (in a consensual training environment). Train, improve, repeat.