Re: Fukuro Shinai Construction and Usage
In Shinkage Ryu, most folks split to eight slats somewhere between 1/3rd and 1/2 of the way down. You can certainly split to 16 slats if you have the time, dexterity, and inclination, but it's not strictly necessary.
You should always sand the knobs down, even if they don't stick out too much. There's one tool, I'm totally blanking on the name for it, but it's a block of wood with a straight blade across it, at about a 30-45 degree angle. These are very good for smoothing out the knobs, as well as rounding off the ends (both the tip and the "tsuka-gashira" should be rounded off). Also, use an exact-o-knife or other small, thin blade, and round off the inner edges.
After splitting the bamboo, take your knife (I use a tiny saw for this), and cut away the inner remnants at the knob. Then use your knife (or a piece of glass) and smooth out all the sharp edges you can, on the inside and outside of the slats. Round of the tips, too, if you can. I also like to give the slats a once-over with a file to get them nice and smooth. Edges on the slats will destroy the fukuro you spent so much time making, so rounding them off is very important. If you can get a rounded trapezoid shape, that's the best.
After that it's complete. Treat the slats with oil or wax. I use a candle. And it's ready to go. The better you hit with it (energy coming out at the kissaki, striking/defending only with the mono-no-uchi), the longer it will last. With frequent use the take will start to curve, so rotate it in the fukuro. The slats will also start to twist. One person I know uses round wooden washers to keep the slats in line when the shinai is in storage. Once you round off the edges, the slats won't fit together like when you first split the bamboo.