Why a shinai?
The "singlestick" or "cudgel" was a traditional training tool for the practice of English backsword, as well as being a weapon in its own right. Sporting singlesticks were made from light ash saplings, kept soaking in a trough of water to keep them flexible, and given leather or wicker basket-hilts. Armour consisted of a masked fencing helmet for the face and head, a long-sleeved leather jacket or padded coat, covered with a thigh-length leather apron or bib for the body and cricket pads for the legs. Earlier cudgels were made of solid wood and the only protective equipment used was "the old North-country prayer (beautifully terse), 'God, spare our eyes!'".
Unfortunately English ash is not available worldwide, and even if it were these weapons have some disadvantages as training tools. If they are light and flexible enough to be completely safe they are poor substitutes for real swords, and if heavy and solid they require nearly as much armour as for steel blunts, and because a stick does not flex thrusts can be even more dangerous than with steel, so to some extent you may as well use steel.
Although the shinai is not historically accurate for English swordsmanship, it is a far superior sword substitute than a simple stick. Because the shinai flex in all planes, they are inherently much safer than solid wood, and slide and bind very like a steel sword blade, rather than "bouncing" like solid wooden wasters do. They come in a variety of sizes, are relatively cheap and easily modified, and are commercially available worldwide.
We initially adopted shinai as a bouting tool for the practice of English bastard sword, but have found them excellent as backsword wasters. Although the overall weight of the weapon is considerably less than a real sword, the combination of cutting the handle short and adding the weight of the basket and pommel, makes them handle remarkably like a well balanced backsword. We find them suitable for both Silver and traditional English backsword / military broadsword; with different fittings they would probably be good for Italian sidesword and German messer as well. Curved shinai (designed to simulate the katana) are also available, and make cool sabre wasters.
You will need:
A size 39 is about right for an adult male, but smaller sizes can be used for women and juniors.
A basket hilt
Traditionally these were made from leather or wicker. We tried wicker baskets and destroyed them very quickly. We then adopted Tony Wolf's suggestion of using plastic mooring buoys as hilts; 6 inch buoys are sufficiently large for anyone's hand, but for people with small hands you can use anything down to a 4 inch buoy, as long as the hilt is offset on the handle to make a little more room on the right.
Something to bind the shinai together
Shinai are constructed from four lames of bamboo, held together by a small internal razor blade at the very end, and a leather wrapped handle. Because we will be cutting the handle short, this may compromise the structural integrity of the shinai, and you will need something to hold the four lames tightly together. You could use a short section of metal pipe of appropriate diameter, but in this case we found some metal caps that were just the right size to hammer over the handle. You will also need a large screw to screw into the end.
Something to make it pretty
I like to cover the mess at the pommel end with a rubber stopper, partly for aesthetic reasons, and partly for safer pommel-bashing.
Make the hilt. Drill a hole at each end, right through the middle, just big enough to fit the shinai handle through. Then cut a hole out of the top big enough to fit your hand in and make full wrist movement through (an electric jigsaw is good for this). Be conservative - remember you can always make it bigger later, but not smaller! Also note that the hand hole is close to the back hole (where the pommel will be) but you must leave quite a big space above the front hole (where the blade will be). (The little hole in this picture is the remains of the hoop on the buoy, which I am using as a bit of a quillon here. Others like to keep the loop on, or discard it entirely).
Put the hilt on the shinai. Shove it all the way through, then cut the handle off an inch or two from the basket.
Make the pommel. Jam whatever you are using to secure the lames over the end of the shinai, hammer it down good and tight, then screw in the screw to really tighten the whole thing up.
Neaten it up. Put the rubber stopper over the pommel. Use a file, sandpaper or even a cigarette lighter to round off the rough edges of the hilt.
Additional modifications you can make include:
Squaring up the handle. Unless you can afford an oval-handled shinai, you will find the hilt may spin during bouting. One way around this is to wet the handle leather, and then insert long thin lames under the leather of the handle to make it squarer before putting the hilt on, and adjusting the hole in the basket appropriately for a tight fit. Use plastic card (available form model making shops) because metal strips will wear through the leather eventually. You may also try gluing the basket in place, though this will kake it harder to swap fittings when the shinai eventually wears out. None of this is 100% effective, and some "spinning" must be expected.
Taking off the yellow string and gluing the tip and C.O.P. leather wrapping bit in place – the yellow string does serve to mark the back edge, but also comes loose occasionally and must be retied.
Adding a soft thrusting tip. We don't find this particularly important, but may be worth the effort if you want an extra measure of safety.
Decorate the basket. Yellow baubles aren't terribly attractive things by themselves. The following model was made to order for a member of the Finesse Academy of Fence in Canberra.
Hit each other with them. We have abandoned padding for backsword-shinai use, and wear only shirts / jackets, fencing masks, gloves and a box. It is not pleasant to be hit, but the welts are good encouragement to defend yourself properly!