When the swap makes sense
A shinai has four staves, and in theory any one of them can be replaced. In practice, the question is whether the other three are worth keeping. If the bamboo is still green in colour, the fibres are uncompressed and there are no hairline cracks running toward the nodes, a single broken stave is good reason to open the weapon up and do the work. If two or more staves are splitting, if the grain has gone grey and powdery, or if the leather cap at the tip has been grinding an uneven seam for months, the whole assembly is already compromised. Replacing one slat while three others are quietly failing wastes an afternoon and a good piece of bamboo.
The donor stave must match the surviving three in species, wall thickness, and — crucially — the position and spacing of its nodes. The nodes, those solid cross-walls in the bamboo's structure, fall at different intervals depending on where a culm was cut, and a mismatch creates a stave that bears load unevenly along its length. It may also change the balance point slightly, which is worth checking before the cord goes back on. Because madake (Phyllostachys bambusoides) is the standard species, a replacement cut from a different bamboo — rattan, carbon or a lesser Phyllostachys — will behave differently under impact and may split faster than the originals.
The work itself
Disassembly starts at the tsuru, the tensioning cord that runs down the spine. Slacken it completely before touching anything else; a cord under load will spring the staves apart unevenly if released suddenly, and the leather cap can tear. Once the cord is off and the cap removed, the four staves are held only by the tsuba, the hand guard, and the nakayui, the binding cord near the midpoint. Slide both off, and the bundle comes apart cleanly.
Fit the new stave dry first. It should sit flush with its neighbours along the full length with no rocking at the nodes. Light scraping with a cabinet scraper is acceptable to fit a slightly proud surface; adding material to fill a gap is not. Re-assemble with fresh cord and a cap in good condition — there is no point reusing a cap whose leather has gone stiff and cracked. Check the balance point before the final tightening, because a heavier or lighter replacement stave will have shifted it. Once the cord is tensioned and tied, run a thumb along every seam: no daylight, no ridge, no movement. That is what done feels like.
Four Staves is an independent publication about kendo equipment and craft. It is not a federation, dojo or retailer, and offers no training instruction, grading or affiliation of any kind.