Japanese Sword Troubleshooting: Saya Rattle, Loose Mekugi, and Stuck Koiguchi

Saya-nari — Understanding and Addressing the Sound of the Blade Moving Inside the Scabbard

When you gently swing a scabbard and hear a "clack-clack" sound, this condition is called saya-nari. This occurs when there is a gap between the blade and the inside of the scabbard (saya-ki), with the primary causes being contraction of the saya-ki due to humidity changes or internal wear of the saya-ki from years of use. If left unaddressed, the blade will continue to move minutely inside the scabbard, causing scratches on the blade surface and peeling of the lacquer inside the scabbard.

The first thing to check in addressing this is the humidity environment. If saya-nari becomes prominent in winter when drying increases, returning humidity to around 50% may naturally resolve the issue. As a temporary measure, you can insert a few sheets of thin paper near the koiguchi of the scabbard to restore contact between the blade and the saya-ki. However, this is only a temporary measure, and fundamentally you need to commission a saya-shi to re-plane the saya-ki and readjust it to the proper interior diameter that fits the blade perfectly through "interior scabbard planing adjustment." Especially for valuable blades, self-administered temporary measures risk damaging the interior, so we recommend consulting a specialist early.

Mekugi Looseness — The Importance of the Small Bamboo Peg Connecting the Handle and Blade

The mekugi is a small bamboo peg that passes through and fixes the handle and nakago, serving as an extremely important component supporting the overall stability of the blade. When the mekugi loosens, the blade becomes unstable within the handle, potentially leading to serious accidents during iaido or test cutting. During routine inspection, grip the handle and gently move the blade up and down to check if you feel any "clatter." If you notice any irregularity, always inspect the condition of the mekugi.

When removing the mekugi, use a dedicated mekugi remover. Do not strike it out forcefully. Check the removed mekugi for cracks, deformation, or wear, and immediately replace it with a new one if any deterioration is observed. Homemade bamboo mekugi vary greatly in strength depending on fiber direction and drying level, so it is safer to purchase from a trusted sword shop or saya-shi. If the mekugi hole itself has enlarged, replacement alone will not provide a fundamental solution, and the handle will need to be remade or the mekugi hole repaired. In this case, be sure to consult a tsuka-shi or saya-shi.

Koiguchi Adhesion — Calm Responses When It Won't Withdraw or Won't Return

The koiguchi (the opening where the blade enters and exits the scabbard) becoming stuck so it cannot be withdrawn, or failing to return to the scabbard once withdrawn, is caused by sudden humidity changes, adhesion of internal uchiko, accumulation of oxidized old oil, and similar factors. The greatest danger is attempting to force the blade out, causing the spine or edge to strike the interior of the scabbard and inflict serious damage.

If adhesion is suspected, first do not force movement; instead, place it in an environment with stable room temperature and humidity for several hours to half a day. The minute swelling of the saya-ki may be relieved by humidity changes, allowing it to move naturally. If it still will not move, absolutely do not attempt to force it out yourself; bring it to a trusted sword shop or saya-shi. Experts have the technical skill to safely remove the koiguchi while understanding the internal structure. Also, frequently drawing and sheathing the sword for appreciation actually damages the lacquer and wood of the scabbard interior, so it is important to reconsider how often you draw it.

Handle Looseness — Understanding the Relationship Between Tsuka-maki and Nakago

When the entire handle is loose or you feel a subtle twisting sensation when gripping it, problems may be suspected not only with the mekugi but also with the tsuka-maki itself or the tsuka-ki (the wood beneath the same skin). The tsuka-maki naturally loosens with use, and for swords used in iaido or practice, rewrapping is necessary every few years. Internal deterioration of the tsuka-ki, peeling of the same skin, and loosening of the lower wrapping—difficult to judge by visual inspection alone—cannot be determined without opening the handle.

If the looseness is pronounced, the principle is to suspend use for safety and request inspection by a tsuka-shi. Especially when nakago rust is progressing, the nakago may move slightly within the tsuka-ki, potentially affecting the strength of the nakago itself over the long term. This is an extremely dangerous condition in iaido and test cutting and must never be taken lightly. On the other hand, if handle looseness occurs in a sword kept as a pure art object, while there is no immediate urgency, early restoration is desirable for future preservation.

Symptoms You Should Never Address Yourself — Criteria for Entrusting to a Specialist

There are certain conditions with Japanese swords that you must never address yourself but should always leave to a specialist. If red rust develops on the blade, uchiko is an abrasive containing polishing powder and cannot be used for rust removal; using it on the rust surface spreads scratches, so it must not be used. First, carefully wipe away old oil with soft wiping paper and confirm the extent and depth of the rust. If there is spotting rust or deep rust beyond superficial discoloration, always entrust it to a togishi. Absolutely avoid polishing it yourself. Improper polishing permanently damages the shape of the blade and significantly reduces its assessed value.

Conditions requiring specialist treatment by a togishi include the following.

• Spotting rust, deep rust
• Edge chips
• Deep rust on the nakago
• Deformation of the kissaki
• Warping of the curvature

Also, if traces of insect damage (fine wood dust or small holes) are visible inside the scabbard, this is a serious problem. If insect damage is progressing inside the saya-ki, the structure may become fragile without being visible, and the scabbard may suddenly crack one day. In this case, promptly consult a saya-shi and consider having the scabbard remade if necessary. Early discovery and early response is the golden rule for Japanese sword preservation. When you sense something unusual, consulting a specialist without hesitation is the most certain way to pass your sword on to the next generation.