A good katana manufacturer makes sure each sword fits securely in its saya. Despite their best efforts, sometimes a sword will be loose in its sheath or become loose over time with repeated drawings,
Shimming a saya is the prefered method for tightening a katana, wakizashi or tanto in its sheath.
You will need:
- wood veneer edging
- narrow flathead screwdriver
- your sword
Step 1: Familiarize Yourself With the Saya
Start by drawing the sword and setting the blade aside in a safe place. If you look into the mouth of the saya, you will see that the width of the opening tapers. The mune (rear) side of the blade is wider and the ha (edge) side of the blade is narrow. The shim will be applied to the ha (edge) side of the saya.
There is no need to shim the entire length of the scabbard. The blade doesn't actually contact the inside of the sheath. The only point of contact should be between the habaki (the metal collar at the base of the blade) and the saya.
Step 2: Cut the Wood Veneer Shim
Use a pair of sharp scissors or a knife to cut a piece of the wood veneer edging. The strip should be as long as the habaki and as wide as the ha (edge) side of the saya opening.
Step 3: Attach the Shim to the Saya
The wood veneer edging has a heat activated adhesive on the back. Insert the shim just inside the mouth of the saya on the ha (edge) side. Heat a narrow flathead screwdriver using a lighter, candle or other heat source. It doesn't have to be red hot - it should be around as hot as a clothing iron. Once the screwdriver has been heated, use it to apply pressure to the wood shim. After 10 seconds or so, remove the screwdriver and return the sword to its saya. Putting the blade back in the sheath is the best way to get even pressure on the shim while the adhesive sets.
Step 4: Job Complete!
After the adhesive has set, you can test the fit of the sword. It should be held firmly in place but not be difficult to draw. If it is a little too tight, it will loosen naturally over time. Avoid sanding or filing the inside of the sheath as residue could end up scratching the blade.
Traditionally, shims were fashioned of the same wood as the saya and attached with a rice paste. The wood veneer edging and its adhesive are usually soft enough to avoid damaging the blade.
This tanto was loose but now can be held upside down with no chance of slipping.