Hamachi and Munemachi Finishing Techniques: The Precision Grinding and Hammering That Defines the Blade-Tang Boundary After Quenching

What Are Hamachi and Munemaichi?

At the boundary between the blade and the nakago of a Japanese sword is a notch called the "machi." The notch on the blade side is called the "hamachi," and the notch on the spine side is called the "munemaichi." This machi is a functionally and aesthetically crucial part, serving as the reference point where the habaki is fit precisely. The manufacturing techniques of the habaki itself are detailed in The Work of the Shiroganeshi.

The shape of the machi varies subtly depending on the swordsmith's school and era, and also serves as an aid in determining both the period and maker in authentication. The craftsman's individuality appears in the details: shallow and sharp machi, rounded machi, and the amount of machi-okuri.

The machi is also used as a reference point for measuring the dimensions of various parts of the blade. If the position of the machi shifts, it affects the very measurement of the distance from there to the kissaki, so the precision of the machi is an essential element in dimensional management.

Problems Arising After Quenching

In Japanese sword making, quenching (yaki-ire) is the most nerve-wracking process. By rapidly cooling the steel through water quenching (mizu-yaki) or oil quenching (abura-yaki), the hamon is formed and the blade is given hardness. However, various deformations occur in the blade during this rapid cooling process.

• Changes in Curvature: The curvature (sori) of the blade changes before and after quenching. While the swordsmith anticipates the calculated change in curvature in advance when preparing the clay coating, it is not something that can be completely predicted, and fine adjustments are often necessary after quenching.
• Twisting (Nejire): The blade may twist slightly. For small twists, correction is made while the blade is still hot.
• Deformation Around the Machi: The area around the machi, which is the boundary between the blade and the nakago, is prone to fine deformation due to the rapid temperature difference during quenching.

If the machi becomes deformed, it affects the fit of the habaki. If the habaki does not fit properly, the blade becomes loose within the scabbard, and can even damage the blade itself.

The Finishing Process for the Machi

The finishing of the machi after quenching may be done directly by the swordsmith or by a polisher. Let me explain the typical process.

Rough Correction (Ara-shuusei): Immediately after quenching, while the blade still retains heat, rough deformations are corrected by light tapping with a hammer (tsuchi). This process must be completed in a very short time, testing the swordsmith's judgment and experience.

Shaping the Machi: Using a rod whetstone (bo-toishi) or specialized small whetstones, the notch shapes of the hamachi and munemaichi are refined. The depth, width, and angle of the machi are precisely managed to match the habaki's dimensions. Excess metal is removed with a chisel-like tool and finished with whetstones.

Fitting Adjustment with the Habaki: The habaki made by the shiroganeshi is provisionally fitted, and the fit with the machi shape is confirmed. If gaps appear, the machi is filed down; if the fit is too tight, fine adjustments are repeated. Mutual adjustment between the machi and habaki continues until they are perfectly flush.

Final Finishing Polish: The area around the machi is finished with fine whetstones. In "sashikomi-togi" (push-in polishing) performed by a polisher, the blade's rise from the machi to the edge is refined, and the hamon is polished to appear clearly right up to the machi.

The Temporal Character Shown by Machi Shape

The shapes of the hamachi and munemaichi have characteristic tendencies for each era. They are one of the important clues in authentication.

• Kamakura Period: The machi notches are clear and sharp-angled. The boundary line with the blade is beautifully and orderly.
• Muromachi Period: The shape of the machi diversifies, and particularly in mass-produced swords tends to be simplified.
• Edo Period (Shinto/Shinshinto Period): There is a tendency to consciously treat the machi as a design element, with the school's characteristics appearing in the machi's angle and depth.

Furthermore, "machi-okuri" (the machi being displaced from its original position when the blade is shortened by "suri-age") is important evidence indicating later restoration. In swords where machi-okuri has been performed, the number and arrangement of the mekugi-ana (peg holes) remaining on the nakago may show irregularities, and the authenticator infers the sword's original condition by looking at these traces comprehensively.

Perspectives for Observing the Machi's Condition

When appreciating a sword in hand, the machi is often overlooked, but observing it from several perspectives can provide clues for reading the sword's condition and history.

• Bilateral Symmetry: Check whether the angle and depth of the hamachi and munemaichi are aligned. If there are extreme distortions, the sword may have been affected by wear from long-term polishing or past repairs.
• Fit with the Habaki: Examine the machi with the habaki removed, checking for wear or gaps. If the fit is loose, the habaki may have been replaced with a later supplementary one different from the original.
• Luster Around the Machi: The area just above the machi receives the finest finish polishing, and the clarity of the hamon serves as a basis for judging the entire sword's polishing condition.

These observations do not replace expert authentication, but are useful perspectives for developing the habit of viewing swords carefully.

Points to Be Careful About in Maintenance After Ownership

The area around the machi, like the blade's edge, requires careful handling.

• Do Not Touch Bare-Handed: For the same reason as not touching the edge directly, skin oils around the machi become a source of rust. When maintaining it, use uchiko powder or a soft cloth.
• Check How It Fits Into the Scabbard: If the fit between the habaki and the machi is misaligned and you force the blade into the scabbard, it can damage the interior of the scabbard or the machi itself. If you feel resistance, do not force it—check the habaki's position again.
• Regular Inspection: By developing the habit of checking the area around the machi during each maintenance session for signs of rust or discoloration, you can easily notice abnormalities early.

Modern Swordsmiths Speak on the Finishing of the Machi

For modern swordsmiths too, finishing the machi is one of the nerve-wracking processes. Using whetstones and precision files, they work to 0.1mm accuracy and repeatedly achieve a precise fit with the habaki made by the shiroganeshi.

This process is handwork dependent on the craftsman's sense and experience, something that cannot be replicated by computer-controlled machining. Among swordsmiths, some finish the machi themselves all the way through, while others divide the work with a polisher—the methods vary—but it is commonly understood that the quality of the machi finishing significantly affects the overall completion of the sword.

Summary

The finishing techniques for the hamachi and munemaichi occupy an unassuming yet crucial position in Japanese sword manufacturing. By understanding this process—from correcting deformations after quenching to achieving a precise fit with the habaki—in which the craftsman's skill and experience are concentrated, one can more deeply appreciate the profundity of Japanese sword as a craft.

The machi not only conveys the craftsman's skill at the time of creation but also serves as a clue for reading the sword's history and condition, making it a part worthy of attention in both appreciation and maintenance.