Pegs, wedges and shachi

In timber tsugite and shiguchi, pegs and wedges are sometimes used together with the joint to make the connection firm^[10]. For convenience this article divides them into three: pegs (komisen, daisen and hanasen), wedges (kusabi)^[17], and shachi (thin, long pegs of rectangular section)^[7]. It covers the direction in which each is driven, how it tightens, what it holds, and in which tsugite and shiguchi it is used.

Pegs: passing through to stop pulling out

A komisen is a small piece of wood driven from the side of a post to fix a nuki (a penetrating tie beam)^[16] or similar member passed through the post^[1]. According to Shimoyama, when a tenon is passed through a post and a komisen is driven from the side of the post, the peg keeps the tenon from pulling out^[3].

A peg is driven from the side of the member into which the tenon has been inserted. In the example above that member is a post. In the Naga-hozo sashikomi-sen-uchi (long tenon with a square peg) on this site, the long tenon at the foot of a post is inserted into a horizontal member such as a sill, and the komisen is driven from the side of that horizontal member, so the tenon and the peg are the reverse of the example above.

A hanasen is a method in which the tip of a tenon is pushed out beyond the post and a peg is driven along the face of the post to fix the tenon^[3]. An architectural glossary says that a komisen is driven into the post whereas a hanasen is driven into the tenon that has passed through, and that a hanasen is a slender piece of wood made to flare toward the end, often of rectangular section^[2].

A daisen is the peg used in the okkake-daisen-tsugi. The architectural glossary describes the Okkake-daisen-tsugi (sloped scarf splice with square pegs) as an okkake-tsugi with pegs driven in from the side, and says that without the pegs it is an okkake-tsugi^[8]. According to Shimoyama, the pegs are driven from the thicker side, and the two pegs are driven in different directions^[3]. The ago has a sliding slope, and the shoulders come into close contact as the joint seats^[8]. The Kanawa-tsugi (rabbeted scarf splice with a square peg) is also a splice in which the members are put together and fixed with a peg^[3][9].

On the effect of pegs, the test report of Toda says that using a komisen in a koshikake-kama-tsugi (housed gooseneck scarf joint) improved both the maximum load and the toughness^[11].

For the method of offsetting the peg holes to tighten the joint (the draw), no description was found in the sources checked.

Wedges: driven in to lock

The architectural glossary defines a kusabi as an arrow-shaped piece driven in when splitting two members apart, and says that driving it in can fix two members tightly together^[4]. In the nuki method, where a nuki is passed through a post, wedges fix the nuki^[5]. In the construction record of Kameya Komuten, there is a gap in the post hole through which the nuki passes, and wedges are driven into it to fix the nuki. The lowest wedge is driven under the nuki^[12]. The Standard Specification for Timber Construction of Public Buildings of the Ministry of Land, Infrastructure, Transport and Tourism says that the nuki is passed through the post and tightened from both sides with wedges^[14]. A paper of the Architectural Institute of Japan treats three kinds of wedge for post and nuki joints, futsu-kusabi (ordinary), naname-kusabi (slanted) and kasane-kusabi (stacked), and calls the ordinary wedge, in which wedges of the same shape are driven from left and right at the top of the nuki, the most common form^[13].

Shimoyama also describes the wari-kusabi (split wedge), in which a tenon is passed through a post and a wedge is driven into its tip, so that the tip of the tenon spreads and cannot be pulled out^[3].

If a wooden wedge is cut with the wrong grain, it splits along the grain when struck^[4].

Shachi: driven at a slant to draw together

According to Marusei Komuten, a shachi is a thin, long peg of rectangular section, made of hardwood, and generally of keyaki (zelkova)^[7]. Kobo Tsushin Yuyu says that, to splice two members, a shachi-michi (the groove for the shachi) is cut at a slant between the shear faces and a shachi-sen is driven in (the source spells shachi-michi with a variant character)^[6]. Shimoyama likewise says that the groove for the shachi-sen is cut at a slant, and that driving the peg draws the members together and presses them tight^[3].

In the sao-shachi-tsugi (long tenon splice locked with shachi), shachi-sen are driven at both ends of the sao (a long rod-shaped neck)^[18] and the mortise to tighten the joint^[7]. Marusei Komuten says that the driving can be adjusted and more driving can be added later, which makes the splice suitable where no gap is wanted at the shoulders^[7].

See them in 3D

• Pegs: Naga-hozo sashikomi-sen-uchi and Naga-hozo sashi hanasen-uchi
• Tsugite using daisen and komisen: Okkake-daisen-tsugi and Kanawa-tsugi
• Wedges: Nuki-kusabi
• Shachi: Sao-shachi-tsugi and Nihozashi sao-shachi
• All joints