Treatise on Armament Technology, Volume 85

Page 7

The crossbow stock original: nushen (弩身); the wooden body or tiller of the crossbow has a total length of 1 foot, 6 inches, and 3 fen A fen (分) is a traditional unit roughly equal to 0.1 inches or 3.2mm. Within this total length:

• The head measures 3 inches and 3 fen.
• The draw length original: guakou (掛口); literally "hanging mouth," referring to the distance the string is pulled back is 7 inches.
• The distance from the trigger hook to the tail hook is 3 inches.
• The distance from the hook to the very end of the tail is 3 inches.

The width of the head is 1 inch and 7 fen. At the bow-socket original: danyan (擔眼); literally "carrying eye," the rectangular hole where the bow-lathe or "prod" is inserted, the width is 2 inches. The section where the trigger mechanism is installed is 1 inch and 5 fen wide. At the tail hook, the width is 1 inch and 9 fen. The finished timber should have a thickness of 9 fen or 8 fen; it should absolutely not be any thinner, as one fears it would not be sturdy enough.

The magnitude of the crossbow's draw weight depends entirely on the width of the bow-socket and the thickness of the bamboo used for the bow-lathe. This specific design uses a 7-inch draw length as the standard. According to the rule of a 1-inch draw length governing 3.4 inches of the bow-lathe socket: the upper opening of the socket has a horizontal width of 1 inch and 1 fen, the lower opening is 9 fen wide, and the length is 2 inches and 9 fen. If you follow this formula, the draw weight will reach between 240 and 250 units of force original: xun (勛); likely a technical variant for jun (鈞), a unit of weight measurement used here to indicate the tension or "poundage" of the weapon.

The arrow groove original: jiancao (箭槽) ends at a distance of 1 inch and 4 fen from the trigger hook; this flat area is called the field plate original: tianpan (田盤); the flat, stable surface of the stock where the bolt rests before the groove begins. On the upper surface of the crossbow head, further out...