Wubei Zhi (Vol. 34)

...use light saw marks as indicators. Refer to these marks when you begin the assembly. If the root and tip ends the bottom and top ends of the bamboo stalk are mismatched or reversed, it will result in the defect of one side being too soft while the other is too rigid, causing an uneven draw.

Next, use bricks or stones to prop up both ends of the bamboo stave. In the center, burn rice straw to smoke and heat the wood. This process removes the natural oils from the bamboo skin original: Zhuqing (竹青); literally "bamboo green," the hard outer dermal layer of the bamboo culm.

Heat the bamboo until the color turns a golden yellow. Once you see a small amount of bamboo sap original: Zhuli (竹瀝); the liquid essence or "tears" of the bamboo released through heating slightly seeping from the two ends, you must stop immediately. If the fire is too intense and the color becomes a scorched or charred yellow, the bamboo will become brittle, break easily, and be useless.

Alternatively, if you do not use the smoking method, you may soak the bamboo in lime water for seven days and then sun-dry it; this will prevent insects from eating the wood. This method is also effective. However, as the common saying goes: "Once the oil is removed from Miao bamboo, its strength is as great as an ox." Therefore, the smoking method is still considered superior.

When selecting the bamboo, use only those stalks that grew on sun-facing slopes. Do not use bamboo grown in the shade bamboo grown in the sun is generally denser and has better structural integrity than those grown in damp, shaded areas.

On the Dimensions of the Crossbow Stave

The length of a single stave should be two feet, three inches, and eight-tenths approximately 75–76 centimeters based on Ming dynasty measurements. The width and thickness of the center section must correspond to the stave-socket the hole in the crossbow stock of the crossbow body...