यनतरदरवयण — Materials and Components: Wood, Leather, Cloth, Wheel and Rod

What were Bhoja's machines made of, and from what parts were they assembled? Chapter 31 of the Samarāṅgaṇasūtradhāra has no separate section on materials, but the information is spread across the chapter: an inventory of means and parts in 31.25cd–27, the vessels that hold fire in 31.36, the wooden-and-leather body of an automaton in 31.101–103, a copper whistle-tube in 31.89, water pipes in 31.119–120, a recipe for a sealing compound (vajralepa) in 31.130–132, and an iron pivot and pin-wheels in the revolving pavilions of 31.177 and 31.209–210. This article collects these passages. Read together they describe a coherent material practice: light wood for frames and figures, joined with pegs and covered with leather; cords pulled and released over wheels for motion; metal (copper, iron, tin, wire) for tubes, vessels, pins and bearings; cloth and leather for bags and membranes; and an organic sealant of lac, resin, horn powder and oils for watertight joints. The components named — wheel, rod or shaft, spindle, pin, cord, pipe, bag — are the elementary machine parts of any pre-industrial tradition. The article identifies each, maps it to its modern counterpart, and marks the readings that remain uncertain in the printed text. Article 4 of the series Yantravidhāna Studies (SSD-31), on chapter 31 of Bhoja's Samarāṅgaṇasūtradhāra. Verses discussed: 31.25–28, 31.36, 31.101–103, 31.130–132. Web version: sanskritmanthan.in/a/ssd-31-04-yantra-dravya