One method used for some purposes was to coil two wires around a core in close contact with each other. One of these was then removed, leaving a space corresponding to the hollow of the thread. The core and remaining wire were then dipped in melted tin and soldered together. In some cases they were actually used in this form as the desired screw thread. In others, the helical wire was used to guide a sleeve nut which controlled a tool used to cut a thread located farther up on the length of the core. Another method resorted to was that of grooving a smooth cylinder by a sharp-edged cutter standing at the required pitch angle and relying on the contact of the knife-edge to produce the proper traverse along the cylinder as it was rotated, thus developing the screw. This method is not so crude as it seems and was one of those used by Maudslay himself. He also used a flat steel tape wound about a cylindrical bar, but he found the inclined knife method more satisfactory. The device which he used was a mechanism of considerable refinement. He employed cylinders of wood, tin, brass and other soft metals accurately mounted to revolve between centers. The hardened knife was crescent-shaped, nearly fitting the cylinder, and fixed at the required angle with great precision by means of a large graduated wheel and tangent screw. A chasing tool carried by a small, adjustable slide cut the thread as the stock moved forward under the incisive action of the inclined knife edge. Hundreds of screws, both right and left, were made by this device, and their agreement with each other is said to have been remarkable. This was the way in which Maudslay generated his first lead screws. With the best of the screws so obtained Maudslay made the first screw-cutting lathe a few years prior to 1800, shown in Fig. 15,[37] which had two triangular bars for a bed, and was about three feet long. The headstock carried a live spindle, which was connected with a lead screw by a pair of gears, and a slide-rest ran upon the triangular bars under control of a lead screw having four square threads per inch. In this machine he at first used different lead screws for different pitches. The inner end of the lower spindle in the headstock had a two-jawed driving device, which might be disconnected and into which various lead screws might be fitted. Later he added change gear wheels. [37] No. 1601 in South Kensington Museum, London. Cat. M. E. Collection, Part II, p. 266.