In 1870, Lukens constructed a new rolling mill powered by a steam boiler to drive larger rolls measuring 25 inches in diameter and 84 inches in length, and converted the old mill to a pudding mill to prepare stock for the new operation. In 1890, the firm added another mill with three rolls 34 inches in diameter and 120 inches in length between mill stands, and its 3-high configuration allowed material to pass through the mill in both directions. Believed at the time to have been the largest mill in the United States, it was driven by a large Corliss steam engine and equipped with cooling tables, hydraulic lifting equipment, and transfer apparatus to move plates easily to shearing areas. When used as a finishing mill, it facilitated the rolling of steel, which Lukens had begun to roll about 1881 and which was rapidly replacing iron for most industrial purposes. Another technological development that became a company specialty was the manufacture of heads, or bowl-like shapes, by hot spinning. As a leading supplier of boiler plate, Lukens saw a new market in supplying builders of steam boilers, tanks, and pressure vessels with formed heads for end closures as well. Before spinning machines were invented, heads were formed by hammering or "bumping" hot plates with heavy mauls, either over a stationary form or in a forming pit dug into the ground, a long and laborious process that often required several reheatings of the plate. During a visit to St. Louis in 1883, Dr. Huston and his son saw an early spinning machine in operation and ordered one for Lukens, and the company's first spinning machine began operating in 1885 as a belt-driven machine that could produce heads up to 7 feet in outside diameter and up to 1 inch thick.