 New iron casting techniques pioneered by the Coalbrookdale Company in the 1720s allowed bigger cylinders to be used, up to about 6 feet (1.8 m) in diameter by the 1760s.Experience led to better construction and minor refinements in layout.Its mechanical details were much improved by John Smeaton, who built many large engines of this type in the early 1770s; his improvements were rapidly adopted.