Why were early steam-engine cylinders difficult to bore accurately?

Early steam-engine cylinders were difficult to bore accurately because existing methods lacked the necessary precision to create perfectly cylindrical internal surfaces. Before the development of specialized machinery, the tools used for boring were often unstable, leading to irregularities that prevented a tight fit between the piston and the cylinder wall.

This challenge was largely overcome in 1775 when the British ironmaster John Wilkinson invented a new boring machine. By providing a more stable and precise method for boring engine cylinders and cannon barrels from solid castings, Wilkinson’s innovation enabled James Watt to perfect his steam engine, as it ensured the cylinders were sufficiently accurate to maintain the pressure required for efficient operation.1