Description:Matthew Boulton had to wait nearly a decade after he had built his mint at Soho to achieve his ambition of producing the national coinage. He signed a contract in March 1797 for 480 tons of 1d pieces (the famous cartwheel penny) and 20 tons of 2d pieces. It was realised, however, that the original design of the coining presses relying on a horizontally spinning cam wheel was gradually shaking apart the whole of circular framework which held the presses. A large contract would, therefore, be impossible to fulfil.
John Southern, one of Boulton’s engineers, suggested an entirely different approach, relying entirely on vacuum power rather than partly on mechanical power. This was agreed in January 1798 and from henceforth the steam engines for Boulton’s coining presses would pump a vacuum (admittedly only partial) in a long cylinder, rather than be connected directly to shafts and cogs. The latter arrangement with presses in a circle continued to be used for the cutting out of coin blanks as this job did not require as much force as stamping an impression on a coin.
Coining presses would now be disposed in a straight line parallel to the vacuum tube. The press room at Soho was abandoned and a new one built alongside. The topography of the site, possibly over the site of former menagerie pens, forced it into a curve. Building work began on the new press room in May 1798 and continued well into 1799. A 23in steam engine was installed in a new engine house leaving the earlier 16in engine in position. Boulton was very secretive about his new coining technology, but did not mind having the Russian ambassador visit in order to try to sell his first mint abroad.
By May 1799 the new press room was working satisfactorily and the national coinage was commenced. Under revised contracts the Soho Mint produced 26 tons of farthings, 526 tons of halfpennies, 1226 tons of pennies and 40 tons of twopencies by the end of 1799, a phenomenal achievement.