Leach and Keith suffered a failure in the winter of 1842 owing Mason a large amount of money. James K. Mills & Co. of Boston, a leading commission firm, came to his rescue and helped him to buy out the former partners. In 1845, new buildings were erected and the plant became the largest one devoted to the manufacture of machinery in the country. It made cotton machinery, woolen machinery, machinists' tools, blowers, cupola furnaces, gearing, shafting, railroad car wheels made with spokes, and after 1852, locomotives.