Roberts built a range of machine tools, some to his own design, the first being a gear-cutting machine. For accurately checking the dimensions of the gears he adapted the sector, which he developed for sale to other engineers. Roberts adopted rotary cutters, which he had seen used at Maudslays. This is one of the earliest records of a milling cutter used in engineering. In 1816 he made the first reliable wet gas meter. In 1817 he made a lathe able to turn work . This had a back gear to give an increased range of speeds, and a sliding saddle to move the tool along the work. The saddle was driven by a screw through gearing which could be disengaged when the end of the cut was reached. Also in 1817 he built a planing machine to allow the machining of flat surfaces. Previous to this flat surfaces were laboriously made by hand with the fitter using hammers and chisels, files and scrapers to get a true surface.