Model of patent reaping machine, 1870, scale 1:8

The first major improvement to the type of the reaper established by McCormick and Hussey, was the addition in 1851 of mechanically rotated rakes or sails. These were driven by the main wheels as the reaper moved forward and were usually of two kinds. The plain boards pressed the crop against the knives for cutting, the actual movement being controlled by the arms which had to follow the contour of a special guide ring. A separate guide ring giving a different movement caused the other boards or rakes to sweep the crop collected on the deck into sheaves, and deposit these in rows at the side of the machine.