According to the results of laboratory experiments, the optimal angle of inclination of the holes of the lattice bottom of the inclined chamber of the combine harvester is established, which provides maximum separation of free grain from the combed grain heap before it enters the grind chamber. This allows you to minimize the intake of free grain to the threshing device, securely eliminating the probability of crushing the working bodies grind. Studies were carried out on wheat varieties «Moscow 56». The grain moisture content was about 12%. The speed of the conveyor 3 m/s and the angle of inclination to the horizon of 45° correspond to similar parameters for most modern combine harvesters. The angle of inclination of the lattice bottom opening had seven levels of variation within 0-90°. The feed of the combed grain heap was about 10 kg/s with a content of 80 % free grain. The length of the removable grating bottom was 0.95 m, and its rectangular holes had a size of 160×8 mm. To eliminate the effect on the output parameter, the area of the «live section» of the holes of the lattice bottom in all series of the experiment was taken the same. Thus, results of scientific researches, increasing of the angle of inclination amounts of free grain passed through the holes of the bottom lattice is reduced, and the number came down from his grain, on the contrary, increases. The maximum separation of free grain 68,7 % corresponds to the angle of inclination of the holes equal to 0°. To ensure complete separation of free grain from the combed grain heap, the length of the separating surface must be at least 1,18 m. This technical solution can be implemented, for example, in the inclined chamber of the grain harvester KZS-1218 «Polissya GS-12», which has a length of about 1,3 m.

The results of the laboratory experiment confirming the possibility of preliminary separation of free grain from the combed grain heap before it enters the threshing chamber are presented. In particular, it is proposed to provide a combine harvester with a device for pre-separation of free grain, mounted between the inclined chamber and the threshing device. It includes two drums and an infinite mesh cloth. To intensify the process of separation of the combed grain heap on the fraction of the axis of rotation of the drums are made eccentrically with respect to their geometric axes. All studies were carried out on wheat varieties «Moskovskaya 56». Grain moisture was about 12 %. The speed of movement of the floating conveyor had five levels of variation in the range of 3-5 m/s. Flow oceanog grain heap was about 10 kg/s at a content of 80 % of free grain. The length of the mesh conveyor was 2 m, and its rectangular cells had dimensions of 17×15 mm. Thus, according to the results of scientific research, as the speed of the mesh conveyor increases, the amount of free grain passing through its cells tends to decrease, and the amount of grain coming down from it, on the contrary, to increase. The maximum passage of free grain (94,66 %) corresponds to the minimum speed of the mesh conveyor, equal to 3 m/s. The presence of free grain is due to the fact that during a series of experiments, the length of the separating surface was insufficient. To determine the optimal length of the mesh conveyor, the nature of the process of preliminary separation of free grain from the combed grain heap is considered. Extrapolation of this process shows that the minimum length of the mesh conveyor, providing 99 % of the free grain from the combed grain heap, must be at least 2,69 m. The practical implementation of such a technical solution in the design of a modern combine harvester will increase its productivity when combing plants at the root, reliably eliminating the possibility of crushing free grain by the working bodies of the threshing device.