The results of laboratory studies confirming the possibility of preliminary separation of free grain from the stripped grain heap before it enters the threshing chamber of a combine harvester are presented. For example, it has been established that the maximum free grain passage through the holes of the lath bottom is 68, 7% with a width of its holes of 8 mm and a length of 160 mm. The length increase of the lath bottom of the inclined chamber of the combine harvester up to 1182 mm ensures a complete separation of grain from the heap and exclude the possibility of its falling into the threshing chamber.

The article presents the results of laboratory studies, confirming the possibility of preliminary separation of free grain from the hatchelled grain heap before it enters the combine harvester threshing chamber. It has been established that the most promising methods for performing this technological process are a mesh conveyor mounted in front of the thresher and an inclined chamber equipped with a grating bottom with oblong holes. The experimental results indicate that the maximum passage of free grain through the openings of the mesh conveyor 2000 mm long is 94.66%, and for an inclined chamber with a grating bottom 950 mm long – 68.7%. To ensure the passage of 99% free grain, the length of the mesh conveyor separating surface should be at least 2.69 m, and the length of the inclined chamber should be 1.17 m. The practical implementation of the first separation method requires shifting the threshing drum back and drastically shortening the straw walker. The second method of separation is more acceptable, since it does not require a substantial rearrangement of the serial harvester.