The paper presents the results of the screening process by rotation of a conical sieve. It is a machine sieve, wherein the sieve has the shape of a cone and is rotating around a vertical axis or slightly inclined from the vertical. The layer of granular material fed to the sieve takes the complex movement of the spiral – both in the radial and circumferential cone sieve. It is then subjected to a changing centrifugal force, moving along the varying radius of the cone sieve. This type of movement of granular layer allows to achieve good processing results of the screening machine. Machines of this type should be used for screening materials, fine and very fine grained. Such materials are difficult to classify in a typical, commonly used screening machines. The design of the test screening was developed by the authors of this article and then registered in the Patent Office in the form of two patents.