Abstract <p>Obtaining high-quality mixtures of solid dispersed polymer components in a special rotary device, as a preliminary stage of their processing before loading into a casting machine, contributes to compliance with the regulatory indicators of the 3D printing product, including color rendering, strength characteristics, etc. This process of mixing polymer media acquires particular relevance when using secondary raw materials. The formation of an engineering technique for calculating the main parameters of a rotary mixer of secondary and primary polymer dispersed materials (from the IV flowability class according to the Kerr classification) in a specified volumetric ratio is the goal of this study. The proposed method of rotary mixing of these media in crossing flows involves their separate feed using two units “mixing drum with rectangular blades–fixed relief platform” (stage 1) into the operating zone of the apparatus, in which the formed flows of heterogeneous particles are reflected from inclined baffles (stage 2). The specified blades are fixed on the surfaces of the drums in rows with angular displacements. The theoretical basis for the method of calculating the rational limits of change in the parameters of rotary mixing of polymer components is stochastic models of the studied process at stages 1 and 2 with allowance for the design features of the mixing units of the apparatus and the physical properties of the processed solid dispersed polymer components. When calculating the limiting values of the main operating parameters (angular rotation speeds of the mixing drums), a modification of the Froude criterion is adopted. In the paper, the block diagram for calculating the sought rational limits of change in a number of design parameters of the mixing drum, its blades, the relief platform for the units of the apparatus, and the corresponding inclined reflective surfaces (baffles) is described.</p>