Development of the modern communication systems necessitates the creation of mirror reflectors for antennas made of polymer composite materials. It allows to significantly reduce the weight of reflectors making them more precise and dimensionally stable. However, the actual process of manufacturing of the composite reflectors is often associated with distortions of their reflecting surface occurring because of process-induced deformations. The analytical dependences have been obtained that allowed predicting the regulated tolerance band for assembly by gluing or connection with screws of the composite products with frames such as parabolic antenna reflectors. These dependences take into account the product design and assembly process parameters, as well as strength characteristics of the adhesive, the rational combination of which allows achieving a high quality of the reflector. As shown by the example, recording of spring action depending on the unbalance of internal forces of the assembled product does not make a substantial correction to the tolerance for the theoretical contour of the mirror antenna reflector at the actual design parameters of its elements. Tolerance bands for gluing and connecting with screws are compared. It is proved that the frame to reflector connection with screws can be more effective at their rational number, but when this number is fairly large, the realizable tolerance band is almost the same. Our findings allow solving the new process tasks in order to determine the maximum permissible deviations of composite shells from their theoretical contour at the assembly stage.