A backing plate unit for a rotary grinding machine includes a backing plate with a front face for mounting a grinding disc and a back face opposite the front face, a drive shaft that can be attached to the tool adaptor of the rotary grinding machine, and a suction hood that is rotatably fixed to the drive shaft. The backing plate 10 includes suction openings that penetrate the backing plate so that the suction hood 30 vacuums dust through the backing plate to the back face of the backing plate.