ring 13 the ball bearing 11 supports a bearing block 10 secured with an outer spring ring 12 the upper vacuum disc 17 is inserted and secured in the lower edge of the bearing block 10 for example with a suitable adhesive for observing the bonding operation of the two dvd halves 23 and 24 and to optimize the process based on the results the upper vacuum disc is made of glass while the support bracket 19 and the bearing housing 9 are provided with openings 48 through which the glass vacuum disc 17 and the processes occurring underneath the vacuum disc can be observed an annular member 49 having a vacuum channel connected to the vacuum channel 55 in the upper vacuum disc 17 as well as to the vacuum channel 50 extending through the bearing housing 9 and the support bracket 19 is glued to the upper vacuum disc 17 two glass discs with one of the glass discs provided with a groove can be glued together to provide the vacuum channel 55 in the glass vacuum disc 17 an annular groove 57 can extend on one of the opposing surfaces at the interface between the annular member 49 and the bearing housing 9 to maintain the vacuum during rotation sealing elements 65 and 66 are provided above and below the annular groove 57 to maintain the vacuum the vacuum channel 50 is connected to a vacuum pump in a known manner an upper centering pin 40 extends from above through the support bracket 19 the bearing housing 9 the annular member 39 and the central opening 60 in the upper vacuum disc 17 and continues into the space between the two dvd halves 23 and 24 the vertical position of the centering pin 40 can be.