An apparatus comprises a gear mechanism for imparting planetary motion about a central axle to a plurality of mandrels used for holding substrates in a process bath. The plurality of mandrels are mounted to a pair of end plates, the mandrels and end plates collectively comprise a carousel that rotates about the central axle. Each mandrel is also capable of selective rotation about their own mandrel axis parallel to the central axle. The substrates are held by the mandrels at their inner apertures.