to fix the adjustment plate 102 on the support plate 33 in addition to supporting the bearing means the bearing mounting plate 110 is adjustably tiltable by means of the adjustment screw 113 which depends from the seal mounting plate 110 into bearing engagement with the upper surface of the adjustment plate 102 from the above it will be seen that the adjustment plate 102 and the bearing mounting plate 110 are independently adjustable and cooperatively interact to provide the properly aligned coaxial and vertical relationships of the bearing 80 and the driveshaft assembly 50 a coupling plate 114 is positioned atop the bearing mounting plate 110 and is free to float into aligning relationship with the bearing mounting plate 110 and the depending tubular shaft 24 and or 28 of the reaction chambers 22 and 26 respectively once the aligned relationship has been established such as during initial assembly of the substrate supporting mechanism 20 the coupling plate 114 may be tightened down against any further additional movement such as by means of the illustrated bolt 116 and others not shown the coupling plate 114 is formed with an axially upwardly extending externally threaded boss 118 and an axial core 120 is formed through the coupling plate an o ring seal 122 is provided at the upper end of the boss 118 so as to be in sealed circumscribing engagement with the peripheral surface of the depending tubular shaft 24 or 28 a clamping nut 124 having an axially opening 125 formed therethrough is threadingly carried on the boss 118 to exert a circumferentially compressive force on the o ring seal 122 by.