The corian is an adapter made so that the lamp rod screws into the one end. That end of the adapter has a small tenon in it to fit into the handwheel to just keep it centered.
On the other end of the corian there is a rabbit for the 2 stacked bearings to go into, and I uses JB weld to seal them in place. Then the air hose coupling is JB welded into the bearings.
Around the end of the lamp rod coming out the headstock is a rubber seal, actually the rubber gasket from a toilet supply line. Then that gets the washer and nut to hold the rod tight into the shaft of the headstock.
The vacuum goes from the air chuck, thru the bearing centers, a little corian, then into the lamp rod that comes out past the headstock. The rubber seal is to keep from losing vacuum from the end of the lamp rod back around the end of the lamp rod and back out the headstock hole that the lamp rod shaft is in.
So the vacuum is in the airline coming in and the to the vacuum chuck screwed onto the headstock, where you are creating the vacuum.