the undercaridge is the fiddley bit, there ia also 2 little doors that are held in with a wire spring, dont use this as the undercaridge wont go on, glue the little doors on last .
its the old addage metal and plastic some times dont go together
because you can wind the undercaridge up or down with key, i chose to have this solid as its very flimsmy, so when you build the bay glue the moving parts for a solid undercaridge
Mike