@slaw
I use a custom spindle for the air bushing (thrust and radial air bearing), which supports a cast iron platter and the graphite mat on a machined stainless taper. Part of the design is an extension of appropriate length to serve as a record-centering spindle. I daresay an extension could be made to accommodate any TT for a few hundred - but it does need precision machining.
The reason for a two-piece spindle is simply experimental uncertainty - I didn't know what would work. By itself the cast iron rang, by itself the graphite rang, but together on the spindle they are as physically dead as Archimedes.
I use a custom spindle for the air bushing (thrust and radial air bearing), which supports a cast iron platter and the graphite mat on a machined stainless taper. Part of the design is an extension of appropriate length to serve as a record-centering spindle. I daresay an extension could be made to accommodate any TT for a few hundred - but it does need precision machining.
The reason for a two-piece spindle is simply experimental uncertainty - I didn't know what would work. By itself the cast iron rang, by itself the graphite rang, but together on the spindle they are as physically dead as Archimedes.