Hi Dover:
I agree that a not-so-clearly-defined contact between spindle and clamp (neither snug nor free) is not a good idea. One some turntables, you'd want physical contact between the clamp and spindle, as this is what would allow the clamp to terminate the noise and vibration of the platter bearing. Something like a collet-chuck mechanism should do the job well. However, the FAR's self-lubricating polymer thrust plate is pretty quiet as far as I recall, and shouldn't need special treatment.
A slight overbore of the clamp combined with a polymer sleeve should be good. But not with teflon. Teflon is soft and has low elasticity, and once it is deformed, it stays that way. If you apply pressure across a wide area of teflon it stands up pretty well, but concentrated pressure on a small area is another story. Delrin or some grades of modified noryl (PPO) should be better.
You may also try a tripod-contact between the bottom of the clamp and the LP surface. For whatever reason, I thought that this worked pretty well on the FAR.
Regarding your second question, with the s-l-o-w spin-up time and all, would you really want a peripheral clamp on your FAR? (grin) Sounds damn fine without one!
I haven't had a problems with graphite mats, by Audio Tekne, A.R.T. and Boston. However, I have fabricated some parts in graphite, and I know that there can be sizable differences in the materials sourced from different suppliers. Some lend themselves to machining, and others don't. Also, for best results, graphite machining should be done by a place that is familiar with the stuff, IME.
As an aside (Dover, you already know this), in Kitamura's original FAR design, the platter was aluminum, and it was topped with a mat of machined chrome-copper. Either piece would ring beautifully on its own (although you'd not see it in the measured frequency response from the cartridge), but place the mat on the platter, and pfft! No more ringing, and a quieter, more even-handed sound delivery with greater dynamic range (although you't still not see anything on the cartridge's measured frequency response). The Japanese phrase for this type of mechanism would translate to "phase-interference damping". No idea what you'd say in English.
FWIW, I'm using the same principle in some of my cartridge designs (pressure-fitting of dissimilar metals which are chosen to suppress each other's resonant tendancies).
cheers, jonathan carr
PS. On paper, at least, another approach would be to get a snug fit between the clamp and spindle, and put a stiff grease on the spindle. The grease would lock the clamp in place and quash any ringing. You'd have to remember to wipe the spindle clean each time before removing the LP, however!
Yet another approach that you can take with clamps is to use a container filled with small ball-bearings. Staggering the bearing sizes helps to expand the range of affected frequencies.
