Every once in a long while I run across one of these Wurlitzer studios. Aside from the "Uniplate" moniker you wouldn't think it any different from an average studio size vertical from this era. (1928) When you start to tune it however it feels substantially different. That's because there is no wooden pinblock. Instead the pinblock is cast iron and an integral part of the plate.
In a tight wooden pinblock when raising--or lowering--pitch you can feel the sensation of the tuning pin twisting before it jumps into a new position. I say "twisting" advisedly, because this has often been the way the phenomenon has been described to me and I have heard of though not witnessed personally an experiment to demonstrate this where a short cross piece of wire was attached the bottom of a protruding tuning pin so you could witness that it did not move in conjunction with the top of the pin.
I've always accepted this explanation but the feel of this pinblock makes me question it because the tuning pins move with very little if any of this twisting sensation. They're quite firm in the pinblock and the torque is rather high but when they move, they move. You can not pull the pin up a little and then see the pitch drop when you release it.
I always get a kick out of these oddball pianos for this reason: because it opens your eyes to things that you take for granted. To give two instances: I learned a lot about how soundboards react to changes in pitch by tuning those old Yamaha "portable" grands that had strings but no soundboard (there was a pickup for each unison) CP70s I believe they were styled. And working with Mason-Hamlin screw-stringers opens your eyes to how much of the reaction to a pitch raise is dependent on the tuning pin itself. In both these instances I had the impression that compression of the soundboard was responsible for at least 95% of the drop that resulted from a pitch raise, since in the case of the CP70s there was very little, and with the M-Hs they reacted pretty much the same as a conventional upright.
Now I'm beginning to question this demonstration of the twisting tuning pin which has been related to me on more than a few occasions but which I have never witnessed. I believe the phenomenon could be more easily explained by the wood fibers of the pinblock twisting and not the tuning pin itself. In which case the bottom of the tuning pin would not diverge from the top. Is this another of those bits of folk wisdom that get perpetuated by repetition or because people see what they're told what they've seen?