I recently serviced a Brodmann BU-128 vertical from 2009, which had some of the worst bobbling I've ever seen.
I did some regulating, but this piano was especially stubborn. The jacks cleared the hammer butts with plenty of room--aftertouch was not the issue. The tops of the jacks look especially deep, so in a way I'm not surprised. It's kind of like walking through a screen door that closes quickly and nails you on the way out.
Anyone encountered one of these pianos? I've sent an email to the company describing the issue, but no response. Hence my post.
Here's a thought though: We can adjust the fore-aft position on grand jacks so that we get the fastest performance but without "cheating." Is it possible to somehow do the same with vertical jacks? Perhaps they lie at rest too deeply under the hammer butts, and if a thicker rest felt were installed, the back of the jack would clear the butt faster? Of course one would have to make sure the jack didn't cheat under a hard blow, just like a grand. What about experimenting by gluing a bit of felt on the back of the jack itself with just a small dot of glue? If it worked, would that extra mass impede the motion of the jack with too much inertia? One could of course replace all the rest felt if something of just the right thickness could be found.
If the jack were tilted a small bit forward, I suppose it would compress the spring a tiny bit more. Hopefully there would be enough adjustment in the letoff screws to compensate.
Any commentary on my thought experiment? Maybe I'm reinventing some square wheel that's already been left at the side of the road...
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Scott Cole, RPT
rvpianotuner.com
Talent, OR
(541-601-9033
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