[pianotech] Pinbloc/plate flange gap

[Ron Nossaman]

On 1/13/2011 3:38 PM, Claude M. Harding wrote:
> A church near me has a small grand (Yamaha GA1) that doesn't stay in
> tune very long. The temperature is kept between 60 & 80, and the piano
> has a
>
> Dampp-Chaser heat bar and humidistat.

But no humidification tank, right? It's Winter, right? The heat's on, 
right? There's no humidification system in the building, right? It's a 
GA1, right? The temperature is *KEPT* between 60° and 80°?!!! How is 
that conducive to tuning stability? All you local tuners record RH% 
readings on a card in the piano with each tuning, right? Not 
temperature, relative humidity, so you have a baseline of useful data 
against which to correlate tuning drift. How long is the "not very long" 
that the piano stays in tune, and what are the RH% readings at the last 
half dozen tunings?

Case in point; I tuned five at one of my colleges today. Six months ago, 
the pianos were tuned at 70° and 76%RH. Today, they were at 70° and 
18%RH. The temperature range is very closely controlled, and we're 
talking 30¢ pitch change through about half of the piano twice a year. 
I'll be doing five more tomorrow, at 70° and more likely about 22%RH 
(it'll be warmer outside), and they'll all be 30¢ low in the middle and 
up into the treble.


> Two other competent tuners have also tried to tame this little beast
> without much success. The last time I tuned it (Aug. '10) I pulled the
> action and checked the
>
> mating of the pinblock and plate flange. I used my 6-in. metal ruler
> (.018" thickness) and found gaps between the pinblock and plate flange
> from F#3 to A#4 and also
>
> from B6 to A#7. The plate flange ended at A#7, so I guess the top "gap"
> runs from B6 to the treble inner rim where the pinblock is fastened.
>
> How likely is it that this is the source of the instability.

I'd think not remotely. I'd be very surprised if filling the gaps 
resulted in any improvement at all.


>If so, do
> you have any suggestions for improving the situation, short of a
> rebuild, which is not likely to happen.

A rebuild won't help it either, unless you can change some basic design 
problems. These are wretchedly scaled little cheese slicers, that can't 
even be realistically tuned at all, much less kept stable. Your only 
hope is a *full* Dampp-Chaser system, and a long cover. A bottom cover 
would help too.

Luck,
Ron N