Bore lengths

[Overs Pianos]

>Hi folks..
>
>just got through double checking a measurement for bore lengths on a 
>Petrof grand and noticed a rather large discrepancy between on bench 
>measurements and in piano measurements


As you will with almost any factory instrument you care to measure.

>... and ended up with the following observation resulting in the 
>accompanying question.
>
>Measuring the distance between strings and keybed, then hammer 
>centers and keybed yeilded a near 2 mm difference when done on the 
>bench visa vi done in the piano. At first I thought that well..... 
>its a bit clumsy to measure in the piano.... so....  But then I got 
>to thinking about bedding issues and decided to double check very 
>closely in the piano and came up with very close to the same 
>results.  Obviously in this particular example, the bedding screws 
>accounted for a quite significant difference in the height of 
>hammer centers. This of course is directly reflected in the bore 
>length one decides on, so its kind of important to get the darned 
>thing right.

The bedding screw adjustment won't make a huge difference to the figures.

Many OEM installed hammer sets will exhibit considerable variation to 
the figures you might arrive at by measuring the keybed to string 
distance, minus and keybed to hammer centre distance, minus any 
over-centering which you might decide to include.

Most factories arrive at their respective boring lengths by taking 
them from the design drawings. Since the plate height can vary some 
from piano to piano, the string heights also will vary. This is the 
primary reason why many factory hammer-set boring regimes don't match 
the real-world piano. We bore our hammers to suit the individual 
piano by measuring the final string heights after the plate is 
installed strung and chipped. In theory, even the soundboard sinkeage 
under the downbearing force will reduce the required boring distance.

When re-hammering, its always better to measure the string heights in 
the piano, and not copy the original boring distances. But as always, 
its best to do a couple of samples and regulate them before 
committing to a boring regime for the entire set.

Seasons Greetings to all,
Ron O.
-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
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Web http://overspianos.com.au
mailto:info@overspianos.com.au
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