Design of cutoff bar

[Delwin D Fandrich]

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  ----- Original Message -----=20
  From: BobDavis88@aol.com=20
  To: pianotech@ptg.org=20
  Sent: May 08, 2003 8:27 AM
  Subject: Design of cutoff bar


  Many pianos with cutoff bars have an open space, or a different =
species of [filler] wood outside the cutoff. Is there a way to gain the =
acoustical advantage of a cutoff bar, but have it appear traditional on =
the top side? For instance, could the ribs be notched and continued on =
to the rim, just to support this area? I realize this is a waste of good =
spruce, but it would not call attention to itself, and there are some =
situations in which that is a good thing.
Yes. In some cases we leave the soundboard full-size and glue it down =
over the cutoff. We still terminate the ribs at the cutoff and use short =
pseudo-ribs between the cutoff and the rim to support the dead area of =
the soundboard. It is much more difficult to glue up this way and we =
resist doing it unless the client is really insistent. Generally we glue =
up in two stages. The soundboard board goes in first so we have ready =
access to the cutoff for clamping. Then the filler goes in. Clamping is =
not a critical. We always put something in there to keep acoustical =
energy from cross-coupling around the edge of the cutoff.

  Is the cutoff bar affixed to the beams? In one picture it appears to =
pass over the metal termination plate for the beams. Is this a problem?
Yes. It is glued and doweled. In general we cut away for clearance =
between the cutoff and any metal components (Usually incorrectly called =
"tone-collectors") that may be down there. This includes any =
"Centripital Tension Resonators" that may be in the way.



It appears to be the approximate cross section of a bridge. Am I seeing =
this right?

No. They are some larger that that. I usually make them 50 to 60 mm wide =
and between 30 and 50 mm tall. They are made of maple (usually).

Del


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