request advice on sostenuto trapwork design

[Dave Nereson]

This is a multi-part message in MIME format.

---------------------- multipart/alternative attachment

  ----- Original Message -----=20
  From: Mark Ultsch=20
  To: pianotech=20
  Sent: Monday, October 01, 2001 9:46 AM
  Subject: request advice on sostenuto trapwork design


  List,
  =20
  I am attempting to rebuild a 1920's 5' George Steck that is missing =
all sostenuto linkage between the pedal rod and pitman.  I'm unable to =
find replacement parts or pictures of the original replacement.  (Thanks =
to you all who looked for me a while back.)  So. . . it appears that I =
need to design some parts.  Being a novice yet, I have a few questions:
  =20
  1.  What kind of pin should be used?  what diameter?  should it be =
plated?  (I can't find anything in parts catalogs.)
  =20
  2.  What kind and size of felt is generally used in the bushings and =
what is the relationship of hole diameter in the block versus the pin =
diameter and felt thickness?
  =20
  3:  Any thoughts on the spring rate of compression spring to be used?  =
Any good sources to purchase these?
  =20
  Sorry if these questions are too basic.  If you have other thoughts or =
concerns I'll be happy to get them.  Thanks all.
  =20
  Mark Ultsch
  Madison  WI

  Trapwork pins are in the APSCO catalog, I believe.  I s'pose a large =
hinge pin would work also.  Bushing cloth -- about the same as for =
damper guide wires.  The spring -- either the coil type or leaf-spring =
type (also APSCO or Schaff) would work, depending how the trap lever is =
mounted under the keybed.  Rate of compression?  Don't go buy a newtons =
per kilogram per second gauge -- just compress it with your hand or foot =
and see if it feels to stiff or too weak.  How far it's located from the =
pivot pin will determine this.  Size of hole -- I would just wrap the =
bushing cloth you're gonna use over the pin you're gonna use and measure =
the overall diameter with a caliper or micrometer.  Then drill a trial =
hole in a scrap piece of wood, tear or cut the cloth into strip 3 times =
the diameter of the hole, pull it through the hole, then push the pin in =
and see if it's too loose or too firm, and adjust drill size up or down =
accordingly -- or the thickness of the bushing cloth, if you have =
several thicknesses.   None of this is all that critical -- just so the =
pedal isn't too stiff or too loose -- look under other pianos, take =
measurements, and copy one.   Usually the pitman and the coil-type =
spring sit in flat-bottomed shallow holes in the trap lever (use a =
Forstner or spade bit), with a similar hole in the keybed for the top =
end of the spring.  Sometimes they're bushed with felt, sometimes not.  =
L-shaped threaded hooks usually go under one end of the trap lever to =
keep the pitman from falling out if a pedal rod or the whole lyre is =
removed.
          Sincerely,  David Nereson, RPT, Denver =20
  =20
  =20

---------------------- multipart/alternative attachment
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/pianotech.php/attachments/43/a2/8f/47/attachment.htm

---------------------- multipart/alternative attachment--