S&S Upr.Bridge Cap Question

[Brent.Fischer@ASU.Edu]

>List,
>
>I need some help with a Steinway Upright bridge.  I am recapping the top
>treble section of the bridge, (top 17 unisons)   The condition of the
>original cap was so badly split (chowdered!) that it was very difficult to
>locate the bridge pin holes in my mylar pattern.  I made my best guess on the
>top five or six notes.  The split actually extended well down into the root.
> Upon repairing the root of the bridge, I think I may have altered the
>position of my reference holes to locate the mylar pattern.
>
>I have the new cap material in place, I've set the bearing, and I'm at the
>point where I should be marking the location of the pin holes.   Using the
>reference points on the new cap and pattern, I measured the speaking length
>for C-88 at about 1/8 inch shy of 2".
>
>I marked chalk lines to show the location of the center string of each
>unison, and my pattern shows the pin location as dead on the lines or just
>touching right side.  But the line of the three pins per unison is not
>perpendicular to the speaking length of the strings.
>
>Should I take the opportunity to set C-88 at dead on 2 inches?  If I slightly
>move my pattern to allow 2" for C-88, do I also move everything else?  And
>should I consider making the notches perpendicular to the strings, or am I
>getting too caught up in theory?  Since the condition of the original cap was
>so poor, should I use some other method to locate bridge pins?  Thanks for
>any help you can give.
>
>Gordon Large, RPT
>Mt. Vernon, ME

Hi Gordon and List:

  Try precision calipers to square up the notches by placing one foot on
your center string impression and then draw a circle on your pattern, the
outside foot dimension is measured from an original sample. If you are
using a clear Mylar type material a circular impression will be left on
the pattern which will make eyeballing a perpendicular angle to the pressure
bar real easy.
  Try using  a six inch staight edge to accomplish this task. I have just
recently altered the bridge on a Steinway C which has staggered unisons
in the first treble section. The concept is mostly the same as what you
seem to have there.  The string line coming from the tuning pin should be
patterned close to where it comes off the new pin/string placement.

  I have a limited scale design background. I try to achieve a distance
of 1 and 31/32 on Steinway grands, and I am not sure of the upright specs.
Just make sure the pattern sits in a position as to not compromise an
acceptable side-bearing angle through-out the section.

  To me a deviation of small proportions on note #88 is negligible
if the execution of drilling the pin holes and notching the bridges is
accurate and consistent.   Hope this helps.  Brent

====
Brent Fischer, Piano Technician
School of Music, Arizona State University
Tempe, Arizona 85287-0405
602/965-6760 FAX 602/965-2659 Msg 602/965-3371
http://www.asu.edu/cfa/music/