Bridge caps

[Delwin D Fandrich]

----- Original Message -----
From: <Yardarm103669107@AOL.COM>
To: <pianotech@ptg.org>
Sent: March 31, 2001 7:42 PM
Subject: Re: Bridge caps


> Ron:
> You're right on the manner in which this practice became generalized. At
our
> shop, though we have a drill press set up to take bridges to be drilled at
> any angle and depth we like. After pinning (left slightly high, but
totally
> bedded in the bridge, i.e. all the way to the bottom), the tops are filed
> down to a perfectly even height which should be no greater than the
diameter
> of the string which contacts it. This way, we get as much of the pin in
the
> bridge as possible, yet have just enough dimension left for evening out
and
> getting rid excess pin height which leads to energy-leaking.
> PR-J

------------------------------------------

This notion has been presented and elaborated on many times over the years,
yet I've never been able to either find even the smallest shred of hard (or
even soft) evidence presented to back it up. To the best of my knowledge
there are no existing tests -- including my own, and I've tried using some
of the best equipment available during the late 80s -- that proves this one
way or another and couldn't. And, the existing empirical evidence is, at
best, inconclusive. Of course, the vibration analysis equipment is some
better now than it was in the 80s and so some slight energy loss may be
detectable using a couple of hundred dollars worth of it. I question,
though, if the potential losses are that difficult to detect and verify
could they in any way be detectable to the human ear?

Nor, incidentally and while I'm on the subject and already in trouble, is
there any proof that burying long bridge pins deeply in the bridge body
improves the energy transfer efficiency between the strings and soundboard
at all. There is some evidence, however, that using long pins in either new
manufacturing or in general rebuilding work may not be the best practice
unless those longer pins are machine driven. That is, with the pins driven
in smoothly and in exactly a straight line with the hole. When the longer
pins driven by hand (ok, with a hammer, but with a hand driven hammer) there
is more damage done to the top of the hole than there is with the shorter
pins leaving them a bit free to flop around expending some amount, albeit a
very small amount, of energy within pin itself -- as heat due to internal
friction within the pin -- and contributing to any false beating problems
the piano may otherwise have. It is at the top of the hole, of course, where
you want the wood to pin contact to be the tightest.

Yes, I understand that both of these notions are considered 'sacred cows' by
most rebuilders and technicians. I have observed over the years, however,
that when properly grilled and with a bit a salt and pepper, some garlic and
a few other herbs and spices tossed on, sacred cows do make excellent
hamburgers.

And now that I've stirred the pot a bit and fired up the grill, I'm off
again....

Regards,

Del