[pianotech] Increasing bridge height

[Will Truitt]

OK, Ron

As I understand it, and I make no claim to have the practical experience and
knowledge of yourself and others who have raise bridge heights over a number
of pianos and years, Steinway bridges tend to be too short in the treble.
They also tend to often lack sustain and volume in that area.  A short
bridge (my example A-2 at note 88 is 25.5 mm) will have less stiffness and
mass compared to a taller bridge; indeed, less stiffness and mass than lower
in the scale on this same bridge, where it is tallest at note 21 at 33 mm.
Yet higher stiffness and mass in the high treble bridge are (among many
other things) properties that (skillfully applied) result in an increase in
treble sustain and volume.  The consensus I have gathered from others who
have experience doing this is that it is generally not necessary to increase
the bridge height by a similar amount elsewhere.  Del has indicated that for
a piano like this A-2, a high treble note 88 bridge height of 30 to 34 mm.
is what he would target.  Where I will put it as a finished height, I can't
say yet.  I am given to understand that raising the bridge height elsewhere
in the scale does not carry sufficient advantage to merit doing so, at least
within this particular context.  Thus, I gather that practitioners taper the
bridge from the increased height in the treble to something approximating
the original values at the low end, and you will end up with a bridge that
is roughly the same height everywhere.  I will decline to give you exact
numbers presently - I don't have enough information from the piano yet.  Let
me reiterate that I have not yet even pulled the wire off this piano and
lifted the plate.  

I am very meticulous in teardown, and take lots of measurements.  I really
enjoy taking a piano apart for the first time, because the piano tells you
its story at that time - the good, the bad, and the ugly.  If you are asking
me exactly what I am going to do, the most honest answer I can give you is
that I do not know because I have not completed the process yet.  I will be
more than happy to share my values with one and all at the time when I am
ready, and hopefully made some intelligent and informed decisions.  If I
haven't, I am not afraid to expose my ignorance because I do not want to own
it forever.  What has now become a long thread here on the forum has taught
me a lot, and I expect to learn more.  

I am a very long way from cutting wood.  I have a lot of time and work
between now and then.  

You keep asking me about whether I am going to raise the bridge and plate
heights in the treble, but I have already stated on several occasions that
is exactly my intention, and what I will likely do.  Yet to be determined is
how much of each.

As for the hammer boring, will I need to taper when it is all said and done?
Maybe, maybe not.  I'll decide when I have a strung plate in the rim and I
retake all my string height measurements.  Very likely that 6.5 mm
difference will shrink substantially, perhaps enough to not need to taper
the bore.  I have bored hammers for 20 years and done it both ways, and am
not married to doing it one way or the other.  I don't think I am
misunderstanding the relationships between hammer bore and the changes in
bridge height that will be made, as you seem to think. I will be dealing
with the bridge and plate height changes as they exist in the reinstalled
string frame before I bore the hammers.  Would I taper the bore for 1.5 mm.
if that is what it ends up being?  Probably not, as I would generally not
consider it significant enough to bother.

I value and appreciate your ongoing input on this subject.

Respectfully yours,

Will

  

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Nossaman
Sent: Wednesday, March 25, 2009 11:23 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Increasing bridge height

Will Truitt wrote:
> Hi Ron:
> 
> I'm at home and not at the shop, so I'm trying to do this from memory.  I
> believe #21 is 193 mm. If you want the rest of the measures at the section
> ends, I'll get that tomorrow.
> 
> "I'm still trying to figure out where you plan to set the plate and bridge
> heights, and why. Are you planning on boring hammers to accommodate what's
> there without changing bridge or plate heights?"
> 
> Changing bridge heights is why I started this thread, and the whole point
> was to explore the ramifications of increasing the bridge height in
targeted
> areas. I'm putting a new board in this piano, and wanted to explore this
for
> the many reasons already discussed.  I have not fixed yet where it will
end
> up, but it looks like I will raise the high treble end from 25 mm to 32 or
> 33 mm.  At note 21 the present bridge height is 33 mm. and I will likely
> make the bridge along its length fairly consistent in height.  I will not
be
> using vertical hitch pins, however, so the finished bridge heights will
have
> to accommodate targeted downbearing values as well as the curvature of the
> plate. I still have not yet pulled the plate as I have just begun
teardown,
> so I have a lot more groundwork to lay before I know where my feet are. 
> 
> It's premature for me to try to get into the whys and how much, as I am
> still learning as much as I can before proceeding (and I have learned a
> great deal from all of you so far, THANK YOU VERY MUCH!)

But the whys and how much are exactly what you need to 
determine before you start cutting wood.


> Whatever values I end up with on the finished bridge, I will still likely
> end up tapering the bore, The bore will be derived from the measured
string
> heights of the strung piano after all modifications.  The taper could at
> least be partially mitigated if I end up tilting the plate down in the
bass
> and up in the treble to help level the string plane out (as Jude has
> suggested). I will likely be changing both plate and bridge heights, so
> obviously the original string heights serve only as a starting point and
> frame of reference. 

Have you determined what you'll end up with in string height? 
If you raise the treble end of the plate to accommodate a 7mm 
bridge height change, you'll end up with something like a 3mm 
or less change throughout the string height for the long 
bridge, with about a millimeter difference from #21 and #88.


> I don't know if it matters if the bore is a tad shorter or longer.  What
> qualifies as a "tad"?  Does 6.5 mm. difference within the treble string
> plane qualify as a tad?

Where's that 6.5mm difference after you raise the treble end 
of the plate? That's my point. You are, or you aren't raising 
the bridge height and plate there. If you aren't, you deal 
with that height difference. If you are, you won't. Figuring 
the hammer bore as if you weren't changing bridge and plate 
height doesn't much reflect what it will be when you do, does 
it? Do it or don't do it, but but work with the appropriate 
set of figures either way. In this case, a tad is in the 
middle of the 3mm or so variation between #21 and #88, which 
would be around 1.5mm. I personally don't find it necessary to 
waste time tapering the bore for that little difference. If 
you do, go for it.


> "Play better".  I can't speak for Bruce Clark, and it would not be fair to
> attribute this to him verbatim as what I quoted is my second hand
recounting
> in my class notes.  I think it would be best to leave the explanation of
> that to him at another time.  

Best left unsaid then, until it can be backed up with 
something rational.
Ron N