[pianotech] Making bridge caps was RE: Piano topic

[Encore Pianos]

Thanks, David.

 

Much appreciated, 

 

Will

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of David Love
Sent: Monday, October 24, 2011 9:06 PM
To: pianotech at ptg.org
Subject: [pianotech] Making bridge caps was RE: Piano topic

 

Will:

 

I thought it might have been your post but couldn't find it either.  Anyway,
the procedure I've outlined is designed to predetermine the thickness of the
cap and then either plane the cap from the bottom to the desired thickness
or cut it and sand it on a flat belt sander (one section at a time).  I
don't like to plane the bottom of the bridge root because on a Steinway (and
some others) it has a curved contour similar to the crown of the piano and
it's difficult to keep that and I don't really like to alter that.  Also,
when taking material from the bottom of the bridge root, unless you are very
careful it's easy to get things out of square.  Then your careful setting of
the plane of the bridge cap can be ruined or you will have to make some
compensation.  Moreover, the logistics of planing and checking the bottom of
the bridge root are difficult when compared with premaking the bridge cap to
the proper thickness in the first place.  I use this method, btw, when
making any bridge cap whether laminated or not.  

 

To determine the thickness of the cap I use gauges as pictured. 

 



 

The larger gauge is used to determine the thickness of the cap.  It is
calibrated incrementally to measure the thickness in millimeters at any
given point.  The width of the gauge is equal to the average spacing between
the bridge pins, about 18 mm +/-.  The smaller gauge is used as a reference
for the distance bearing.  It's calibrated the same way.  The width is
unimportant.  

 

The procedure is quite simple.  I do this with the bridge root already
attached to the panel and the panel already installed in the piano (glued
in).  However, if you prefer to do everything as a dry fit that's fine too.
I don't prefer that even though it's physically a bit more challenging to do
everything with the panel installed but that's my choice.  I like to have
everything glued in and set in it's permanent position when determining
bridge cap thickness and bearing.  The board at this point is conditioned
(with dampp-chasers) to the lowest reasonable EMC that you think it's likely
to encounter in it's final home.  Here in northern California that means
about 35% RH.  YMMV.  I just want to be sure that during the drier season I
don't go negative.  

 

Install the plate and secure it with the nosebolts and a few pinblock
screws.  You should have established the plate height already.  I wedge the
board down very gently just to take out a bit of slack.  Not forced down but
just gently work a couple of wedges between the struts and the bridge root
with a light pounding on the panel.

 

Stretch your string through the capo or agraffe depending on which section.
Use the small gauge to establish your distance bearing which I set at 1.5
degrees throughout (slightly less in the bass but this is for another
discussion).  Recall that the distance bearing will be sine of the angle
(sine of 1.5 degrees is about .026) multiplied by the distance from the
front bridge pin to the point at which the string rests behind the bridge.
If that's 100 mm, for example, then your distance bearing will be 2.6 mm.
I'm assuming we know that.  As I mentioned, how much distance bearing to set
is for another discussion.  

 

Once the string is stretched through the capo or agraffe and resting
comfortably on the small gauge establishing the distance bearing, you then
slide the larger gauge on top of the bridge root and underneath the string
until it just touches the string.  The calibration numbers at the point at
where it touches tells you the thickness of the cap that will be required at
that point.  If you wish you can also use a calipers to measure the distance
of the string over the bridge root.  At the point at which the gauge touches
the string on the speaking side, there should be a small gap at the back of
the gauge.  Ideally, once the string is lowered toward the string rest it
should touch the back of the bridge when it is about halfway down, thus it
should do the same on the guage.  If it doesn't you can angle the gauge to
determine the difference in thickness between the front and the back of the
bridge cap.  For example, if the string touches the back of the gauge at the
same time as the front, you will have to angle it so that the string crosses
the front of the gauge at, say, the 8 mm mark and the rear at maybe the 7 mm
mark.  That tells you that the bridge cap will have to be a bit thicker at
the front than at the rear.  It's an easy way to make that determination.
This will be very usefull to know on the bass bridge where the thinning of
the panel often means that the back part of the cap will actually need to be
thicker than the front.  

 

Make these measurements at several places in each segment of the bridge cap
(3 or 4 in the capo sections and maybe 5 or 6 in the tenor section, etc.).
Then you can plane your bridge cap segments accordingly and fine tune the
thickness with a bench belt sander taking material from the bottom of the
cap.  Once I determine the thickness that I need I actually make the bridge
cap 1 mm taller than my measurements called for.  It's relatively easy to
shim up the string rests or even raise the plate fractionally (I use the WNG
permiter bolt system).  It's a pain if you find that you are just a bit too
low and lowering the plate is a problem (which it sometimes is).  

 

Once you have determined the thickness of the caps measure with a digital
calipers the front and back side of the bridge root relative to the
soundboard panel and add the thickness of the bridge cap to that and write
the overall height of the bridge on the soundboard panel on both sides of
the bridge.  That gives you a reference point to check your overall
measurements later once you've got things glued up.  Don't write these
numbers on the bridge root because you will be gluing the bridge cap over
them!!! (I actually did think of that before making that mistake-getting
smarter)

 

My own procedure (I don't routinely use laminated caps) is to rough cut the
segments to the proper thickness plus some on a band saw and then sand on a
bench belt sander to the final height going slowly and measuring frequently.
I often leave it just a tiny bit high and then sand to the final height once
the caps are glued on.  If you are doing a lamintated cap and your
laminations are thick enough (say 3 mm or so) then you can do the same thing
leaving the last .5 mm or so to be done by hand in the piano.  With laminted
caps rather than the band saw it is probably easier to do the initial
thicknessing with a planer cutting from the bottom until you are close to
the final height and then taking them the final distance on the sander.  

 

I started doing this because I hate cutting those stupid little slots in the
bridge and trying to figure out when the string touches and where and at
what point and going back and forth with files and all sorts of other
useless implements.  Of course for laminated caps you can't cut those little
slots and must find a way to predeterine the height or plane the bottom of
the bridge root.  For reasons already mentioned, I prefer to avoid planing
the bottom of the root.      

 

 

David Love

www.davidlovepianos.com

 

 

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Encore Pianos
Sent: Monday, October 24, 2011 3:38 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Piano topic

 

HI David:  

 

I think it was me, and it was a lot longer than a month ago.  I can't find

my copy either.  But I would still like to ask the question.   I thought I

remembered seeing a post by you some time ago, whereby you have a laminated

cap of established thickness, and you want to set bearing to particular

values.  Since the horizontally laminated caps don't lend themselves to

planing in the fashion you would a quartered solid cap, what is your process

where you are planing the  top of theroot to set bearing, and then gluing on

the cap, ending up with a combination of the cap and the root thickness

where you arrive at the the bridge height that gives you the bearing you

want?  I don't need bearing values, but a description of your process.

Thanks.

 

Will Truitt

 

 

-----Original Message-----

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf

Of David Love

Sent: Monday, October 24, 2011 5:19 PM

To: pianotech at ptg.org

Subject: [pianotech] Piano topic

 

I know this is a bit off topic (it's about pianos) but somebody posted a

comment or questions about a month or so ago about putting on laminated caps

and then setting the bridge height by planing the bottom of the bridge.

Anyone have that original posting.  Don't know if it wasn't a sidebar to

another subject.  I drafted a response but didn't attach it to anything and

forgot about it until just now.  

 

David Love

www.davidlovepianos.com

 

 

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