Restoration of a Knabe Victorian Grand and its transformation to a Pianomation player
piano for Don Hollingshead
106) 
106a) 
107) 
106) Now the long bridge is placed over the fitted ribs and
set so that it is exactly in the position it will occupy after reassembly. Then
marks are made directly on the ribs to show where the long bridge will pass over them.
I will then shape the ribs so that they have the proper crown built right into
them. I set this crown in such a way that the highest point on each rib is as close
to being directly under the long bridge as possible. My jig that is used for shaping
the crown on the ribs has an indicator mark that shows me where to align my marks on the
ribs so that the jig will shape them accordingly.
106a) A photo of the process of shaping ribs so that they will be crowned and also
set to be highest directly under the long bridge. A router is used to cut this shape
into the ribs.
107) After the ribs have been crowned, I clamp them to the old sound board and trace
the shapes of the original ribs onto the new ribs. Then the shape is rough cut on
the band saw and fine tuned at the sanding station.
108) 
109) 
110) 
111) 
108) The ribs are now set back into the piano and fine tuned
by hand until they fit perfectly flush into the notches.
109) Using a custom made jig, I am in the process of making a new bass bridge for
this piano. The original bridge was still very solidly built and intact but its
design did not meet the highest modern standards. The original bridge was made of
solid maple. I have custom cut strips of hard maple which I am gluing up with West
System epoxy in order to create a very strong vertically laminated bridge which will last
longer than any other type of bridge can and which will transmit vibration from one string
to the next and from all the strings into the sound board more efficiently than the
original design permitted. I had to custom cut the wood for this; not using stock
material I had done already for the rest of the pianos on the current rebuilding cycle due
to the extreme height of this bridge. In fact, I am strongly considering adding
additional "meat" to the thickness of this bridge and then drilling out relief
holes in strategic areas in order to lighten the bridge. This will provide for
maximum vibration transmission while maintaining maximum vibratory amplitude. This
is a technique usually seen only in the finest German made pianos like Bösendorfer.
110) A special jig that I use for making vertically laminated bridges is called into
service. The jig is cut out to the exact bridge curve of the piano I'm currently
working on. The form is lined with thin plastic to keep it from gluing itself
together and then the layers of vertical grain maple are coated with West System epoxy and
placed into the jig. Then the entire assembly is carefully clamped down until it is
under tremendous pressure. Once the epoxy has completely cured, the new bridge core
can be removed and will hold its shape exactly as set up in the jig with no springing back
whatsoever. After this, I will glue the jig back together again so that I can cut a
new shape out of it for the next bridge. Occasionally, I make an entirely new jig
when the old one has been cut out and glued back together too many times.
111) The complete vertically laminated bridge core is a perfect match to the
original. It will be a better bridge than the original which was made from solid
wood. The cutting of a long bridge from a solid piece of wood means that many of the
wood fibers are cut as the straight grain runs off the pattern for the bridge's shape.
The vertical lamination technique keeps the grain of the wood running straight down
the full length of the bridge making it a much more vibrant entity.
112) 
113) 
114) 
112) Gluing the quarter sawn hard maple cap to the top of
the bass bridge. The original bridge had a very thick cap (an inch thick or more)
then a glue joint to the core or bottom of the bridge. The new bass bridge has a cap
of good thickness but not so thick that the metal bridge pins won't be able to penetrate
through to the core. The pins must contact the core in order to get the strings'
vibrations deep into the bridge where they can be properly amplified.
113) The quarter sawn hard maple cap has been cut out and is now being glued to the
treble bridge core which is vertically laminated. Now that the core is out of the
press and is the same shape as the original bridge, it must be glued to the cap on another
jig which will impart the appropriate amount of crown to the long bridge. Just as we
went to great lengths to pre-crown all the ribs, the long bridge must also have its crown
built into it. This will make the entire sound board assembly more strong and
durable. It will also increase the power of the tone of the piano. Most
rebuilders do not take this step into their own work. They glue up the long bridge
totally straight and bend it to the sound board later. I believe this adds undue
stress to the glue joint between the bridge and the soft spruce of the sound board.
Far better to create the crown by using the maple to maple joint of the cap to core.
The long bridge has its new cap glued into place with West System epoxy. I
like the epoxy for its acoustic properties but I also like the fact that it is totally
impervious to moisture. These glue joints that I am making in this bridge will be
forever. No amount of moisture exposure can ever cause them to come apart.
Other joints that must be reversed in the future (such as the joint gluing the sound board
to the piano itself) will be done with acoustic glues that are effected by moisture.
This way the sound board can be replaced again in the future with little harm to the joint
with the piano. In the future, if this new cap wears out and must be replaced, it
can be machined off the vertically laminated core and a new one installed just like usual.
The vertically laminated core will outlast anything out there due to the quality of
the wood, glue and techniques used in its manufacture.
114) The completed treble bridge "blank." It is ready to have its
length custom fitted to the original bridge, index marks transferred, thickness and
drilling patterns transferred onto it and carried out. Some of this work is often
done later after the bridge has been glued into the piano. I feel I do better work
on these bridges with them on the bench where I can reach them easier and can get better
power tools onto them. Once in the piano, all further work to the bridge has to be
done by hand. I have done and can do it this way but have come up with a system of
working which will yield better results while working outside the piano.
115) 
116) 
117) 
115) Many rebuilders would take this bridge blank and glue
it to the sound board just as it is and carry out the rest of the work after the sound
board was glued into the piano. And they are quite correct to do this.
However, the reason they do this is because they want to check the bearing levels for the
strings with the assembly glued into the piano and the plate lowered into its final
place. They can then mark the bridge for height and plane it to the correct height
for the sound board and also mark the locations for the bridge pins based upon the
locations dictated by the plate. This is a quite good way to proceed. However,
I have certain beliefs about this process that cause me to feel this work is better done
outside the piano; at least by me. First, this is a Mason and Hamlin which means
that the original bridge dimensions were certainly perfect from the factory. Any
minor adjustments to down bearing that I feel may be needed can easily be done using the
original bridge and adjusting the plate height and plate felt thicknesses. Every
factory has to make sure their bridges are the correct height or the pianos won't work
properly. Even if the factory were to make mistakes, they are always minor enough
that they can be corrected by plate height, sometimes shimming duplex bars and felt
thicknesses. I am personally much better able to plane bridges squarely, mark bridge
pin locations accurately and drill and notch bridges precisely with the bridge clamped to
a bench where I can see it and get at it more easily. Once it is in the piano it
becomes very hard for me to work on with precision so I do this work outside the piano.
My first job is to measure the thickness of the original bridge down to the nearest
thousandth of an inch all along its length. These measurements are precisely
transferred to the new bridge and then the bridge is planed down by hand on the bench
until every inch of bridge matches the original for thickness exactly. That task has
just been completed in this photo.
116) The next step is to take a pattern from the original bridge of the locations of
all the bridge pins. I start with index holes which are drilled into the bridge and
help me to align the bridge pin locations and the sound board to get everything aligned
properly with the plate. Then I use a soldering iron to burn a little hole through
clear mylar which has been pinned to the bridge. These holes become my locating
marks onto the new bridge. The pattern, once made, is moved to the new bridge and
the index holes lined up. With some bridges it is necessary to "figure
out" where the index holes belong based upon several different other measurements.
The best way to index a bridge is to drill a hole through the bottom of the sound
board, through the bottom of the bridge right up through the top. However, if this
hole isn't perfectly square to the entire thing (which it seldom is) the marks will not
help much in the transition to the new bridge. For this reason, I prefer to use my
best judgement and numerous measurements all over both bridges to find the best place to
locate the pattern. The bottom index holes that align the bridge to the sound board
are easily transferred with accuracy by cutting a slice off the bottom of the old bridge
and taking it over to the new one and lining it up. With such a thin slice, angles
in the index hole will not have had a chance to telescope out and make anything
inaccurate. The most important thing to get right when doing this is the locations
treble to bass of the pattern and the length of the strings at note 88. Most pianos
have a 50mm length to their highest note. Some will go as high as 55mm but they
seldom go less than this. It is important to keep this measurement correct or the
tone of the treble can be compromised. A few millimeters discrepancy in the bass, on
the other hand, has little to no effect on tone as long as it is just in the length of the
string that the difference occurs.
117) The pattern is now transferred to the new bridge.
118) 
119) 
120) 
118) Back to the bass bridge to finish up. These two
photos show the bass bridge after it was completed. The first photo shows the bridge
after the pin holes had been drilled, the top lubricated and the edges chamfered.
The second photo shows all the bridges I am currently working on after they were finished
and the sealant coat put on them.
119) Here, you see the long bridge has had its pin holes predrilled. A special
collar is custom made to fit over the drill bit. The collar is made from wood that
is slightly softer than maple to prevent it marking the wood at the top of the bridges.
Still, it does leave a slight mark that actually goes away after burnishing,
notching and pinning. The reason for this wooden collar is to prevent the drill
itself from making contact with the bridge. Of course, I could just stop the
drilling before the drill hits the bridge. However, I want the holes precisely the
same depth each. I want them a specific depth which permits me to drive the bridge
pins all the way into the bottoms of the holes. The tips of the bridge pins will
seat into the maple and make better sound transmission. Also, with the holes all the
same depth, I can get the bridge pins to the same average height across the bridge for a
nice cosmetic result. The normal way to do this job is to drill the holes too deep,
drive the pins in on the shallow side and then grind them all to the same height with a
file or belt sander. This gives a good cosmetic result but compromises tone a
little. This way of drilling enables me to not have to grind the tops of the pins at
all. This makes for a better tonal result at the same time it produces a very
special cosmetic result.
120) The top of the long bridge has received four coats of McLube. This is a
special lubricant which can be burnished to a nice, soft gloss and makes the top of the
bridge very smooth and even slippery for better tuning stability and a good cosmetic
result.
121) 
122) 
123) 
121) The next job is to notch the top of the bridge so that
the strings will clear the bridge on their way to meeting the bridge pins and also to
ensure that the strings hit the wood of the bridge in the same plane as they hit the
bridge pins. This prevents false beats and increases sustain. The first task
in notching out the excess wood is to carefully cut saw kerfs into the wood down to a
pre-marked depth. The mark is made on the sides of the bridge and the saw cuts are
made just to the line. When the chisel removes the excess wood, the saw kerf will
keep the bridge from splitting in places we don't want removed. A round razor cutter
is then driven into the saw kerf to cause it to take a rounded shape near the pin holes.
This will be the shape the chisel will make so it further prevents splitting.
122) The bass bridge has received its new bridge pins. After it is glued to
the piano, a final coat of lacquer will finish dressing up the appearance. Because
this shot was over-exposed, I had to wash it a number of times through software to get it
looking better. This magnified some areas of the wood which have been sanded; making
them look uneven. They aren't uneven and will be even better yet once they've
received a coat of lacquer.
123) Now I carefully notch out the long bridge to match the original. To do
this job right, requires a chisel which is razor sharp. It is necessary, actually,
to resharpen my chisels about three times for each bridge. I use the curved shaped
knife to help me get a clean curved shaped cut. To sharpen these tools, I use a
diamond stone and a special jig. After rough sharpening them on a course stone, I
fine tune them on a very fine stone. Each side of the chisel's cutting edge is
sharpened on the stone until a fine wire edge is drawn up on the opposite side. Then
the chisel is flipped and the other side worked until the wire edge comes up on the
opposite side. Then the chisel is buffed on the polishing wheel to clean off the
excess metal on the edge and point the sharp wire edge toward the cutting direction.
This process is repeated, as I said, three times for each bridge. I wear a
very clean glove on one hand as I work to keep my hand oils from soiling the freshly cut
wood and to protect my hand from the nice clean edge I've created on the corners of the
bridge. After the notches are all cut, I will seal the notched areas with an epoxy
sealer which forms a beautiful finish with just one coat. The rest of the bridge
will be finished solely with lacquer. Then the bridge pins will be driven into place
and the bridge will be ready to glue to the new sound board. A basic cut out is all
that is needed to make the bridge function well. The real important part is that the
notch begin its path down exactly in the center of the bridge pins. This prevents
false beats. Many companies do not give much attention to getting the notches
looking extremely neat and uniform. They just knock off the edges any way that is
convenient and leave it go at that. Even this piano did not have perfectly uniform
notches across the length of the bridge. I give great care to making each notch
resemble all its neighbors as closely as I possibly can. The finished bridge will be
neater looking cosmetically than the original bridge was!
124) 
125) 
126) 
124) Now all the notching is complete. The final
shaping of the bridge has also been completed. This shaping includes the tapering of
the bass of the bridge to match the original. The purpose of tapering the bridge is
to make the surface which glues to the sound board straighter than the bridge is on its
own. The sharp bends are taken out. Also, the treble area is thinned to leave
more sound board area free from being glued to a bridge so that more spruce will be
available for free amplification. This also gets the edges of the treble part of the
bridge farther away from the rastin to keep the bridge from becoming too rigid. Much
rigidity in the upper treble is desirable but too much will reduce the sustain and power
of that section. Higher pianos of a later point in history (the Mason and Hamlin
specifically comes to mind) used a somewhat "beefier" cross section to their
bridge than this piano possessed. To make the tone production of this piano better,
I opted to keep the bridge a little more bulky than it was originally. This should
facilitate better sound transmission and better bridge pin retention than the original
bridge possessed. The accompanying photo here is of all the bridges I've built in
the time I've been working on the bridges for this piano. I have five pieces I was
working on at the same time and all their bridges are now made new and pictured here.
To make for a really nice cosmetic look, the bridge pins I used were nickel plated.
For better tone production, these bridge pins are slightly over-sized compared to
what was used originally. And as a final nicety, I did not have to grind the tops of
the bridge pins down to get them consistent since I took great care to make them come out
even without doing this. The bridge pins are more rounded and the nickel plating is
preserved. This makes it less likely that you will get anything caught on the pins
when cleaning the inside of the piano, it ensures that the ends of the bridge pins will
not rust if the piano is asked to live in a moist environment and the final cosmetic look
is very slick.
125) The sound board has finished drying in the hot box. Now the panel is laid
over the piano and the shape of the case traced onto the wood from beneath. The wood
will be cut out too large to leave room for final fitting. The panels are ordered
square because I like to be sure I have enough wood. When ordering them precut to a
grand piano shape, it can get a little tricky if the precut panel is on the small side.
126) The shape of the piano which was traced in pencil onto the board is then
retraced with a very sharp knife. This cuts the surface fibers of wood so that the
saw will not cause splinters to run into the area of wood which we will be keeping.
127) 
128) 
129) 
127) After the general shape is cut out, the board is put
into the piano over and over again for as long as it takes to get the fit really good.
The idea is to have the edge of the sound board meet the rim of the piano.
This helps to reflect vibrations back into the board rather than letting them be
dissipated as a poor fit would do. Any tiny discrepancies in the fit that remain are
so small that the glue squeeze out will fill them completely when the board is glued into
place. Knabe was famous for leaving a quarter inch gap between the board and the
rim. They claimed that they did this to make the board more flexible and improve
tone. However, we thin the edges of the boards (a process called diaphramizing) to
increase flexibility. The gap left by Knabe (in my opinion) had nothing to do with
flexibility and everything to do with laziness. I did such a good job of fitting
this board that I felt it deserved two photos. I worked on fitting this board two
days. I wasn't working it all of both days but I did work the board so long each day
that I finally had to quit and put it back into the hot box because I could tell it was
starting to grow a little. When moist air comes into contact with a dried sound
board, it begins to grow slightly within just a few hours. The growth isn't much
being just a number of thousandths of an inch but it is enough to throw off my
measurements when fitting the board; so I divided the job into two different days so I
could spend more time with it.
128) A jig is being made to show me the exact location of the termination bar or
dead bar. When I thin (diaphramize) the sound board to make it more flexible, I will
want to align my thinning process with the edges of the speaking area of the board.
The corner is blocked by this bar and not part of the vibratory surface. I will use
a router to cut a decorative channel just inside of where the sound board joins the dead
bar. This will make the board flexible in the required area without the need of
thinning the corner which does not need to be thinned.
129) Aligning the old board to the new one using my index marks and transferring
landmarks.
130) 
131) 
132) 
130) The template I made from the uniquely shaped
termination or "dead" bar is clamped to the sound board's top and used as a
guide for the router. The router cut a rounded groove which will serve to free up
the vibrations of the board in this area; enriching the overall tonal production of the
piano.
131) Now the new board is marked along its edge for the diaphramizing process.
This thinning process makes the sound board more flexible along its edges.
The first step in this thinning process is to mark the edge of the board appropriately as
a guide. Then a fine toothed saw is used to make angled cuts into the board.
They go down to the mark on the edges and taper off to nothing at about six inches.
The goal is to line the thinning up with the places where the ribs thin out as well.
All edges of the board are thinned except those near the upper section of the
treble bridge. This area requires the board to be thicker for better tone
production.
132) The first step is to use a block plane to remove the bulk of the wood down to
the marks. Then a smoothing plane is used to clean up the marks left behind by the
block plane. Finally, a sander is used to do the final cleaning up and smoothing.
133) 
134) 
135) 
133) The board is now ready to be indexed to its ribs and
glued up in the sound board press.
134) Gluing the ribs to the sound board.
135) Here, I am rough planing the shaped profile into the ribs of the sound board.
© Copyright 2010 {David Rodgers' Piano Rebuilding}. All Rights Reserved.