Restoration of a Knabe Concert Grand Page Three
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63) 
64) 
65) 
63) This shows the size of imperfection that justifies steps to be taken for
repair. Nothing this large should be visible in the final finish.
64) These brackets were part of the fall board and had broken. Rather than
regluing them and using them, I reglued them and used them as a template. New
brackets were made from multilaminated birch to prevent them from ever breaking again.
65) Here you see sample parts from Renner being tested on the action frames.
To the right, you see the handbook which contains regulation specifications for most all
piano types. After the closest fit was achieved, the keys were weighed to find out
if the selected action parts would work well in the piano. It was decided that a
compromise was called for. Two different types of whippens were available.
One was spring loaded to reduce down weight and the other had individual hammer rest
cushions. The down weight was found to be 56 grams on the whippens with the rest
cushions. This is about six grams over the specifications that the book calls
for. However, the up weight was also comparably high which will cause the action to
have excellent repetition. Also, the individual rest cushions of the whippens make
for a quieter action. The original rest rail on this piano was made in such a way
that it would resonate slightly each time a hammer shank slapped against it. It was
decided that it was better to deal with the weight problem so that it would be possible to
quiet the operation of the action. Actually a large percentage of artists prefer
action weights as high as 60 and even 70 grams so the few grams of additional down weight
may even prove to be an advantage. It will be left up to the customer as to whether
they wish the down weight to be exactly on the specification marks or a little heavier to
please many of the artists who will be using the piano.
66) 
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68) 
66) This shows the tenor portion of the paper pattern being made for the bass string
maker to use in winding the new strings. See pictures #82-85 to view the new scale
that was decided upon for this piano.
67-68) These pictures show one of the intermediate sanding that was done as the
finish was applied to the lid. The sander in the pictures has a very large surface
area so that the results will be as flat as possible. In addition, the sanding
pattern alternates from left to right and then front to back in order to keep the surface
flat.
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71) 
69-70) After the last of the lacquer has been applied it is wet sanded with 400 grit
wet or dry paper, using an elite rubbing machine which gives a very flat result.
This "pre-rubbing" is done to remove all the spray marks (called orange peel)
and to check for any imperfections that may have been missed. Then the lacquer is
allowed to cure for as long as possible (maximum of one month and minimum of two
weeks.) Once all the solvents have escaped from the lacquer it will receive a final
sanding with 600 grit wet or dry paper and then will be buffed to the desired sheen.
71) This shows the sharps after the old back checks have been removed and the keys
have been restored. The sharps were cleaned thoroughly with alcohol and then sanded
to remove every trace of surface imperfections. Then a durable lacquer was
applied. Just enough grain in the ebony keys was left open to give the performer
some traction during use. The surface of the sharps is now very smooth and shiny but
with a bit of grip for the pianist.
72) 
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74) 
72) These are the new Renner back checks and wires. It was decided
that new wires were to be installed since Renner only sells back checks with the
wires. The new wire will be better able to check the hammers than the tired old
wires.
73) The sharps are done.
74) The key frame is totally restored and new felts installed along with all new key
guide pins. The front punchings are all Renner. These felts were chosen
because of their extra large circumference and density. The design of this piano
requires that there be 12mm of punching under the fronts of the keys so very dense felts
with lots of surface area is required to keep the keys from feeling mushy at the bottom of
their travel.
75) 
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77) 
75-76) The whippens that were selected for replacement had jack tenders that were
angled slightly different than the originals. Therefore, new Renner let off buttons
were purchased. These buttons are longer than the original and will enable the jacks
to contact the let off buttons without the need of moving the let off rails. To have
moved the let off rails may have caused the brackets that hold them to become too loose in
the wood. Also, the larger let off buttons from Renner have much more wood to them
so they will be much more long lasting and almost impervious to breakage even 100 years
from now.
77) Even with Shanks and Flanges made by Renner, it is necessary to carefully
measure the grams of resistance in the hinges (called action centers.) These shanks
are made in three different sizes: the largest diameter shanks are in the bass, the
medium sized shanks are in the mid treble, and the smallest shanks are in the high
treble. This helps the smaller hammers to rebound from the strings more quickly thus
producing more tone. Some of the parts had to be repined in order to keep all the
action centers at the correct tightness. If the action centers (hinges) of the
shanks and flanges are too loose, then the hammers will rebound from the string to easily
causing too many high overtones to be excited. Also, the reduced friction of too
loose action centers will cause the action to feel wrong. When finished, the centers
were pinned with 5 to 6 grams of resistance in the low bass to 4 grams in the high treble.
78) 
79) 
80) 
78) The whippens that were chosen for this action come in two parts - the whippen
body and the heel - which have to be glued together in the shop.
79-80) Mounting the whippens to the rails. Only general attention was paid to
spacing and alignment here. Once the strings are on the piano, the shanks and
flanges have been traveled to ensure they are swinging straight towards the strings and
parallel to each other and the hammers have been mounted, then more care will be taken to
space, travel and align the whippens.
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86) 
81) The keys have been fitted to the guide pins. The new guide pins
are larger than the originals. This means that the fit of the pins in the key frame
is extraordinarily tight. The center holes of the keys now fit the new pins
perfectly. And the bushings have just the right amount of lost motion to ensure
that they won't hang up in humid weather.
82-85) These are charts showing the new scale that has been calculated for this
piano.
86) This is a chart that shows the speaking lengths of the strings. This shows
the problem of the tenor bridge area. The lowest parts of the long bridge should be
longer than the highest parts of the short (or bass) bridge. In this piano is was
not. Therefore, part of the rescaling entailed placing wound strings on the last
five notes of the long bridge in order to give more power to that section of the scale.
This will eliminate the weakness of the tenor section of the piano. Knabes
are knows for weak tenors with their original scales. Another change in the scaling
pattern was to reduce the tension and inharmonicity of the midrange and treble. The
original scale was much too high in tension. While the new scale is still a high
tension scale, the amount of tension has been reduced. This should make for cleaner
octave tuning and longer sustain. Finally, in the bass, the rescaling included a
change in tension when the scale passed from trichords (three strings per note) to
bichords (two strings per note) and monochords (one string per note.) The purpose
here is to have a decided increase in tension and therefore an increase in power when the
scale drops a string out of the unison. This will make it impossible for the
listener to hear any difference in tone or power as notes are played up and down through
these stringing changes.
87) 
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89) 
87-90) These charts show the original scale for this piano. It was not a bad
scale but it did have a few problems.
90) 
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92) 
91) Sorting the tuning pins for size. Tuning pins do vary in size slightly so
to get the most even pinning possible the pins are sorted. Each container holds pins
that are .0005 of an inch larger than the next.
92 - 93) Stringing the piano
93) 
94) 
95) 
94) After the surface of the lid has been rubbed perfectly flat, cauls are placed on
the lid and the rubbing machine is run over the surface using them to ensure a perfect
arrangement of satin lines in the finish.
95) The lid is covered in buffing compound. This is used to clean off all the
rubbing marks before the step described in #94.
96) 
97) 
98) 
96) The completed lid. Note how perfectly the workbench is reflected
in the surface!
97) The inside of the piano is covered so it doesn't get any splatters on it.
The rim is being rubbed out.
98) Note the perfect reflection of the items on the shop floor as they are reflected
in the side of the piano.
99) 
100) 
101) 
99) The completely rebuilt pedal mechanism.
100) Installing the new hammers. These hammers were made by Isaac piano and
are among the best hammers available anywhere in the world.
101) Installing the new damper felts after the stringing was complete.
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103) 
104) 
102) The finished piano assembled except for the lid
installation.
103) The piano was later sold to a customer in St. George Utah. Here you see
the piano posing in its new home.
104) The happy new owners pose with their new instrument.
© Copyright 2010 {David Rodgers' Piano Rebuilding}. All Rights Reserved.