Restoration of a Duo-Art Expression system for Skyp Harmon
31) 
32) 
33) 
31) The tracking mechanism signals have this cut out block
to prevent the tracker from operating during rewind. This is mounted on top of the
valve assembly that signals the expression system.
32) The expression signal box is being taken apart. The brass valve seats to
the left are made in this way so that you can adjust the amount of valve travel very
precisely. It is very important that these valves operate with lightning speed.
For this reason, they are set to have very little travel. Because they have
such little travel, they also have very limited amounts of suction that they supply to the
enormous theme pouches in the expression regulator. For this reason, the valves must
be very tight, their pouches must be very tight and set for minimal lost motion and the
theme pouches they operate must be very tight as well.
33) The valve box is all apart and every piece of leather is being replaced, every
metal component is polished, every wood component is resealed and every external metal or
wood component is polished and painted to be as good as new.
34) 
35) 
36) 
34) The expression cut out block and the other control box
have been rebuilt and the tracking cut out block has been releathered and resealed.
Unlike the expression cut out which is made very much like the tracker cut out box, there
aren't enough screws in the tracker cut out to be able to seal it with the pouch leather
gasket like was used in the expression cut out. The tracker cut out must be wrapped
in pneumatic cloth like it was originally treated.
35) This is the tracking mechanism. It is built upon a carefully balanced
system that must be working perfectly for this to operate. The pneumatic must be
completely air tight and the control bleeds must be free of all dirt or the device will
not operate.
36) All the old cloth has been cleaned away as well as the old hinges.
37) 
38) 
39) 
37) The inside of the tracker is freshly sealed.
Although the wood is dense enough that it isn't necessary to seal it when it was new,
hairline avenues for air infiltration often develop over the decades so I leave nothing to
chance. These all get a good sealing job before they are recovered. You can
see the new inside hinges as well. Outside hinges were not originally used but I add
them to make the pneumatic stronger and more stable.
38) The first half of the tracker is recovered and the second strip of cloth is
precut to fit the pneumatic before it is glued in place.
39) The finished tracker is remounted to the assembly with the valve blocks.
All the connecting hardware has been buffed to a high gloss and screwed back onto the
blocks with a coat of burnt shellac to act as glue to lock them into place more solidly.
40) 
41) 
42) 
40) These are the signal crossovers that screw to the bottom of the action.
They take the signals for the playing notes to the pneumatic stack.
41) The first manifold/crossover has been restored. A new gasket is applied
and also all the nipples were removed, polished and then set back into the manifold with
fresh burnt shellac. This task is not usually done by most rebuilders.
However, since the original sealant was looking questionable, I wanted to make sure this
was done so that no leakage could occur. I took advantage of the fact that I had all
the nipples out to give the wood a fresh sanding to make it look new again.
42) The same from another angle.
43) 
44) 
45) 
43) All the crossovers are now restored.
44) This unit comes with the optional action shift pneumatic. Not all Steck
grands with these Duo-Art mechanisms came with this pneumatic. It is activated by
the user when they select soft play in the spool box. Because the nipple which
supplies this very large pneumatic is so small, it is important that the pneumatic be
extremely air tight or it could eventually develop leakage which exceeded the nipples
ability to suck the air out.
45) Because of its location in the piano, this pneumatic was in particularly bad
looking condition.
46) 
47) 
48) 
46) The pneumatic has been stripped of all its parts.
The stops and bumpers were repainted and releathered. The pneumatic was cleaned up
and the inside sealed well. Now it is being recovered.
47) The finished pneumatic is ready to go. It is so tight that it will
certainly hold up well for decades to come.
48) This spring loaded pneumatic (sometimes referred to in the tubing charts as the
"88 note pneumatic" was also exposed and in horrid condition. The spring
loading had taken its toll on the bushed hinges which were falling apart and sloppy.
The cloth had fallen off so badly that I had to take some pretty delicate
measurements to determine the correct original gap.
49) 
50) 
51) 
49) The 88 note pneumatic has been sealed with burnt
shellac. I used this thicker sealant because I found a visible crack in one of the
boards. While the shellac sets up, I'll start work on the hammer lift pneumatic.
50) The finished hammer lift pneumatic is being tested to make sure it is air tight.
The very wide gap on this pneumatic makes it a real fun one to get air tight.
The cloth doesn't want to seal at the corners unless you slit it part way to help
it around.
51) Regluing the broken parts of the 88 note pneumatic. I am cross laminating
the broken areas to help prevent them from breaking again. They have to be able to
operate over decades under very high spring tension so it is important to make very good
repairs now while we have the chance. In fact, I will let these glue ups set up over
the weekend before going any further with them. You can see that the pneumatic has
been recovered and is in the upper right corner of the photo.
52) 
53) 
54) 
52) The power shut off pneumatic before work began on it.
53) After taking the assembly apart, I always check the contacts with a multi-meter
to make sure all is well. I particularly like to use an ohms resistance test to
prove that the contacts are meeting solidly. This switch tested out beautifully so
it will continue to give good service for a long, long time.
54) The restored shut off. I keep saying this stuff has to be really air tight
but it's so important I'll say it again. This pneumatic is signal remotely and must
act quickly under a very minimal signal of air. If it is too slow, the rolls could
be left flapping while the system winds down. It is important for the sake of
preserving the rolls, not to let that happen. So the pneumatic must be regulated
just right and must not have any leaks.
55) 
56) 
57) 
55) The two pieces of wood (far right and upper middle)
pictured here were both damaged due to the heavy spring tension under which they operate.
I rebushed the middle board and then cross laminated the wood with a veneer of
mahogany. This was clamped up and let set up over the weekend. The right board
was also treated with a cross lamination of a thicker layer of walnut. I used these
woods because I happened to have them handy and they were hard enough for the task at
hand. The piece to the right had to be cut out afresh on the scroll saw and the pin
hole redrilled. Once finished, these were strong enough to hold the spring tension
without developing problems in the future.
56) The finished pneumatic shows how air tight it is. Even though the spring
is trying to open the pneumatic, because the nipple is blocked, it is holding shut.
This means it is air tight. I also have replaced the bushing cloth and the bumper
felt.
57) This is the play/rewind pneumatic. Sometimes, I like to call this
pneumatic the "Lobster" due to its shape when finished. One aspect of this
rebuild that was not told to me when I bid the job was that the two actuator arms on this
pneumatic were broken beyond repair and/or missing entirely. New arms had to be made
as well as new flanges. The original design on these calls for all wood pivot
centers with no bushings. The replacements I will make will be bushed for a smoother
operation and easier restoration in the future.
58) 
59) 
60) 
58) This photo shows the new arms after they were finished.
It took a couple of extra hours to build these arms. The cost of doing this
work may be able to be canceled if the customer can work with me. He mentioned that
he would like to stop in the shop and pick up the parts on his way out to visit his
daughter. If he can pick up these parts so I won't have to pay for shipping, I won't
charge extra for the building of these parts. Even in this photo, the work wasn't
finished. After the entire assembly was finished, I found that I had to make some
changes to the way the arms were made to get the right amount of play in the motion of the
arm that this activates under the piano. I built these to match what was left of the
original but that proved insufficient to get the right tolerances.
59) The pneumatic from the other side before work began on recovering it.
60) After taking all the parts off the pneumatic, I cleaned off all old pneumatic
cloth as well as the original hinges. Then I sealed the inside with a heavy layer of
lacquer. I like to use lacquer because it leaves the wood blonde. On Amphion
pianos, I like to use orange shellac because this is what was used originally.
Aeolians have white shellac and lacquer sealants so I try to repeat this. On this
pneumatic, however, it has been rotten to the point that the cloth was ripped open for
many years. This exposed the inner layers of the wood boards to more outside
air. The result is that the wood turned orange inside even though I used lacquer due
to oxidation caused by the years of exposure.
© Copyright 2010 {David Rodgers' Piano Rebuilding}. All Rights Reserved.