Rebuilding the Gulbransen
By Bob and Sonja Lemon
Several people have requested information on our version of Gulbransen stack rebuilding. The information contained here should be combined with the information contained in the Art Reblitz book, "Rebuilding the Player Piano".
We favor Reblitz' second version of cutting the stack apart because it does less damage to the channels in the decks.
After removing the hardware and drilling the 4 bolt holes we use a 24-inch to 30" length of 3/4" thick (approximately) x 2-1/4" or 2-1/2" wide straight-grain hard rock maple to remove the pneumatics. To prepare this board for the task, first use a Forstner bit to drill a shallow hole at one end of the board. The hole should be the same diameter as the valve cap and about as deep. Then cut off the end of the board so that the pre- drilled hole is cut exactly in half and at right angle to the long edge. (The pre-drilled hole is used to capture the valve cap for removal.)
Before any further disassembly, be sure to measure accurately the distance between tiers, and check the size of the pneumatics. Sometimes the end pneumatics and those near dividers or support blocks are just a shade narrower than the others. Record this information and take pictures! They will come in handy later.
Either stand the stack on end on a concrete floor, or lay it on a solid bench against a bench stop. Place the end of the maple board firmly against the SIDE edge of the first pneumatic and, with a small sledge hammer, give it a sharp rap. This should loosen the pneumatic. If not, try again. (There is no need to tear the pneumatics apart first.) Do be sure your maple is firmly against the deck before rapping it. Remove the loose pneumatic and proceed along the tier. Be careful of the exposed valve stems! The grain orientation of the pneumatic wood helps prevent the boards from splintering with this method. When all the tier boards are cleared, turn the maple board over so the half circle cutout can be placed over the wooden valve cap. Check the grain orientation of the caps and record the information. Slide the maple board over the cap, still working from an end of the tier, and give it a sharp rap. (Do not knock caps off from the front-to-back position.)
Follow Reblitz' #2 version to cut stack apart, and be sure to measure accurately distance between tiers first! Use a very sharp saw blade. Using a sample board, make a shallow cut in sample so you know exact size of the kerf, and then cut the stack. Remove remaining glue from the stack boards with an iron set to full heat. Place the iron over the glue, which will cause the glue to boil and foam. Scrape it clean, but do not scrape wood away. Be especially careful around the valve cap holes because damage makes it hard to cap the valve hole later.
At this time, prepare the trunk boards for re-assembly. Make maple shims of exactly the right thickness to slide into the sample board saw-kerf without excess pressure. Use straight-grain hard maple for the shim. This shim can be a little wider than the trunk board. Glue one of these shims to the lower side of the middle section of the trunk board. Glue the second shim to the lower side of the upper trunk board. Be sure to use plenty of glue to avoid leaks in the control channels. After the glue is dry, the channels can be drilled out. Working from the top, drill down ONLY through the channels that will extend to the lower decks (from top - 2 of every 3 holes, and from the second deck, 1 of every 3 holes). Use a backup board to avoid tear-out when drilling. *Double check*, *triple check* to make sure which holes go through!
Now, back to the pneumatics: *measure and record the width of the old pneumatic cloth.* Peel off as much cloth as possible. Start at the open end and peel towards the hinged end. The remaining glue and cloth can be removed with a hot iron and scraping. (NOTE: We avoid power-sanding the edges, if possible, because it is too easy to distort pneumatic size.)
To remove the old pneumatic cloth or leather pouch in the well, use a modified Forstner bit (with the center spur/point either removed or drastically cut back). Avoid removing wood, if possible, to maintain the pouch depth. We re-pouch with extra thin (.008-.010 inch) pouch leather and seal the pouch. Be sure there is sufficient dip to the pouch so that, when inflated, the fiber disk will rest solidly against the deck board and the pouch still will have contact with the fiber disk equal to the area of the valve button. If not, the valve will not properly seat when the pouch is inflated.
Before recovering the pneumatics, use one stationary board to mark the *exact* location where pneumatics are supposed to be glued back to the stack. Alignment is most easily accomplished by setting a small ball bearing or BB in the bleed channel hole on the deck and laying the matching hole from the pneumatic board over the bearing. Use a square to align the pneumatic. If need be, the hole in the pneumatic board can be counter sunk just enough to allow full contact with the deck board.
Recover the pneumatics. Use either hot hide glue or fish glue and the next rebuilder will thank you! After cloth is glued on, you will get better penetration of the glue if you touch the edges of the pneumatic to a warm ("synthetics" setting) iron and smooth it with your finger. Just warm it enough to re-melt the glue. Check the corners to make sure they are secure. After trimming the pneumatics, and installing the new pouches, lap-sand the stationary board to assure there is no glue or cloth to prevent good contact with the deck board. CAUTION: Power belt sanders cause inflation of pouch, and partial removal of the pouch. All pneumatics should be checked for tightness before gluing to the decks.
PNEUMATIC INSTALLATION: Use ONLY hot hide glue -- NO clamps are needed to hold the pneumatics (clamps can cause pneumatics to slide out of place). For this job, we use hot glue at approximately 180 degrees F and at the consistency to allow jelling within a few seconds. We also preheat the deck to be glued with a warm ("synthetics" setting) iron. Place the iron on deck and move it along as you add pneumatics. Apply glue to the pneumatic and place it in the marked location. Squirm just a little while pressing firmly. IMMEDIATELY lift the pneumatic off the deck and check for complete glue coverage on the deck and also check to be sure the bleed hole is not plugged. If more glue is required, apply to pneumatic and check again. Press pneumatic in place firmly and hold until the glue sets -- a few seconds. IMMEDIATELY blow through the bleed control channel in the trunk board and check for sound of moving pouch. Use a brass nipple with a foam seal in the end of a piece of tracker bar tubing. Do not blow too hard. This part is most critical! The weak links in this operation are between the pouch well and the bleed hole, and the space between the bleed hole and the back of the pneumatic. This is why every pneumatic MUST be checked during gluing.
After all the pneumatics are glued to the first deck board, recheck all control-air passages for operation and air tightness. Then go back and check that there are no leaks between the pneumatic and deck boards. (For this, you will need to make a device that will seal the valve chamber. We use a 1-1/2" fender washer for backing, with a same size 1/4" closed cell neoprene glued to it. Add another 3/4" diameter neoprene punching to the center of the first piece. This gives a step-down effect. The second piece will seal the inner valve seat.) Then pump the pneumatic to check for leaks. If tight, the pneumatics will not close. If it fails the test, you can still get the pneumatic off if the glue has not dried. Repeat the process for the next 2 tiers.
Rebuild the valves as per Reblitz's instructions using thin pouch leather. We recommend not gluing on the top valve facing before the calibration process. This allows you to choose the best thickness of leather for the job. You want to use the thinnest possible leather facing on the inner valve face (.008 to .010 inch). To get that thin bead of glue around the outter edge of the valve button, we apply a small amount of liquid hide glue to a glass plate, then dip the end of a piece of brass tubing or a wrench socket (same diameter. as valve button) into the glue, and then press it to valve button and place the glued side of the button to sheet of extra thin pouch leather. When dried, a proper sized punch placed over the button cuts the leather for a perfect fit. Small 1/8" punchings of buckskin can then be glued to the center of the leather and the stem glued to that. (Buckskin is the best material for the dot.)
Place the valve assembly in the well, making sure it seats on the inner seat and is not held up by the pouch. *This is a critical adjustment.* (Use a little suction under the pouch.) If the valve moves then the stem is too long; try another valve assembly or shorten the stem. Lay a thin precut leather punching on top of the valve button; valve cover, then dial indicator. A short length of tracker bar tubing with a brass nipple will allow you to puff up the pouch (lightly) and gauge the valve travel. If correct travel (0.300 +/- .002) cannot be achieved with the leather, add paper spacers under valve cap. Apply glue to the necessary parts and recheck. Because the valve buttons are of varying thickness, you will have to play around to achieve optimum settings. Be sure to orient the grain of the valve cap properly if you are using the wooden valve covers. Fiber valve covers will stick better if they are lightly sanded (scuffed) on the mating surface and glued down with hide or fish glue.
DIAL INDICATOR: You will need to make a support for the dial indicator which rests on the valve cap. Use a 3/8" ID lock collar soldered to the small end of a 7/8" to 5/8" copper tube reducing coupling. Drill a couple of 1/4" holes in the side of the tube for air venting. This allows its use when testing valves under actual operating conditions. If possible, remove the return spring from the dial indicator -- not the needle spring. This removes the excess pressure on the inner valve and gives a truer reading, but is not required when testing a Gulbransen. Slide the stem of the dial indicator through the 3/8" lock collar and lock in place.
When the pneumatics are glued on and checked, and the valve assemblies are completed, make one last check on the inner seating of the valve and the tightness of the valve cap by placing your finger over the hole in the valve cap and trying to close the pneumatic; very little leakage should be present. It's now time to finish stack assembly. You should have the shims glued to the trunk boards as previously mentioned, and drilled out.
The trunk boards should be trial assembled -- no glue -- using 1/4" bolts, rods or dowels in the 4 holes that were drilled for the bolts. Apply clamping pressure to top and bottom. Check to make sure the seams close well -- no gaps. (This is where a high-quality saw blade will help.) NOW, measure the distances between the decks and the overall height to make sure it matches the original. If it's okay, disassemble and glue together with hide or woodworkers glue. Don't be afraid to use too much glue (internal leaks will drive you crazy!). Holes can be drilled out when dry to remove excess glue. When drilling to remove excess glue be sure the trunk board is face-down on the table to prevent glue crumbs from getting under the pouches. Vacuum or up-end the stack to remove loose material. Excess shim material can now be removed from the trunk board. Proceed as per Reblitz instructions.
Believe it or not, the Gulbransen can be as easy to pump as the baby on the foot pedal shows! Check every step again for leaks, etc., before proceeding to the next step and you labor will be rewarded.
If you have any questions about these procedures, let us know.
Bob and Sonja Lemon
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(Message sent Fri 20 Dec 1996, 21:47:21 GMT, from time zone GMT-0800.) |
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