Re: Frozen Gulbransen, anyone?
By John Grant
Hello Doug Rhodes (and listreaders),
Well, guess I'll have to jump into the Gulbransen frey:
> Date: Fri, 2 Feb 96 16:21 PST
> From: drhodes@IslandNet.com (Douglas K. Rhodes)
> To: automatic-music@foxtail.com
>
> Subject: Frozen Gulbransen, anyone?
>
> The suggestion about putting the Gulbransen stack into a freezer
> overnight and then jumping on it (or smacking it in just the
> right spot) may not be so far-fetched. I have a friend who quite
> successfully dismantled a Duo-Art expression box with precisely
> that method, as per instructions in an old AMICA Technicalities
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> bulletin. The old hide glue gets pretty brittle at around zero
^^^^^^^^
> degrees Fahrenheit. If the piano plate is cracked, and
> Gulbransens have such an ornery reputation anyway, what have you
> got to lose?
>
> Cheers
>
> Doug Rhodes
[Mounting soapbox and preparing to blow own horn.]
The "kinetic" method of opening the Duo-Art expression box is something I developed in the mid 70's, demonstrated at the 1979 Philadelphia AMICA convention, and then documented in the December 1979 AMICA Bulletin, page 214. I have used a similar but slightly different method on Gully glued stacks (GGS). The method is also similar to the freezer/valley/step method described previously in these spaces (sorry, I didn't keep the reference.) which, like the expression box method, makes use of a tensile fracture of the glue joint. The method described below utilizes a shear fracture. Similarly, freezing is recommended. (Minnesotians will have no difficulty with this part at this time of year.
But before doing anything, drill 6 or 8 evenly spaced 1/8" holes through the width of the pneumatic decks (parallel to the long dimension of the pneumatics) stopping when you are about 1/4" into the main chest. You may need an extra long "bellhangers" bit for this. (These will mark the locations for screws to remount the decks after rebuilding, further described below.)
Identify a firm surface having a rigid step with a height slightly less than the thickness of the Gully main chest. Something like a sidewalk with a concrete step will do. Place one ond of the chest so that it rests against the vertical edge of the step. If the step is higher than the chest thickness, shim the chest upward with scrap lumber until the glue line between the chest and the pneumatic decks is above the top of the step. Place a block of hardwood so that it contacts the opposite end of ONE of the pneumatic decks and NOTHING else, grain parallel to the length of the deck. Now, (faith in the methodology is IMPORTANT here) use a HEAVY (12-16 pound) sledge hammer to strike a FORCEFUL blow to the hardwood block, against the deck end, toward the step. Barring major bad luck (or poor aim), the deck glue joint will shear sideways with minimal transfer of wood from deck to chest. Rebuild normally.
The key to simplified future maintenance is this: DO NOT GLUE THE STACK BACK TOGETHER AGAIN! This may seem obvious, but many may not realize that this is not necessary and will only complicate your future if you do it. The holes that you drilled (above) can now be enlarged to allow long wood screws to reattach the decks to the chest. If you like, you can use long threaded studs with nuts on the outside of the decks (similar to the method used in the Ampico B stack). You should use a thin sponge neoprene gasket between the decks and the chest. This will compress to essentially zero thickness under the force of the screws, giving the required pneumatic isolation while not changing any stack dimensions.
[Demounting soapbox and returning to lurkdom.] |
(Message sent Sat 3 Feb 1996, 21:47:31 GMT, from time zone GMT-0800.) |
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