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MMD > Archives > October 2014 > 2014.10.02 > 07Prev  Next

Angled Edges in Large Bellows
By John A. Tuttle

Hi All,  A customer wrote to me about recovering a large reservoir
bellows and said, "I looked at the end of this bellows and did not
find any anglulation.  Is there supposed to be some?  If not, as
I tested it, the cloth is not glued on all the surfaces.  Is this
normal not to have an angle?  When you make a "work horse" if you
don't cut the legs at an angle, only a small portion of the leg
touches the floor."

I had to admit to him that this is one of those things we deal with
all the time in player pianos.  In fact, the more I thought about it,
the more I realized how much of a problem the 'squared' ends actually
'create'.  Think about it.  If the ends were angled (like a good saw
horse), there would be no need to 'rock' the bellows when gluing the
cloth to the open end of the bellow.  All you'd have to do is apply
the glue to the wood (or cloth) and set the bellows in place.  Done!

Next, and even more importantly, there's step two, when the cloth has
to make the 90-degree turn at the corner.  As we all know, since the
cloth is not laying flat on the bottom (it's actually curved because
it's two points of a circle), forcing it to lay flat on the side
creates a 'gap' at the corner.  Naturally, there are ways to 'solve'
that problem -- like stretching the cloth slightly or using tacks at
the corners, but still, it's the square bottom that's causing the

While I've always spent those extra few moments (or minutes) insuring
that the corners are well 'sealed', this evening I thought, "How hard
would it really be to cut the bottom at the correct angle and completely
avoid the 'problems'?"  So, even though I'm no math wiz, I found that
determining the correct angle for the bottom is actually quite easy if
you have a protractor.  Simply measure the angle when the bellows is
fully open to its correct span and divide by two.  Then offset the
angle of the saw blade by that amount and trim off the excess wood.
The span of the bellows remains the same.

Any thoughts?

John A Tuttle
Brick, New Jersey, USA

(Message sent Thu 2 Oct 2014, 03:06:00 GMT, from time zone GMT-0700.)

Key Words in Subject:  Angled, Bellows, Edges, Large

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