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MMD > Archives > January 2001 > 2001.01.25 > 08Prev  Next


Cutting Compliant Pneumatic Cloth
By John A. Tuttle

Hi All,  I just realized that I've been doing something for so long
that I momentarily forgot why I do it, or where I might have learned
the 'rule'!

I'll get to the point.  All weights of bellows cloth will rip in a
straight line in only one direction; lengthwise.  If you attempt to
rip it across its width, it comes apart horribly.  Also, bellows cloth
doesn't stretch much across its width, but it will stretch down its
length.  (I'm certain it has something to do with the manufacturing
technique.)

At sometime early in my career as a player rebuilder, I vaguely recall
hearing, reading or being told that all bellows had be made such that
the "span determines the width, and the perimeter, plus overlap,
determines the length".  At the time, it must have made good sense
(since the cloth was most easily ripped lengthwise), so I never had
reason to question the matter further.

As the years passed, I forgot 'why' the 'rule' existed because it was
so much easier to rip the cloth than it was to cut long straight lines.
However, when I started selling bellows cloth, it began to bother me
when people ordered lengths of cloth that couldn't possibly reach all
the way around the perimeter of the bellow they intended to recover!
Only thing is, I couldn't put my finger on 'why' it bothered me.....

As I have stated before, selling cloth by the running foot instead of
in custom-cut strips will typically leave the customer with lots of
excess cloth!  Selling the cloth in custom-cut strips leaves the seller
with cloth that can no longer be sold by the running foot.  This
conundrum seems to have no 'Happy Answer' -- IF you forget the basic
'rule'.

Now, I had to examine the 'rule'.  Why was it imperative that I only
sell lengths of cloth that span the perimeter (plus the overlap) when
the cloth is wide enough to do the job?  It was obvious to me that it
no longer just a matter of my personal convenience.  I had to have a
legitimate reason -- after all, bellows cloth isn't cheap!

Then it hit me: Springs stretch!  You can't place the stretchy part
of the cloth across the span of a spring-loaded bellow.  Almost
immediately it will begin stretching and the air-tight layer will begin
to weaken.  (I can hear those who are saying, "Put a strap across the
span and you won't have to worry about it.)  True, you could put a
strap or two across the span, but is it my responsibility to give a
complete set of 'special instructions' to those people who may not
understand the ramifications of their intended actions?

Well, you can see that I remembered the 'what' and the 'why'.  I still
can't remember the 'who', 'where' or 'when', but that's not really
important.  Now the question is, 'What to do now that I remember?'

Any ideas?

Musically,

John A. Tuttle


(Message sent Fri 26 Jan 2001, 00:06:24 GMT, from time zone GMT-0500.)

Key Words in Subject:  Cloth, Compliant, Cutting, Pneumatic

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