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MMD > Archives > March 2000 > 2000.03.06 > 10Prev  Next


Properties of Good Pneumatic Cloth
By Craig Brougher

I don't know about the cotton and rubber pneumatic cloth that "wears
out in three months."  That's a new one to me.  But there are several
things one can look for in determining which pneumatic cloth he should
test.

In the first place, the original cotton and rubber pneumatic cloth was
not intended to last much over what they called "about 50,000 plays"
in a 44-note box.  Few home instruments would ever reach this in its
lifetime of being played some every week.  But suppose you had an
instrument played by patrons about 50 times a day, 6 days a week
(that's a LOT).  That cloth then would last only 3.2 years at that
rate.

I think the original manufacturers badly underestimated the life of
their material, or just didn't want to have to replace it for supposed
wear and tear.  ($15/week in nickels, $780/year, $2496 in 3.2 years).
So whatever the rate of wear, a small box would pay for itself usually
by the end of the first year or the middle of the second year.

Double the number of notes played, and you increase the life maybe
by another year, at this rate.

Modern replacement cloth may not even come up to these very
conservative standards, however.  By increasing the percentage of
filler (clays) and by curing the resultant rubber just a little too
much, you can get a pneumatic cloth that's far too stiff.  Add to this
a cloth that's made from thread that's too large, or a weave that has
too many threads/inch, and you have a recipe for self-destruction.

I can't really tell anybody how to inspect and feel cloth to know if
it's any good.  That comes from having done it for decades, and having
run through your fingers both cloth that you know is the best, cloth
you know is the worst, and all attempts in-between.  But basically here
are the factors you must have:

1.  The cloth should have about 110-120 threads/inch.  That's half the
density of a good bed sheet.  The thread should be very very fine.

2.  It should be woven of the very finest (ideally) Egyptian long fiber
cotton in the world.  Otherwise, it should be very silky and limp.

3.  The rubber should be a bit thicker than the cloth ideally, and the
whole should not be thicker than about .007"-.008".

4.  The resultant with the spread rubber should feel limp and smooth,
and "smell like a tire store," as Art Reblitz once put it.

5.  Holding the cloth up to a bright light, you should not see but
perhaps two or three pin-holes per square foot, if anything at all
(ideally).  This won't be perfect in all batches, so don't sweat it.
It's no big deal.  (There is a vast difference between a "pin-hole" and
a small void in the coating.)

At this point, you have something that you can check out.  When you
start buying cloth, the first thing to do is buy in sample quantities.
Anything you don't like, keep for jobs like sealing and spotting over
screw access holes and stuff like that.  The hot hide glue is put on
the patch itself, so once it's dry the patch will hold air like a
cartridge.

The additives the formulator adds to his natural gum latex is what
causes the latex to last.  That's called "plasticizer."  I don't know
what it is, except that most plasticizers, at least for plastics, are
heavy-bodied oil of some kind.  He will also add, I suspect, some
activated carbon to prevent oxidation during the heat cure and even
later on.

Improperly cured rubber coatings are coatings that either stay in the
oven too long or not quite long enough.  There is absolutely no way to
know this by feeling or inspecting the finished cloth, because by now
it has talc on it.  But the comments that some cloth only lasted a few
months under normal playing conditions is too bizarre for me to even
accept at face value, because I don't know how anybody could make that
bad a product, even on purpose.

The tiny little "pin holes" you may see at the cloth peaks of a
pneumatic after a few weeks, by the way, is normal and does not
fall under the heading of "defective cloth."  Because of the extreme
stretching at these points, the rubber wears right off when the
pneumatic closes too far.  But that won't hurt your pneumatic.  It will
still test just as tight as ever.  However, these little tiny spots
actually help by "strain relieving" the rubber so that it isn't pulling
laterally along the crease any more.

When you buy cotton and rubber pneumatic cloth you are buying a
product in which you are entirely at the mercy of the formulator who
coats it.  There is absolutely no recourse back to him at all, because
he doesn't make enough of it to be forced to compete.  You take his word
for it.  "Yo' pays yo' money an' yo' takes yo' chances!"

Regarding felt bumpers inside the pneumatics -- that is not necessary
whenever you have an upstop rail on a player.  The pneumatic gets its
full power closing from fully open cloth, to about half closed.  But if
the cloth is allowed to be clamped too tightly between the pneumatics
leaves, then it will wear out quickly.  That also means, if your
pneumatics start from a half-closed position to an "almost closed
position," then it will wear much faster.

What tears up cloth in normal play is from being bent rapidly back and
forth.  If you go from no crease to half crease, it will take longer
than if you bend it deeply to start and then work back and forth
rapidly.  The outside layer of rubber must stretch more and compress
more, and the heat does it in.  When the cloth starts open, half the
closure is taking place on rather flat-sided cloth whose movement has
distributed the bending across the surface, rather than concentrating
it all in a sharp fold.

If you don't wish to take a chance with modern cotton and rubber but
still demand a "natural covering" on all your pneumatics, I suggest
some extra thin cabretta covers with double cloth hinge backs.  That
is the best there is, but it's very expensive stuff.  Even then, are
there pinholes, overly thin places, or inconsistencies in thickness
that would give each pneumatic a different characteristic?  You might
just have to take the goat's word for it, and I promise you, if
something's wrong later on, he will definitely give you your money back
or a dozen replacement hides.  But you can always complain to us here
on MMD -- We understand.

Craig Brougher


(Message sent Tue 7 Mar 2000, 02:52:49 GMT, from time zone GMT-0600.)

Key Words in Subject:  Cloth, Good, Pneumatic, Properties

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