If any are considering building a jig to adjust the travel of Duo-Art
accordion pneumatics, I would suggest that they design something that
will ignore the natural tipping of the sections as they clamp together,
and allow one to readily make small adjustments in the section travel
as they watch an accordion stack travel pointer in action. This makes
such a device useful and accurate.
So, for instance, you would not want to attach a pointer to one of the
end sections as they cascaded because the pointer would tip until every
section was machine shop square -- and with wood and felt that isn't
possible or necessary. Factory adjustment did not require parallel
sections, only overall movement as measured at the center of the top
For instance, if the jig has solid wood enclosed sides, it might not
be the most convenient device you ever thought up, unless you wanted
something to remind you how time-consuming and difficult perfect
parallelism and displacement of 12 compounding, interacting adjustments
can actually be. You will never forget the experience, I suspect.
As far as designing something with a little pointer on it -- that's not
a bad idea, but I suggest letting the pointer ride up and down on the
top section of the accordion stack, after the accordions are mounted
on the expression box. You'd be surprised the errors that creep in to
your accordion travel, simply by first mounting them in their positions
and then attaching them to the lever. So here is a quick way to do
this operation and get them exactly right:
To make a very simple height gauge which is unaffected by the tipping
of the section boards and as accurate as need be, cut a 4" long block
of wood roughly 1-1/4" square. Since you will need to screw it down
to the expression box top, recess the back of that little block to be
a quarter inch thick and cut a slot in the end of it so you can unscrew
one of the top screws and simply attach it by sliding it under the
screw head and tightening it back down again.
Since the slot allows adjustment, you will be able to rotate and slide
the block a little to align its "cursor" with the center of each
accordion. By centering the cursor, you don't have to worry about
getting perfectly parallel boards all the way down the line.
The cursor is just a 6-8" long piece of brass model tubing, say 5/16"
diameter, guided by another piece of next-size-up model tubing pressed
through the other end of the block, centered perhaps 5/16" from the
end. They are telescope-fit tubing and very accurate, when the cursor
tube is riding on the top of the accordion.
Now you screw down an accurate 6" scale to the end of that block,
pointing up in the air. Then to the brass tube cursor you wind about
5 coils of a little spring (if you don't happen to already have one)
that will hold whatever position you initially adjust it to and slip
that over the cursor, above the block, so that its wire pointer can be
sprung out and bent in to point against the ruler.
Talk about accurate! This determines where you start, so just slide
your pointer up to an even number to start on! From that point, you
can take it and your travel gauge will be absolutely correct.
Now the irony of all this is that the exact accordion travel is
only a convenient place to start from, if in fact what you want is
"perfection." By the time the box is correctly regulated on the bench
with a fairly high pressure, well-regulated vacuum supply, you will
have changed every setting slightly from "perfect."
You might be surprised what a difference it makes, once you realize
that these settings multiply, or cascade, and that tiny errors of 1/32"
or less can easily make 3-5" of difference at higher intensities,
changing linearity. But to do that you need a rather extensive setup
arrangement just for Duo-Art boxes. Still, that's how you begin.
With many if not most, that's sufficient, and with weeks or months
of diddling, listening to rolls, you can finally get the expression
about right that way, too.