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MMD > Archives > July 2002 > 2002.07.27 > 03Prev  Next


Adjusting The Pneumatic Finger Tracker System
By Craig Brougher

Rolls that tear on rewind are caused by a multitude of things, and
seldom the geometry of the spool box or its components.  I do not
recommend modifying the spool box because you are tearing rolls.
I also do not recommend taking off the rewind brake -- on any but the
worst players with the worst tracking mechanisms.  And I definitely
do not recommend shortening the takeup spool!

The takeup spool powers the roll through during play, which means all
the longitudinal (lengthwise) force exerted is at the takeup and the
sideways force of a [crooked?] wind isn't enough to overpower that
friction and force.  So shortening it will prevent wandering of the
roll paying up on it but will tear the roll itself on its own flanges,
and if not directly tear it, it will stretch the edges of the roll and
curl them, making them impossible to play again.

So far, all we're heard to do is to modify the original mechanism.
I'm going to show that isn't usually necessary.  The first thing to do
is to rebuild the tracker system and regulate it such that it tracks
well.

We will assume that your player has a pair of tracking fingers and that
it is an air tracker.  In this setup, the important finger is the one
on the left.  Your player would actually play most rolls well with only
this finger operating, if you regulated it correctly.  We are also
assuming that the tracking mechanism is airtight, both sides.  The way
you check the airtightness is this:

1.  Remove a tube off the tracking bellows and suck very lightly on the
finger pad pallet.  If it is airtight, then put a test tube on the
bellows nipple and suck on it.  If you suspect a leak, blow on it and
see if you can feel air or hear it escaping.  Fix it first.

2.  Next thing is, Disconnect the linkage to the roll chuck and watch
the double bellows.  Does it favor one side or the other -- without the
spring?  Do the covers get taut when one side or the other is opened?
Does it move back and forth easily, without much effort? Or do you have
to push a little? Fix it.

3.  Do the tracking fingers open with almost no pressure, and do they
close smartly, with no friction? Test it with a 3/8" wide strip of a
3"-long Post-It note.  Each finger should easily open.  If one or the
other seems harder, and bends the paper more, even them up first.

Now reconnect everything loosely.

4.  Get a couple of leather nuts and jam them down between the leaves
of the tracker bellows in order to evenly space them.  Now if the roll
chuck is operated by a cam arrangement at the transmission, set the cam
to the exact center of it's travel when the bellows are centered
perfectly, and tighten the linkage.

5.  Also, check all linkage guides, that they are solid and do not move
or even budge, and that their bushings are smooth and snug and will not
allow that rod to move sideways or flex.

6.  Now remove the leather nuts and operate the bellows back and forth
to check your adjustment.  If you are too much left or right, do it
again and keep adjusting maximum travel until the tracker is centered.
Tighten things up now and leave it.  Don't mess with that any more!
If you have a problem, it will not be that, and don't goof it up.
If you've done it right, that part will be just fine and the only
problem left will be the setting of the tracking fingers to the roll,
or an off-center takeup spool, or both.

7.  Begin with a new roll, new roll paper, from someone who cuts a
perfect roll, like the Tonnesens or Dave Saul, or Rob DeLand, or any
other roll you know you can trust.  But it has to be brand new, with
good clean holes, preferably full size holes, like a Keystone Roll (or
original Ampico roll).  Disconnect the air motor chain so you can drive
the takeup by hand.  Swing the right hand finger out of the roll path
or clamp its tube so it won't work (preferable).

8.  Adjust the left finger to just touch when the bass note trackerbar
holes (not sustain pedal hole) are perfectly under the holes in the
note sheet.  A full sized hole should be aligned so that its left edge
is even with the left edge of the trackerbar hole.  Be careful about
this.  Ignore all holes to the right of the first 30 note holes.
That's paper expansion or shrinkage.  All tracking is done on the left
side of the note sheet first.

9.  Spin the takeup spool and check alignment.  Let the vacuum move the
roll to the right, as the roll drifts left.  Now make any corrections
you need to make, using just one tracking finger on a new roll.  If
that new roll tends to drift right, get another one.  No all rolls are
good rolls.  The left chuck spring is your return to the right.  It
exerts a slow restoring force and is the tracking centering device.
The right bellows (if a vertical unit) will drive the roll to the
right.  So you want, you can disconnect the right bellows from its
finger and sub in a #70 bleed in a stub line from the bellows nipple.
That weakens the right restoring force but doesn't remove it.

As you watch one finger controlling the roll path, make sure the paper
never goes beyond the line you've set.  It cannot go further left than
what you want it to go.

10.  Now add in the right finger.  The right finger is set when the
left finger is contacted but not quite activated.  Put about a paper's
width distance between the right roll's edge and the right finger to
start with.  Test this out thoroughly.

11.  Now hook up the air motor, and start testing wide and narrow paper
on it.  If you have done this right, you will only adjust your right
tracking finger.  You will not adjust the left one.

12.  If the roll tends to crowd the left or right flange on reroll,
that means that your bellows tracker is still not centered pneumatically.
It doesn't mean that the tracking fingers are wrong, but the bellows
didn't center where you thought they should.  All tracking units are
supposed to center themselves on reroll.  So go back and see where it
tends to naturally rest during reroll, put your leather jam nuts in
that bellows while it is rerolling, without moving the leaves, and
readjust the center position to that position.  Leave the fingers where
they are.  Notice, we are working back and forth, and no particular
adjustment is inviolable.  You may not even be able to see yourself
making a change, but it will change.

This is only one way of adjusting them.  It isn't the only way, and
I use a half-dozen ways to do it, but this is what I do for a living.
I am telling those who do it only occasionally how they might attack
the problem.  For instance, I never disable the right finger, but it's
best to know that the left finger is the control finger.  Please do not
put your takeup spool on the lathe and modify it just to get rid of a
problem that may be due to a poorly adjusted tracking system.

One last comment is that about the rolls themselves.  Some rolls will
not track, and if they have been beat up by a bad tracking unit, they
are basically ruined, until you "fix" them.  However, it's good
practice to take old rolls with slightly feathered edges and see how
your restored player will play them.  And it isn't necessarily wrong to
take off the reroll brake.  As long as the takeup spool doesn't
freewheel very easily, it will be okay.

The problem is with long rolls.  A loosely wound large roll can be a
real mess, and you're likely to tear it yourself when it's loosely
wound.  My suggestion is to adjust the reroll brake, rather than remove
it.  It is only lucky that so many old players have stiff grease in all
the "goes-arounders."

Craig Brougher


(Message sent Sat 27 Jul 2002, 16:47:13 GMT, from time zone GMT-0700.)

Key Words in Subject:  Adjusting, Finger, Pneumatic, System, Tracker

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