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MMD > Archives > June 2005 > 2005.06.29 > 04Prev  Next


Adjusting Music Roll Spool Friction Brakes
By John A. Tuttle

Hi All,  Even though I've worked on literally thousands of player
pianos and read every service manual I could get my hands on, I have
never yet come up with or read an accurately descriptive explanation
of how to adjust the forward roll or rewind friction brakes.

The question is: How Tight Is Just Right?

One would think that this should be a measurable amount of drag.  And,
if so, simply attaching a spring scale (like a fish scale) to the end
tab and pulling on the roll would render a certain figure.  However, if
such a figure exists, I've never seen it.  So, I adjust it by "feel".

How does one explain "feel"? Regardless of which words are used, they
are all subjective.  "Light", "Medium", "Firm", "Slight", and "Heavy"
mean different things to each person.

The problem with adjusting the forward roll friction brake by feel is
the effect it has on the air motor.  The amount of drag presented by
the forward roll friction brake has a direct effect on speed of the
motor.  It also has a direct effect on the longevity of the bellows
cloth, the felt bearings, and (to a slight degree) wear on the chain
and the transmission.  Point in fact, the tempo adjustment, air-motor
governor adjustment and forward roll brake adjustment are interactive.
Change any of the three and it has an effect on the other two.  This
is one fact that I have never read about in any service manual or book.

One has to wonder how the forward roll friction brake was adjusted at
the factory when the mechanism was assembled.  Most friction brakes are
extremely simple devices consisting of a block of wood, a piece of felt,
and a flat piece of spring steel.  Adjusting the tension is usually
accomplished by bending the tab (where the spring mounts to the block)
one way or the other.

Other brakes systems employ a bolt and a lock nut which allows the
tension (or drag) to be adjusted across a wide range of settings from
minimal to excessive.  Still others employ a relatively long coil
spring that is adjusted by stretching the spring to a certain tension
and then sticking a small nail through a hole in a block of wood
through which the spring passes.

The point is, in virtually every instance, the manufacturer provided
some way to adjust the forward roll brake and rewind brake.  And, that
being the case, it seems to me that every manufacture was remiss in
providing detailed information about how to correctly adjust the
brakes.

At this late date, can a correct figure for 'drag' be determined? In
this forum, could we arrive at an acceptable average through
experimentation?

My Lauter-Humana is one of those systems that employs a bolt and a
lock nut.  I have never changed that adjustment.  However, its accuracy
is dependent of the thickness of the felt piece between the spring and
the brake drum, and I have changed the felt (which was contaminated
with oil and showed signs of wear).  Naturally, I tried to replace the
felt piece with one that seemed identical to the original piece, but
would a few thousandths of an inch in one direction or another make
a difference?  I think so...

My Ampico has two different types of brakes.  The forward roll brake
consists of a block of wood with a felt pad, a coil spring, and a
regulating screw (like those used to regulate let-off), and it is
adjustable via a leather nut on the regulating screw.  The rewind
brake is nothing more than a piece of (what looks like) piano wire
with a regulating button attached to the end.  It's connected to the
Play/Rewind lever such that when the transmission is in the Rewind
position, the button makes contact with a pot metal disk that's
attached via a rod to the take-up spool.  However, both are obviously
adjustable!

I suppose the bottom line question is, Does it really make that much
of a difference as long as it works?

Obviously, there are those who have experienced problems which can
be directly attributed to a faulty or maladjusted friction brake.
And, as was explained earlier in this posting, the friction brake is
an interactive adjustment.  At this point in time, and in the absence
of factual data, I will continue to adjust the brakes by "feel".

My approach for many years has been to adjust the brake so that the
roll doesn't billow.  However, I will try to remember to carry a spring
scale with me and measure the drag on various players.  Hopefully, over
time, I will collect enough data to arrive at some reasonable
conclusion concerning 'How Tight Is Just Right'.

Musically,
John A Tuttle
Player-Care.com 
Brick, New Jersey, USA

(Portions of this posting will be used in a new web page at Player-Care
about "Adjusting the Brakes".)


(Message sent Wed 29 Jun 2005, 13:03:21 GMT, from time zone GMT-0400.)

Key Words in Subject:  Adjusting, Brakes, Friction, Music, Roll, Spool

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