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Adjusting the Forward Roll and Rewind Brakes
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/Rewing 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 poorly adjusted 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 in either the Forward Roll (or Play) mode or Rewind (or Reroll) mode. This can be accomplished by simply observing the roll as it is playing and rewinding, and then adjusting the brakes accordingly. 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'.
John A Tuttle
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