Materials Spotlight + Method: Gaskets

Gaskets keep everything nice and tight. They keep the suction in where you want it, and the atmosphere out. Since all valve boxes are made of blocks of wood, and even well-mated wood surfaces are not airtight, there must be a membrane of some sort which is suitably compressible, but also durable.

The traditional candidate is split leather. When leather of proper quality and consistency is used, it does both jobs well, and leather to wood with hot hide glue is a match made in heaven. There simply isn’t a better way to work other than the original way.

However, there are alternatives.
When I say alternatives, I want to stress I am not taking about the adhesive part! For my opinion on glues, see previous post here.

I was speaking of a “modern” gasket material of neoprene. Plastics get a bad rap in the piano industry sometimes, because in the beginning, the technology was inferior and the product didn’t age well (plastics were introduced into pianos as early as the 1930’s). However, plastic materials have come a long way, and like every product there is a range of quality.

Traditionalists will turn up their noses at this idea, but that’s fine. Tradition has its place, and I respect it where I feel appropriate, but this doesn’t prevent me from trying new things.
In the case of neoprene, for a material that was modestly cheaper, easier to source, slightly easier to work with and – most importantly!– well-performing as leather, that seemed good enough for me. Time will tell!

My main concern with this type of product in the long term would be elasticity (being permanently compressed and not expanding in drier weather), and structural integrity (starting to disintegrate over time). On the question of integrity, since a gasket is –by definition– always sandwiched firmly between two pieces of wood, the oxidization problems should be minimal.

The material comes in sheets and you just cut what you need, in the most efficient way you can manage. For cutting straight lines I use a steel rule and a rotary cutter, on a cutting board designed for the cutter (“self-healing”).

For punching holes I use a handheld punch, which works well for screw holes (the most common kind). For anything larger than that, you really need a punch set to do a neat professional job.
For small and medium surfaces mark all holes on a given side with chalk (lightly) and then dry fit the gasket to the surface. The perimeter outline can be rough at this point, doesn’t need to be perfect now. Release the piece and place the gasket on a punching board. The cutting board worked for me for this material, because it’s so light, you just press it out by hand.  I would not have used a hammer to drive the punch on my nice cutting board!
Then do the screw holes, however you want. When all done check against the piece, and assuming it’s good, go ahead and glue it on real good (the neoprene I use has two different sides, it’s the “skin” side which gets glued down).
Finally cut away the perimeter edge with a pair of shears or long scissors. Easy!

The only thing to watch for is that the thickness tolerance is kept faithful, when you replace gaskets. If you are putting neoprene in place of a gasket that was originally designed to be leather or blotter paper, the compressibility will not be identical, so this is something to keep in mind. If you are not duplicating the original in terms of material, you should still attempt to match it in terms of dimensions, wherever possible.
Gaskets can be made from any number of things, but traditionally it has been leathers, cork, blotter paper or other cardboard type papers. You can choose to use any number of solutions, but don’t use the wrong material for the wrong reasons.
The thing about quality leather is that it is getting harder to source. It’s just another one of those commodities that has become more scarce, for several reasons. That was part of my decision to go with neoprene.
But using cheap and inappropriate materials only to save a few nickels and a few minutes is false economy. Spare a thought for the person who will have to do the next restoration, it may even be you! Trying to scrape off disintegrated plastics mixed with modern glues is truly drudgery of the worst kind. Don’t let it be you!

No photos this time, but I will illustrate gasket use in the following post!

Tracking Device: Rebuilding and Testing

This is going to be a lot shorter than the preceding post, for a couple of reasons.

Firstly, half the battle with a component like the tracking device is simply understanding how it operates. You can’t do proper rebuilding and testing/troubleshooting without this knowledge.
It took me a few days of fairly steady thinking on this topic, for it to start to sink in.

The other thing is that there is not a lot new here, in terms of components. I’ve covered pneumatics, I’m probably not doing pouches (however this is covered extensively in the Reblitz book), and I will specifically cover gaskets (simple) and valves in future posts.

Like the other components, good sealing is a must for proper function. This means the internal channels, the recovered bellows, the mating of the primary valve facings to the box, and good gaskets.

Once all this is done, it’s a matter of reassembly and testing. Here’s what it looks like back together:

Tracking device, nearing completion

And so let’s make sure it does what it needs to do.

First get a suction supply going, to test. In a perfect world you have a test pump from an old reproducing piano, but barring that, a regular shop vac will suffice (it’s what I used). Just regulate the suction so that you are in the 5″ water range (a vacuum dial gauge is good for this, or a home made water vacuum gauge). I made a laughably cheezy regulator, with a clothes pin and some elastics, to hold a piece of tubing a little bit outside the mouth of the vacuum. MacGuyver would be proud!

The drawback to testing with a vacuum is the noise. Apart from being generally grating, it also makes it difficult to hear leaks when troubleshooting. But, we must use whatever tools at our disposal.

Hook up the suction supply to the appropriate nipple on the box (it should be the one that is not otherwise identified). Then run the following series of tests:

1) Close off all 4 inputs (you don’t need to tube to an actual tracker bar to do this). Is the system balanced? You should see the pneumatic cloth get sucked in slightly in the bellows, but other than that, they should stay pretty much where they are. More on that in a moment. Assuming all good, continue.

2) Open the outer holes. Still balanced? Good!

3) Open the inner holes too, all holes open. Still balanced? Okay!

These tests check the balance of the pneumatics, if the bellows list to one side or another, or if they are otherwise not behaving identically to each other, we have a problem! The problem is a leak somewhere, so you’ll have to track it down and fix it. Do it now, show no mercy to leaks whatsoever. It will not ever work if it leaks, so if it means taking everything apart and checking each component separately, just do what it takes!

Once we have established balance in equilibrium, let’s check it in disequilibrium.

4) Close all holes again, then open just one outer hole. The bellows should track accordingly, moving smoothly in concert to one side. When you cover the hole, they should return to default halfway position. If they move quickly but don’t return reasonably quickly, this is a troubleshooting tip, likely a blocked bleed. Try the other outside hole in the same manner.

5) Same as step 4, but concentrate this time on only opening each outer hole (not at same time) just a little – halfway or less. The bellows should still react and begin to shift as soon as the hole is opened partially.

6) Cover only the inner holes, and repeat steps 4 and 5, one inner hole at a time. The bellows should again perform the same way.

Assuming it does all these things well, you should be good. But if there is something which makes you squirrelly happening now, just check again and again, repairing if necessary, until it looks like it should.

One thing I noticed on my first attempts, was that the right pneumatic would noticeable jerk when getting suction signal. It is a quirk of the design that the pneumatic is only mounted on the shift box with a single screw. This is not ideal from a “no motion” perspective, so I had to dismount it (which ruined my gasket, it had to be cleaned off and replaced), then check for flatness, and then make sure the pneumatic sits perfectly straight on the box, supported equally on both top and bottom, when you glue (or shellac) the gasket back on.

Thankfully the pneumatic had an access port for the screw, so I was just able to open that up to pop off the pneumatic, I didn’t have to ruin the the recovery job I had done.

This does remind me however, that there are possibilities for some real bouts of tedium and frustration when troubleshooting. What’s more is that the closer you get to the end, the chances of time-wasting increase, unless you take the time to really check your work at every stage. I must repeat this mantra to myself constantly!

Here’s a video of a testing session I did:

So, that’s basically it! Just reattach whatever mounting blocks or other hardware to the unit, and set it aside until whole action reassembly.

On to the next thing!

Actually, let’s take a quick side tour to gaskets….TBC

Tracking Device: Theory and Design

Although not as eye-catching as the motor, the auto tracking device is just as necessary and just as sexy. In fact the tracking device is usually the most mechanically elegant feature of the whole dang piano! In his introduction to the Standard Tracking Device (p 143), Art Reblitz calls the Standard in particular “one of the most sophisticated pneumatic mechanisms in any piano”.

The tracker in my piano is very nearly the same as a Standard, it operates on exactly the same design principles, especially in the valve box (also called shifter box). However in terms of appearance and layout, it is essentially an Autopiano tracker (see image below). Indicators are the bottom bleed chamber, as well as the vertical orientation of the pneumatics, plus another particular feature I will mention later on.

Note that while the general principles of the following information apply widely to most “automatic” pneumatic trackers, there are specific differences which may apply.

Autopiano tracking device

The tracking device keeps the paper rolling on the “straight and narrow”. This is vitally important, because if the paper becomes misaligned with the tracker bar as it unspools, the music becomes real bad, real fast. If we continue with an automotive analogy, the motor and the transmission are self-explanatory. The tracker can be considered the steering wheel. Imagine therefore, trying to drive your car, and the wheels did not follow what you were doing as you turned the steering wheel: it would be interesting, but not in a good way!

And so, let’s dig in a little bit and try and figure out how this thing works. I admit it has taken me some time to understand this thing. There is an awful lot to digest here, so understandably it may take you a while to get through it. Alternately you can watch a video by John Tuttle here. In fact, I recommend that you read all this, then watch the video, then do it all again!

Once it’s all taken apart, we see that it consists of two outside (primary) valves, six pouches and seven channels – three of which are almost too small to be considered true channels.
The 2 primary valves are paired with a set of primary pouches. There are two “wannabe” inside valves paired with what are called the “cutout” pouches. These are essentially two thick wooden discs (which look like primary valve caps) glued on top of the cutout pouches. Over head of the of the cutout pouches there are two slightly larger pouches, cleverly called “overhead” pouches. The overhead pouch has the power to override the cutout pouch, due to larger surface area (in my case 1 1/8 vs 7/8 diameter).For channels, we’ve got 4 “inputs”, which is where the four nipples on top of the valve box are tubed directly to the 4 specified holes in the tracker bar. Inputs 1 and 2 both lead to a matched but independent channel which runs underneath both the cutout pouch and the primary pouch. Inputs 3 and 4 are essentially direct feeds to each overhead pouch well (again, independent of each other).On the underside of the valve box (on my model, at least) there is a suction supply, which is just a small hole in the valve well with a nipple outside to hold the tube.Finally, there are two interior channels connecting the primary valves to the pneumatics. The primary valves determine if the pneumatics get suction or atmosphere, so these can be considered the “outputs” of the valve box.

Confused yet? I can’t blame you, after having read all that!A picture is worth a thousand words, so here is what the inside of the valve box looks like:

Inside of tracker valve box

The first thing that will help simplify matters is to notice that the valve box is a stereo set. In other words, you really only have to understand “half” of what is happening, and the other half does the same thing.
The second thing is that even though the 4 inputs from the tracker bar can theoretically give up to 16 different permutations, for practical purposes it’s actually less than that.
If we work backwards and follow the path, we can see that the tracker linkage (which controls the position of the music roll, via the spool cam) is effected by the movement of the tracker pneumatic. The tracker pneumatic moves (e.g. opens or closes) depending on what “signal” (suction or atmosphere) it is getting from the output of the valve box. This signal is switched on or off by the primary valve. The valve is controlled by the primary pouch. The primary pouch is arranged inline with the cutout pouch, and both of these pouches are fed by the exterior hole of the tracker bar hole set (inputs 1 or 2, as labeled by me). The overhead pouches are fed by the interior holes of the tracker bar, which are again labeled 3 and 4 respectively on my box.

Diagram showing how tubing maps from tracker bar to shifter box

States of play, of one side of valve box (meaning one valve only):
1) Both (inner and outer) holes of tracker bar are open (no roll paper is covering). The inner hole triggers the overhead pouch, which overpowers the cutout pouch. Even though the outer hole is open, the cutout pouch is overpowered, so the valve is not opened, and the suction goes through to the pneumatic.
2) Both (inner and outer) holes are closed. The overhead pouch is not triggered, but it doesn’t matter because neither is the cutout or the primary pouch. Again, the valve stays down (closed), and the pneumatic keeps receiving suction.
3) Inner hole closed, outer hole open. The overhead pouch is not triggered; the outer hole allows air to pass to the primary pouch and lift the valve. The valve opens, closing the suction chamber and letting atmosphere into the pneumatic. This is what could be considered “default” setting
4) Outer hole closed, inner open. Unless the roll was damaged in a very particular way, this situation would never occur. In theory it would mean that suction continues to that pneumatic, as in case 1.
Note that for the first 3 scenarios, as long as the same thing is happening on both sides of the tracker bar (and valve box), the system can be considered balanced, which means the pneumatics are acting equally in concert, and not trying to move the piano roll left or right to compensate.
When there are differences between the sides, we will have an unbalanced system, so we have to revisit our scenarios.
5) One inner hole closed (on one side), other three holes open: atmosphere is fed to the open holes, for practical purposes it is the uncovered inner hole that leads to the overhead pouch, which will expand and let atmosphere pass to one pneumatic. The other pneumatic will still be getting suction, so it will pull the atmosphere pneumatic back into balance.
6) One outer hole opened, other three closed: the outer hole will allow atmosphere into its channel and open the valve, allowing atmosphere into one pneumatic. Again, the system will automatically rebalance.
7) One pair of inner/outer holes opened, other pair (on other side) closed: this would be an unusual situation, most likely resulting from a damaged roll. As explained by John Tuttle here, if both holes on one side are temporarily opened, the tracker does not try to correct, but just keeps status quo. Whether this was a planned design outcome, or just happy accident, I don’t know!

If that is not sufficiently confusing, another key fact is that the inner/outer holes are cross connected to the valve box inputs, so that the inner and outer hole from the same side of the tracker bar are not inline on the same input channel. Why? Because that’s the way it was designed, and that’s the only way it can work! I spent a bunch of time thinking about this, but John Tuttle gave me the above explanation, and really that’s what matters. It just is.

Other related facts:
The outer holes are for standard (or larger) sized piano rolls, standard size being 11 1/4″. The system will still work with slightly narrower rolls (i.e. the system can function using the inner holes only), but if there are rolls which are significantly wider than standard, the system is not well-equipped to respond to roll drift in this case.
Finally, the “particular feature” on my tracker is that there are no bleeds for the overhead pouches. This is related to the fact that my tracker bar scale apparently allows some air into the outer holes at all times, the holes are indexed this way on purpose. So not only is the overhead pouch larger, but due to lack of bleed it really comes down hard and fast, to override the cutout valve and keep the linked pneumatic under suction.
Furthermore, John reminded me that the self-cleaning bleeds are also self-regulating as well; the more that a valve pouch opens, the more the corresponding bleed opens as well, which means the resistance to opening increases concomitantly. Interesting stuff!
Your head probably hurts a little from having read all this, so let’s leave it there, and get into the specifics of rebuilding next time.

Sources: Player Piano Servicing and Rebuilding. A. Reblitz. Vestal Press, Lanham, MA. 1985.
“Player Piano Pointers”. Auto Pneumatic Action Company. New York, 1917. (Note: this is a public domain document, available from AMICA, with membership)