Method: Rebushing

One of the final tasks on the checklist before motor reassembly is rebushing. There are many, many bushings of different descriptions and purposes in a player piano (or a regular piano), but they are mostly variations on a theme.

A bushing is a piece of material (usually sturdy cloth) which creates a sort of “buffer zone” between a moving part and a stationary part. For example, anywhere there is a pin or rod that rotates, chances are good that there is a bushing around this part. A bushing must be the right size: too thick and it will induce unwanted friction, too thin and the moving part will not have sufficient support, causing inefficient mechanical motion and probably unpleasant noises as well.

For the present post, we are referring specifically to the bushings in the motor. You will want to redo all of these bushings, especially the ones that come into contact with the crankshaft (which is most of them). This motor has got to run a long time, so let’s freshen up those bushings and keep it tight!

Let’s start with connector arms and valve flanges. Remove the old cloth. Before we get too far ahead, you might as well clean out the bushing holes of old residue with a properly size drill bit. The fit should be snug, but don’t ream the hole any larger.

Now measure the old cloth. You will need to match the dimensions of the original bushing, the key word being original. There are two dimensions to watch for here: thickness and width.
The length of the bushing will not have changed, so when you cut a strip of cloth, the width of the cloth must match the length of the old piece. If ever the bushings are damaged or missing, you can approximate by remembering some geometry: the circumference of a circle is π x diameter. In other words, if you measure the span of the hole, multiply by 3 (and a smidge), and cut your cloth strip to this width, it should be a pretty close fit!

The thickness is tricker; measure the thickness with calipers or similar gauge, and then realize we must account for wear. Depending on wear, we may need to add ten to twenty thousands (of an inch) to replicate original cloth.

Once you’ve got something you can work with, tear a strip (good quality cloth will tear cleanly and evenly, just as well as cutting) of the proper width, as long as you need.  For bushings that go in a hole (in a block of wood), cut a bit away to make a “tip” on the strip and pull it through the hole, almost the entire way through. If you look at the cloth sitting in the hole, the two sides should touch each other, but without having the cloth bunch up in the hole. If there is a gap, your cloth is too small. If it bunches: Too big!

Then put a reasonable amount of glue (you will figure this out on your own) on the cloth and pull it the rest of the way into the hole.  Assuming you’ve used hot hide glue, let it set up for a few minutes (while you do the next, and the next), then double back before the glue hardens completely and trim the excess cloth.

There is a trick to this, and it involves a sharp instrument like a new razor blade. Nothing screams “amateur!” like sloppy bushings cut with a dull blade. To avoid dislodging your new bushing with the blade, insert a stand in mandrel (like a wooden dowel) of proper size into the bushing hole. Hopefully it goes without saying that you don’t use your crankshaft as the cutting mandrel!

For bushings which can be put in place without the above method (e.g. open cavities), you should be able to cut to size before gluing in place, as is the case with the following slide valve arm flange bushings.

Old slide valve bushings
new bushings and cloth for the slide valves

And whadya know – John Tuttle has a video on this subject too! I’ll let him offer his perspective again – click here!

There are still more kinds of bushings, such as those for the side guides of the slide valves. These will be a snap, after having done the rotary ones. They are just strips of cloth!

Slide valve guides, with bushings

Once your various bushings have all been done, collect everything (back in the correct order), and get ready to put the motor back together. Almost there!

all arms and flanges back on pianola motor crank shaft

Method: Pneumatics Recovery (hinges + cloth)

You are of course welcome to read through the entirety of the following post (I assume that’s why you’re here), but if you would prefer to watch a video tutorial on the same topic instead, then click here. I don’t plan on going into as much detail as Art Reblitz in his book (pp 52-78), but I will at least furnish a proper introduction, to give you a taste…

First, some assumptions, pertaining to teardown:

  • That the pneumatic has been carefully removed from its trunk (whether gasketed and screwed, or glued).
  • That the cloth was slit lengthwise between the bellows, and then peeled back and removed.
  • That your boards are sequentially numbered in pairs, for easy identification, on the inside face of each. (the inside board should also be marked on the exterior in a suitable place, if it happens that a particular pneumatic needs to be remounted in a particular location)
  • That the hinge was removed from both boards, and the old hinge glue lightly sanded away.
  • That any remaining cloth was scorched or smoothly sanded off, and the edges all sanded smooth.
  • That all sides are square and true, and each board is precisely the same dimensions as its mate.

Starting with these two prepped boards, we will remake a pneumatic!

Let’s begin with the hinge.

First, flashback: after having removed the original hinge (perhaps long ago), you found a source of identical but new material; likely something in the ticking or twill canvass line. It really must be 100% cotton. Having measured the old hinges, you recreate them by cutting first to length (to create a strip for a whole section). You have paid proper attention to follow the orientation of the weave, so you cut in the right direction. You then crease the hinge by folding and running a warm iron over the surface. The strips may now be cut to width to create the pneumatic hinges.

Ironing hinge material for bellows

Now, flashforward! Your pot of hot hide glue is at the ready. As are your pieces, organized and prepared. You may choose to insert a piece of wax paper in the hinge fold, to prevent gluing the hinge to itself.
Glue the end of each board where the hinge will attach. Pick up your hinge, place it on one board. Quickly take the other board and place it on top. Check positioning of the hinge (slight inset), and then clamp, with a medium spring clamp (I find large binder clips work well for this, and they are cost-effective!). Let dry, hinging is done.

Hinged pneumatic boards, waiting to be recovered

To verify the hinge, once the glue is dry gently try to wiggle the open ends to opposing sides. If there is noticeable play, you have failed. Remove the hinge and start again, until the ends travel freely and easily to open or close, but resist any sideplay.

John Tuttle has a video on this, with a slightly different perspective. Check it out here

Now, the recovery with cloth.

Again some assumptions: you have the proper bellows cloth, with appropriate thickness for bellows size, a measuring tape, you have a nice, sharp, pair of scissors, glue pot at the ready, and if necessary a jig to speed up accurate, consistent production (e.g. this)

Cut strips for your bellows, the width of which will be slightly oversize the span of the pneumatic in question.

To recover: Lay out the strip of cut cloth (inside facing up). Position the handy jig for spacing, if you have one, over top of the cloth, offset the centre. Glue first side of the pneumatic, by which I mean both edges of the left side.  Use enough glue, but not too much.

Pneumatics in process of being recovered
Detail of pneumatic recovery

Wait. Turn.  Glue end (open) edges. Wait. Turn again. Glue third side. Wait. Glue last side. Done.

This is a bit short on detail, but it is really meant as a procedural overview. There are other things to consider as well like carefully trimming the excess cloth from the finished pneumatic, to avoid knicking the cloth and wasting your work. Refer to Reblitz’s book or John Tuttle’s video tutorial for more in-depth information.

On to rebushing!


Motor, Part Two (polishing, lapping, sealing, etc)

Now let’s look at the big picture of where we are with the motor, and what needs to happen. We have it all apart and documented, ready to begin restoration.  So let’s go!
There is not an exact order, but any time is great to clean and polish the metal hardware (screwheads, brackets, crankshaft – carefully!!), and get it out of the way. For heavy greasy grime use a rag soaked in solvent (e.g. mineral spirits). Rinse or wipe off and then polish with a nice product like Flitz or Autosol. Nice improvement!
Again, if ever you find the hardware heavily corroded, then replating or even replacement may be necessary. Depending on your location, someone who is very good (and reasonably priced) at metal plating can be hard to find, something to keep in mind!

Apart from the cosmetics, the major items on the checklist are to rebush necessary bearing points (will post on this soon), as the motor will get a constant workout. Then it is all about recovering and air sealing. The motor must be tight else the music begin to turn with a loping, queer motion, causing the music to lurch and stutter unpleasantly.
In order to be robust overall, this means the bellows, the slide valves and the trunk interior must all be tight individually.

Pneumatic recovery is a specialized topic which will be needed throughout the restoration process, so I will cover that separately in the next post.

The slide valves are basically just miniature wooden frames, covered on one side with motor cloth. Like a pneumatic, the cloth side must be well sealed. However just as important is a good seal between the trunk face and the inside of the valves. This is why both the valves and the trunk face must be lapped (a specific sort of sanding) completely and evenly smooth, so that they are well-mated to interface with each other.

Slide valve preparation

The preferred way of doing this, traditionally, is to adhere a piece of sandpaper to a solid, dead flat surface, such as a piece of plate glass or machined table (e.g. table saw). This ensures the lapping will give the desired result. Use a medium machinist’s square (6-12″ long) to sight across the valve surface of the trunk face. Depending on how much warpage or gap you see, you will need to lap accordingly. If there are significant gaps (more than a couple of mm), you will have to either begin with a rough grade of paper (e.g. 80 grit). Work your way up to medium (120-180). If there are only light distortions in the surface, then you can proceed immediately with a fine grit (250-320) to just even it out, and that should suffice.

Motor trunk lapping in progress

Incidentally, there is a detailed video of this process by (guess who?) John Tuttle. It’s a longer one, but worth checking out here.

We then finish up with a nice graphite lubrication, making sure not to mix it too light (or too heavy!) or put it on too excessively. Also, for valves like this which are in perpetual motion, don’t EVER use a greasy or “wet” lubricant for this application. This will eventually cause binding and performance issues. There might even be a warning sign about this from the original maker!

Lubricant warning for pianola motor
courtesy Paul Clement
photo by Lisa McManus Lange AKA “Sassy Scribbler”

The interior of the trunk should be proofed for leakage too; it needs protection from all leaks within and without!

Now here we would normally use a heavy shellac; the traditional choice for sealing internal channels. I am instead going to use a “modern” substance. This sealer, trade name “Phenoseal”, is a little like a thinned white glue. It has a water-like consistency when applied, and then sets up (but does not ever cure 100%) like a clear plastic membrane.
I would only agree to use this under certain circumstances: it is a significant time-saver, it does as good (or better) a job than shellac, it doesn’t cause other problems, in exchange for this convenience.
Given this criteria, It is vital that this type of product is never applied to a surface which needs to be glued or which contacts a moving part, and it is never used on a surface which will have to be refinished/resurfaced in the foreseeable future.
This is why we don’t ever, EVER, use a white or yellow glue for adhering parts which may need to come apart again someday. It is a bastard of a job getting these parts apart, unless hide glue has been used. Modern glues have many wonderful uses, but should only be used in permanent structural repairs to woodworking – that’s it!

So, we have covered prepping, lapping and sealing; I will discuss recovering separately. We also need to talk about rebushing, but as mentioned that will be a separate post as well.

Once the recovering, gluing and rebushing is done, your hardware is all clean and polished, you are ready for reassembly, then regulation!

See you on the other side!


Materials Spotlight: Burnt Shellac

Like Hide Glue, thick or “burnt” shellac  is another “sorta kinda” natural substance, the use of which is traditional in this industry and has been sanctified by time.

While it is undeniably interesting and fun stuff, it’s also just as sticky and messy as glue, so we don’t want to get too playful with it!

As the name suggests it’s simply a very thick formulation of regular, everyday shellac finish. In player piano actions, its primary use is as a sealant. It sticks to absolutely everything, which is good if you put it only where you are supposed to! As the carrier solvent evaporates the shellac slowly cures to a hard shell.

So it can be “painted” inside of block channels or also around the junction of metal bits into wooden blocks, etc. Once cured it is airtight, and won’t come off, unless you want it to. And here again, it is wonderfully “undoable” like hide glue.

Burnt shellac is also good to reinforce a fastened joint, which can’t be glued but still need strength. An example of this would be for the arm flanges of a motor. The flanges attach to the bellows with small screws, but as they are under a constant load, they need a little extra strength as insurance. However it’s not a good idea to glue them (as they may need to be removed for repair purposes), so shellac is a good compromise.

This wonder substance can be made in two ways: additive or subtractive. Note that the finished product is not exactly the same in both cases, as explained in further detail here.

The additive way is slower, but safer. Buy yourself a bag of shellac flakes (from a woodworking supply store), and gradually add a minimal amount of solvent (e.g. mineral spirits), just enough to dissolve the flakes. If you can get it right you will have a thick goopy mixture.

The subtractive way is the traditional way, as the other name suggests. Premixed shellac is bought from the hardware store, then “burned off” by lighting the liquid on fire, and letting it burn for such time as that it thickens to a goopy mixture. It will cool to a thicker consistency than that which it burns, so don’t overdo it with the burn off!

Burning shellac to thicken

For this method it is highly recommended that you do this out of doors away from combustible surroundings.

Disclaimer: I take no responsibility for any cataclysmic events that occur after the reading of this post!

Materials Spotlight: Hot Hide Glue

How do I love thee? Let me count the ways!

Hot hide glue is the ideal glue for many applications in instrument repair and rebuilding, and it has been the adhesive of choice for centuries, until the rise of synthetic glues in the 20th Century.

For wood to wood or leather to wood applications, HHG in this context is hard to beat! A quick rundown of pros and cons:


  • sets up quickly, allowing a higher rate of productivity
  • depending on nature of joint, high tack means clamping is often not required
  • viscosity can be adjusted (somewhat) to purpose
  • dries to form a “brittle” joint, which does not creep
  • water soluble, so completely reversible


  • sets up quickly, so workflow must be organized beforehand and executed efficiently!
  • needs constant source of heat at steady temperature, to maintain working temperature
  • water soluble, subject to moisture infiltration and therefore not suitable in warm environments with elevated humidity

So we can see that HHG has a couple of characteristics which may either be good or bad, depending on how we look at it.

The property of reversibility is a huge plus, where restoration is concerned. It allows a rebuilder to dismantle and break apart wood and leather joints without excessive damage to the constituent parts. And by rebuilding in the same manner, it pays forward the same courtesy to future restorers.

To make use of HHG, you need three basic ingredients: glue granules (sold at suppliers to fine woodworking trade), water, and heat. The source of heat can be any number of things, but again it should be a source of steady heat.

For me personally I have gotten my glue granules from Lee Valley or from Player Care. For the glue pot I use the industry standard “Hold Heet” automatic glue pot, from Emco. It’s available at any number of places online, and it’s the only glue pot you’ll ever need.

Emco “Hold Heet” glue pot

Happy gluing!