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!