Cracked Skid Board and More Stripped Screw Holes

This post is a continuation of the Milton Player Piano Series.

This time, I'll be repairing the skid board, which is the plank that makes up the bottom of the piano. The pedals, pedal rods, and blocks that the bellows mount to are all attached to the skid board.  

As you can see in the next few pictures, there are several large cracks running the length of the skid board.  This has caused the skid board to sag, which in turn prevents the pedals from working properly.  Also, most of the screw holes in the skid board are stripped out.  This prevents the pedal components from being firmly attached.

Before repairing the skid board, I remove all of the hardware that is attached to it.  There are a lot of pieces to keep track of here, so I number the bottom of each piece I remove, as well as draw a simple diagram to help with the reassembly later.

In order to make gluing and clamping the skid board easier, I use my Roll-Or-Kari Piano Moving Handtrucks to easily lift the piano an extra few inches off the ground.

The next step in repairing the cracks is to spread them slightly by tapping in a couple of wedges.  This will make it easier to get the glue all the way through.  Once the crack is opened up, I brush in some Titebond II, trying to get it all the way to the bottom of it along its whole length.

To clamp the skid board, I use these 3/4"  threaded pipe clamps along the underside of the piano.  After clamping, wipe off any excess glue with a damp rag.  Allow this to dry for 24 hours.

After the glue has dried, I attach these mending plates just for extra security against the crack re-opening in the future.  Any irregularities in the top of the skid board can also be smoothed out with a small block plane.

Now that the cracks have been repaired, I can move on to fixing the stripped screw holes.  The first thing to do here is to draw a large x through the center of each hole to be repaired.  This will assist in redrilling the holes in the exact same location later on.

After the X's have been drawn, I enlarge each hole with a 3/8" Forstner bit to about a centimeter deep.  I then proceed to glue a 3/8" plug into each hole, making sure to align the grain of the plug with the grain of the skid board.

This repair must be performed using plugs, not with dowel pins as the grain of a dowel pin runs the wrong direction.

Once the glue has dried on these plugs, the last steps are to extend the X's that I drew previously onto the plugs, make a dent precisely in the center with a sharpened punch, and predrill each hole with a bit that is the same size or slightly larger than the shaft of the corresponding screw.

After each plug has been predrilled, the pedals and pedal hardware can be reinstalled.

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Kimball Damper Pedal Repair

The damper pedal on my Kimball upright snapped in half the other day.  This is not a particularly common problem to have, and the repair involved some metalworking (which is a field that I suspect most piano technicians don't have much experience in), so it seemed a great candidate for my first blog post.

The repair process involves removing the broken pedal from the piano, cleaning both pieces, brazing them back together, sanding the repair smooth, and reinstalling.  Normally to remove a pedal on this piano, the entire piano must be tipped onto its back to remove the screws that hold the toe board on.  The toe board is the horizontal piece of wood that has square holes for the pedals to extend through.  In this case, the front half of the pedal was broken off and so the back half could be slid back through the toe board and removed from inside of the cabinet.

There are four screws that had to be loosened before the pedal could be removed.  The pedal operates by pivoting on a steel pin that is held on either side by a block of wood.  Also, note the steel wire that acts as a spring to return the pedal to its resting position when downward pressure is released.  Once the four screws are loose, the wood blocks can be pulled away from the pedal, and the pedal can be pulled out toward the top of the picture.

Here you can see the pin that keeps the pedal from being pulled out of the front of the piano while the toe board is still in place. The pin can now be popped out with a hammer and punch.  Removing it will allow me to later reinstall the pedal through the front of the toe board, and then tap the pin into place through the wood blocks and back through the pedal itself.  While I have the pedal removed, I will also replace the felt bushings on the pin that reduce friction and provide quieter operation.

A clean joint is imperative for creating a strong bond while brazing.  I use multiple grits of emery cloth for cleaning up these joints.  Here you can see the clean joint that is ready to be fluxed and brazed.  

I've recently acquired a new brazing system.  I still have my old setup with standard oxygen and acetylene tanks and Smith torch and regulators which I will use for heavier duty brazing and cutting.  The new setup is much lighter duty and consists of a BBQ propane tank, a medical oxygen concentrator, and a lightweight Smith torch.  The main advantage to this system is convenience.  I only have to go 5 blocks to the nearest Walgreens to refill the propane, rather than 12 miles to refill my acetylene and oxygen.

My old brazing setup.

My new brazing setup for light-duty work.

With my joining surfaces cleaned up, I brushed on my "Stainless Light" Silver Brazing Flux from Cycle Design USA and proceeded to fire up my oxy-propane torch.  I brazed the pedal back together with 56% silver (also from Cycle Design USA) which worked fairly well.  

I did end up with a small spot that didn't fill in.  I think the pedal was just a little too thick for this torch to be really effective.  The oxygen concentrator can only put out about 8-9 psi, and I'm still figuring out the right pressure ratios.  It seems the propane needs to be at much higher psi than acetylene does for brazing.  On the bright side, the joint survived my testing, which consisted of holding the pedal on the square end and banging the round end against the table.

Flux applied to pedal.

Pedal after brazing and before cleanup.

With the brazing done, I filed down the excess filler and sanded it smooth with emery cloth.  I then reinserted the pedal through the toe board and tapped the steel pin back into place with the new felt bushings.  I could have applied some kind of clearcoat to the pedal to keep it from rusting, but with the amount of friction this pedal will see against peoples' feet, I think I will just give it a rubbing of mineral oil every once in a while.

Pedal post-cleanup.

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