Soundboard Repairs

Without The Iron Frame

 Now that the iron frame has been removed from the piano, I was able to get started on repairing the soundboard and the notorious split.

As the photos show, there was quite a bit of dust and dirt on the board itself (there usually is on grand soundboards, being so exposed) but this was soon removed.

 

Dirt and Water Damage

After Cleaning

View Of Split in Soundboard

Two More Splits in the Bass Bridge

Opening The Split

Shim Glued and Inserted Into Split

Shim Flattened and Old Varnish Removed

Once the soundboard had been cleaned, two more splits showed up in the bass bridge.  It was impossible to see these when the iron frame was in place, as it completely covered them up.

Seeing these splits, I felt even more certain than ever that this was the cause of the buzzing sound which had been the biggest problem with the piano in the first place.

The next step was then to open the splits up more.  This is done so that the chances of the split getting larger by itself are all but eliminated, but also to make the split a uniform depth and width, so that we can insert strips of wedge-shaped wood, called shims, which fill in the split.

There is a special tool especially for this very process.  The shimming tool is basically a sharp spike cut in the same shape as the wooden shims, so that a technician can open the split to the exact shape of the shims which will be inserted.

The shim is then cut to the correct length, the edges shaped to fit the end of the split, and then is glued into place.

Once the glue is dry, the shim (a lot of which is still proud of the soundboard) is planed down level with the soundboard.  Abrasive paper finishes the job and gets the shim to blend in as accurately as possible with the rest of the soundboard.

The whole process of repairing the split inevitably takes off some of the old polish from the soundboard, so whenever a split is repaired, the soundboard needs to be repolished.  As is clear from the photo to the left which shows the shimming tool in action however, the old polish on the soundboard had become crazed with age anyway, so repolishing would have been recommended anyway at this point, even without splits.

The majority of the old polish is removed by scraping it off with a blade shaped for the purpose.  What remains is then removed by various different coursenesses of abrasive paper.  The varnish is removed from the bridges too.  Once flat, any small marks are filled with woodfiller, grain filler is then applied and the board is ready to be sprayed/repolished.

Repolishing the Challen soundboard will have to wait for several weeks as there is already a large Bechstein concert grand in the spray room which needs to be completed before another piano can be moved in.  In the meantime, I decided to begin the action work and key restoration 

Dismantling begins

After a long time getting other projects sorted, the Challen can now be properly started!

Removing the dampers

 I always like this part of the rebuild process.  It seems quite theraputic to be taking a piano apart every so often, rather than the painstaking process of putting everything together just so.

Even so, there is somewhat of an artform, even at this stage of the process!  The photos show several stages which most rebuild projects go through which I work on.

First, the dampers are unscrewed from the damperlift mechanism behind the keyboard, and can then be removed.

Bass String Rubbing

 Next, we measure the bass strings by doing a wax rubbing with a sheet of thick paper.  We also push the paper over the hitch-pins, bridge-pins and agraffes.  This rubbing will then get sent to a bass-string manufacturer who can accurately create a bespoke set of strings specifically calculated for the piano, to give the best possible tone from the instrument in the lower octaves.

Strings Removed

  
Once this is done, the strings can then be removed from the piano.  This is done gradually at first, reducing the tension throughout the piano evenly, so as to avoid putting too much pressure on any part of the frame and soundboard.  The strings are then mostly recycled, apart from one or two of the bass strings, which are sent to the string manufacturer as references in his calculations.

Measuring The String Lengths

As for the treble strings (ie, any strings which are just plain steel, not copper covered,) the length of each these is measured carefully.  We use this measurement to calculate the gauge of wire to replace on each note. (Notes near the top of the piano require a thinner gauge of wire from those further down.)  Thickness of wire is measured to within a small fraction of a millimetre.

Measuring Downbearing

Another thing we do at this stage is measure the downbearing of the piano.  Downbearing is a term which refers to the fact that, when the strings run along the length of the piano, they pass over a bridge (seen in the picture marked Measuring Downbearing, on the left), and this bridge should be slightly higher than the contact points of the string on either side.  On some pianos, this downbearing can disappear and need adjusting.  Running a piece of ordinary string is a good way to test this.  The Challen had no real issues.  Downbearing was still present, and little differences in the balance can be adjusted out later.

Removing the Wrest-Pins

After this, the wrest pins which are used to tune the strings were removed.  Several of these are measured to get their correct diameter, as we will need to put new, slightly larger pins back into the piano when it is restrung.

Following this, the bolts and screws which hold the frame in the piano are taken out.  It is common practice to put the screws in a piece of cardboard, as this helps to relocate them in their correct position later.

Taking the Bolts Out

Finally, the frame can then be lifted out of the piano!  This is another moment I like about the whole procedure; as it means you finally can get access to the soundboard underneath.  I'm hoping this to be the next entry in the blog, and will be able to talk about what we are doing to restore this important part of the piano to great condition.

The Frame Is Strapped Up To The Hoist

Lifting The Frame Out

The Iron Frame