Before the top can be attached to the body, there are a few more things to do. First, decide how to progress; during steaming, the top had separated into three parts (as expected) since the old piano soundboard was made of strips about 10cm wide.
The three sections had been kept in the forming mould, but did spring back a bit when released. So I decided that it might be best to fit them individually, rather than try to re-glue them into a single curved piece before attaching it to the body. That meant measuring up, and cutting the sound holes in the right places, and adding the bass bar, before attaching the pieces to the body. Here’s the bass bar being glued:
That also made a decision for me that I’d been thinking about. I was thinking of putting the bass bar on the “usual” side (as in a violin or viola, on the side of the lower frequency strings), and the sound post on the “usual” side for a violin or viola. This is not how the old kontrabas instruments were made! It is clear from Swedish museum photos (example) that the sound post was on the “bass” side, and also is fitted into the bottom of the instrument, rather than being wedged as in the violin family.
So that meant I also really needed to cut the hole for the sound post before fitting the top – which I have done, on the “bass” side as with the traditional kontrabas nyckelharpa. This is because if it were on the other side, the soundpost would have been close to a join in the top, which I thought not ideal.
However – there was a problem! When I started fitting the pieces of the top, I discovered that during steaming a crack had started in one piece – though not in an important place, and most of it would have been cut away after the top had been fitted. More importantly, another crack developed in the centre piece as I started to fit it before gluing. I suspect that the soundboard from the old piano (nearly 100 years old) had dried out so much that the wood has become very dry – and even steaming has not made it as flexible as newer wood could be.
So, I have decided to go back to my original plan (before I thought of using the old piano wood) – I will form the rough shape of the top by gluing pieces together, then cut out the curved top in a similar way to how I made the belly curve of my wire strung harp.