Gluing in the soundboard

It has taken so long to get to the point where I am ready to glue in the soundboard that I have had a lot of time to think about the best way of doing it.

Professional harpsichord builders would use a go bar deck like this one from Michael Johnson's web site.

Kit builders usually end up having to use nails to hold the board in place while the glue dries, but after my experiences with using nails to secure the outside moldings to the case I have come to the conclusion that, while an experienced craftsman could probably do a very good job just using nails an amateur is probably better off using clamps if at all possible.

Even though I still have a long way to go before this instrument is finished, I am enjoying the process of building it so much that I have a feeling that it will not be the last one that I build and that makes it easier to justify buying a "few" more clamps as an investment ...

After carefully measuring several different types of clamp I came to the conclusion that a 12" Jorgensen light duty bar clamp would work both for this harpsichord and also for any other instrument that I might build in future.

So, finally, here is the soundboard being glued in:

There are a total of 51 clamps - 39 F clamps around the edge of the case and 12 small C clamps in the gap between the soundboard and the wrestplank.

I used liquid hide glue for the soundboard - not so much out of any desire for "authenticity" but mostly to take advantage of its longer open time - it took me almost exactly 20 minutes from applying the glue to tightening the last clamp.

Catching up

The soundboard was ready to go in almost a month ago but the weather did not cooperate with my schedule - there was a perfect weekend at the start of October, but I was away in Los Angeles and, by the time I got back, it had started raining an the relative humidity was up to 65% and the soundboard was showing some distinct curvature.

While I was waiting for the perfect day to glue in the soundboard I tried to finish up as many of the other small tasks as possible.

I varnished the legs:


and assembled several other parts:

The name board:

The jack rail:
and the music desk:

I also moved the case and the soundboard inside the house:

Fitting the outer moldings

I want to do as much work as possible on the case before I glue in the soundboard so the next thing to do is to attach all of the decorative moldings to the outside of the case and that means cutting lots of mitre joints.

The harpsichord kit came with a mitre box that has all of the correct angles for cutting the different joints which helps a lot. Fortunately I already know from past experience that I am almost completely incapable of getting mitre joints right the first time that I cut them so, accepting that inevitable reality I cut all of the joints with pieces of scrap wood first and then, when I have got them correct I cut the moldings to match.

Attaching the bottom molding to the bentside is going to be challenging - it is about 1/4" thick and, while it is just possible to bend it to fit the curve of the bentside it is going to be really difficult to attach it no matter how many nails I use. Eventually I decided that it would be better to bend the molding first before attempting to attach it so I built a form that matches the curve of the bentside out of two pieces of 3/4" plywood and an improvised steamer out of some 2" black ABS pipe and an old kettle. After steaming the molding for about 20 minutes I clamped it to the form like this.


I wasn't sure whether I had steamed the wood for long enough but, after leaving it clamped to the form overnight, it held its shape very well.

The top molding on the bentside was thinner, more flexible and much easier to clamp in place so I didn't bother pre bending it and just used lots of clamps.


Once everything was attached and all of the excess glue had been cleaned up it looks like this:

Thinning the soundboard and attaching the bridge

This weather was a little cooler this weekend and the relative humidity stayed around 50% for most of the time so it was a good opportunity to get some more work done on the soundboard.

The soundboard is 1/8" thick and has to be thinned down to about 3/32" in several places around the edges. This is really quite easy to do with a good sharp plane and the soundboard securely clamped down to the workbench. I started out very slowly and carefully getting the edges down to just the right thickness and then working gradually inwards. Things went a bit faster once I got some confidence in what I was doing and pretty soon it was all done.

Attaching the bridge was something that I was quite worried about. Gluing on the nut had turned out to be much more difficult than I had expected and I had a couple of near disasters while doing it although I was able to recover from all of them. The biggest problems were with the nails used to position and hold down the nut during gluing. The nut, which has exactly the same profile as the bridge has a "step" in it at the top - the nail goes through a hole in the lower part of this "step" and you have rely on the cardboard pads on the nail to distribute the pressure evenly. This turned out to be easier said than done and I dented the wood just a little in a couple of places, but fortunately was able to apply a damp cloth to those areas and get the wood to swell back into place. The second problem was getting the nails back out again! The wrestplank into which the nails have been hammered is made of oak - it is bad enough trying to get the nails to go into it and even more difficult to get them to come back out again. Of the 9 or 10 nails used to hold down the nut only 4 came out cleanly - the heads broke off all of the others. Of those I managed to get all but 2 out using a vice grip, but the last 2 just wouldn't move so I had to clip them off as close to the hole as possible and then trying hammering them just a little further in using a nail set.

So, when it came to the bridge (which was going to need 19 nails) I changed a few things.

The first thing that I did was to go looking for some stronger nails - I found some #17 nails which were quite a bit thicker than the ones that had been supplied but still fit easily through the 1/16" holes in the bridge. I also decided to use something better than just cardboard pads to cushion the nails and I found some small cork pads with a self adhesive backing that looked suitable. I put two of them together back to back and then attached half of a third pad to create a step that approximately matched the profile of the top of the bridge. I then added a cardboard pad on top to stop the nail from just embedding itself in the cork.

I then did a few experiments to make sure that I could hammer these nails into the plywood top of the workbench and still get them out again and reassured myself that it seemed to be possible.

So with lots of masking tape to catch as much of the glue as possible I went ahead and glued down the bridge. A lot has to be done very quickly to get the bridge positioned and nailed down so I didn't have time to take any pictures of that process, but here are a few shots of how it looked once the masking tape was removed.



Here you can see how the stack of cork pads compresses and deforms nicely to match the profile of the bridge.
... and this time all of the nails came out in one piece ...

There is still more work to be done to attach some wooden ribs to the underside of the soundboard before it can be glued into the case, but here are some shots of it sitting in place with the bridge glued down.

Attaching the nut

Before gluing down the nut I put it back in place and masked off the area around it to try to minimize the amount of glue that I will have to clean up later.


After the glue has set and the nails have been removed the nail holes are plugged with small pieces of wood and sanded smooth.


Here you can see the newly drilled wrestplank with the registers and keyboard in place.


A close up of the bass end of the wrestplank.


Finally a shot with the nameboard in place.

Drilling the wrestplank

This instrument has two sets of 53 strings so there are 106 tuning pins and 106 holes that have to be drilled. I put a block of wood along the front edge of the wrestplank so that I could use a drill guide for this operation. The holes are drilled at a slight angle so that they lean back from the wire at about 5 degrees.

Marking out the nut and the bridge

The harpsichord kit comes with a full size mylar drawing that is used to determine the position of the bridge (which is attached to the soundboard) and the nut (which is attached to the wrestplank).

The part of the drawing that represents the soundboard, the gap and the wrestplank is cut out and laid in the case.



The nut is positioned by drilling some small 1/16" holes through it and nailing it through the drawing into the wrestplank.


The bridge is positioned in the same way by placing the soundboard onto the workbench with the drawing on top of it, drilling holes through the bridge and nailing it down.


The bridge has already been bent to approximately the correct shape, but the curved portion towards the treble end still needs some force applied to it in order to get it to line it up in exactly the right position.


Here everything is nailed in place including the separate bass section that butts up against the main bridge.


Close up of the bass end of the bridge.