Domed Tops

For a long time now, guitar makers have been doming the tops of their instruments using various methods.  The top is domed for several reasons:

A domed top, like an arch, is stronger than a purely flat top with the same dimensions.

Wood expands and contracts due to relative humidity.  If a top is domed and glued at about the lowest level of relative humidity the instrument will see (usually, we don't like to see instruments get any drier than at 40%RH) a domed top can move much more easily than a flat top. That is, as humidity increases and the top increases in width across the grain, the radius of the dome will simply decrease rather than breaking the sides.  If the RH goes down, the top will sink rather than crack. For these reasons, I started to dome my tops with my second bandura but basically, I failed.  

I tried to dome my top by making a dished work board with an arbitrary dish to it.  I basically assumed that the rim of the bandura (the frame) would be level and gouged out a little dome into the workboard, less than an 1/8" at the deepest point.  I then profiled the braces so that they matched the dish of my workboard.

By the time I got everything glued up the little bit of dome I had worked into the design was almost gone because of forcing a dome onto a flat rim and the rest was gone once the instrument was strung up.  The other problem I had was that because the dome was arbitrary, it was very difficult to get the bridge to match up exactly to the top so I used epoxy when gluing to fill the gaps.  Here's the plan for the next instrument.

Hanging out on a lot of guitar maker's forums over the last several years, I learned that many "flat top" guitar makers used a spherically dished workboard to build the dome into their tops.  They use that same workboard to "profile the sides" or shape the sides of the guitar so that they match the 3D aspect of a sphere.  My first two tries at doming had flat rims (i.e. they didn't match the 3D profile of the dome) for this next one, I've purchased a dished work board with a 25' radius.

You can see how guitar makers profile the sides here I used a very similar method when I built my first guitar to learn how to do it except I used a motorized table to make the sanding go faster.  The rims are much thicker on a bandura so I wanted it to be motorized to make the job easier.   I profiled the sides a few days ago and it worked fine.

Next steps:  The next steps coming up will be to glue the neck to the rim, the rim to the back and begin bracing the top.  In my next post, I'll have some pictures of all of the components and how they go together.