Stambaugh Bass Chambering

A good customer had commissioned this bass from the Stambaugh company a few years back. It was ordered a little thicker than usual, and between this and its ash/walnut construction it was a bit heavy. I was told that they chambered it a bit, but maybe I could figure out how to remove more weight. My goal? To significantly reduce the weight of this instrument, while maintaining its integrity and aesthetic uniformity. 

I started by taking 3/16" off the whole back. Next I needed to uncover the existing chambers, so I began to tap the surface and identify hollow spots. Two holes were drilled which will allow me rout out the hollow area by means of a special flush trim bit.  The plan will be to chamber the sides and then apply bookmatched walnut caps to either wing. 

These are the factory chambers, fully exposed. There is some significant weight relief already (thank goodness), but I see much more that we can cut. 

Like so! You can see that areas crucial to the integrity of the instrument are left full strength (note the bumps around the strap pin screws!), but nearly everything else is gone.

So how best to manage the aesthetics? Initially I thought to cover the whole back with walnut, as the front is. A material constraint ended up with a happy compromise of walnut only on the "wings" of the body. This also allows us to lose that much more material. A nice clean ledge is routed along the neck-through, against which the walnut will seat. With a little luck this will look like it was made that way. 

After the walnut wings are applied, the edges are trimmed with a chisel. The original contours are carefully matched so as to minimize sanding work later. 

Next the battery and control cavities are

cut into the walnut, and the whole back is sanded in preparation for finish. 

The customer handily supplied the factory finish recipe (or quite close), and after curing a few coats this bass is assembled and ready for a new chapter! A full 1.5 pounds lighter, I might add.