my mistake is now a feature!

 So as I noted previously, I tried a new glue on this build for the top and back plates.  It was a water proof glue meant for boat building.  Since I force my plates from flat to hemispherical I thought that maybe using heat and moisture might help the plates conform with less stress.  However, instead the glue just failed and let go, leaving the back plates hemispherical but not glued together.  They also would NOT go together without re-jointing.  So, I re-jointed and tried to glue them together, but with curved surfaces there was no good way to clamp them up and this is what I was left with.

I could have started over with different wood but my other option is to do something with the gap.  As seen in earlier pictures I glued in a support strip on the inside covering the gap.  This is a normal step but I did use a wider strip than normal.  Then, with the back glued to the body it was time to fix it.

I knew that I wanted to install a "zipper" to cover this.  Here is what I am calling a "zipper", it's a piece of inlay used on guitar backs or as purfling around the edge binding, etc.

Next step was a jig to guide the router while routing a straight groove across that curved, hemispherical surface.  I had the jig I'd used to create the radius dishes so I grabbed the guides that matched the 8 foot radius.  I cut square blocks that matched the width of my router base and nailed them between the radius guides.  Then these got clamped across the back of the uke body.

I used a speed controller on the router to slow it down quite a bit and proceeded to cut the groove.

Then test fit the zipper.

While most of the groove was a good fit there were a couple TINY gaps along side the zipper.  I grabbed a bit of sawdust from sanding these plates to thickness and proceeded to glue the zipper in place and then rub the sawdust into the gaps where the glue had squeezed out.  The masking tape should help a lot with cleanup later.

The zipper is proud of the surface by about 1/32" so the card scraper and sand paper should clean things up nicely after the glue is dry.  Looks like my earlier mistake is now a feature!

Brian