finish cracks

[Bob Schmidt]

The bouzouki I built has developed some finish cracks around the tailpiece. The tailpiece bottom screw has also pulled out a bit. I don't see any distortion on the body itself, and the string pressure calculations come to 74.7kg which I don't think is out of the normal range. The bridge angle is 18 degrees which I don't think is too excessive.
Can I assume that this is strictly a finish issue, or is something with the bridge the issue? The finish is nitrocellulose lacquer, and I am not sure of the thickness. I did not use filler on the rosewood because I did not like the way it changed the rosewood color, so I filled the grain with successive coats of lacquer, wet sanding every 2 or 3 coats.
Attached are a couple of pictures.

[fscotte]

Looks like something is loose. It’s cracked all along the center insert there.

Lacquer cracks act like a stone chip on your windshield. Always follow it back to the stress point. The whole tailpiece area looks suspect, and the screw pulling out should be an indicator.

I’m also not a fan of those Ashton tailpieces. They never seem to fit consistently.

[HoGo]

The recurve under the tailpiece looks quite deep and not smoothly curved (just judging by the reflections in the second pic). Isn't the top slowly folding in that area? Slow rotation of the block and top failure could explain the whole cracking issue.

[Bob Schmidt]

The recurve along the back appeared a bit deeper then around the sides when I carved it. I think it is because the transition to the bridge is a bit steeper from the back. It was carved to 3.5mm.
Would there be a way to determine if it is rotating? For instance if I measured the height from the tailpiece to the top under tension and relaxed would I expect to see a difference.
Thanks for letting me now how to read the cracks; I do see they eminate from the tailpiece strip edges.

If there is in fact movement, is there a way to repair it? It is my first instrument, and I expected some learning experiences, but I am really enjoying playing it and would hate to have to start over.

After installing the tailpiece I have to agree with you it seems that it would be better suited on a mandolin. I wanted to match the tuners color wise, and I liked the idea of being able to use either loop or ball end strings, but it seems very narrow for this instrument, and the screws are pretty small. The dimensions are such that I did not see anything available to replace it that would cover the bottom screw hole.

[HoGo]

My first ended similarly. :-)
The top was quite thin under tailpiece and the recurve started going deeper and eventually the centerjoint opened under tailpiece slightly. I mended it by adding flat piece of crossgrain spruce inside (largish cleat) but eventually I replaced the top and the mandolin is fine since then. Generally the top was weak and would go sooner or later.
On other mandolins with such diagnose (we cannot be sure just from the pics if it is really the same in your case, but 3.5mm for octave seems thin to me - most folks keep mandolin topsalmost that thick under tailpiece) the recurve can develop crossgrain crack right at the deepest spot under tailpiece.
On mandolins that have shallower, less curved recurve under tailpiece the weakness of top can show on the arch right between tailpiece and bridge where the top will bulge sometimes even touch the front edge of tailpiece and eventually the seam will pop open and be almost impossible to close for gluing.
I would keep my eye on the area around and under tailpiece and watch if it tends to detune more than is common.

[artdeco]

Is the tailpiece an actual Ashton-Baily or one of the knockoffs from China. I sprung for a couple of those knockoffs and discovered that the mounting area was not 'flat'. In pic 3 it looks like the area where the bottm screw is pulling out seems to have a kink in it, exactly as I experienced with the ones I have. I managed to straighten them, but it was dicey bending cast bronze.

[fscotte]

Right, the tailpiece itself may be the only factor here.

If not perfectly matched to the rim, will substantially increase pressure on a smaller area.

Why I still like the Gibson style tailpiece. Strong enough, but flexible enough to shape itself to rims contour. It's a tried and true method that has lasted a century.

[Bob Schmidt]

It is an Ashton-Baily tailpiece. I bought it from Stewmac. I am seeing your point about the small and rigid contact area. The instrument is staying in tune so if there is any contour changing it is not fast. I will be doing some work on the neck now that I have played it for a couple of months I want to change the neck angle a bit so I will take a closer look at the tailpiece, endblock, top etc. to see if There re any other issues.