Re: Bowlback Mandolin Projection
Originally Posted by
Sam Brown
I'm doing some work on a bowlback mandolin for a friend of mine, and when I got it the transverse brace above the soundhole was partially missing and the instrument had basically folded in on itself. I spent a couple days trying to coax as much of the distortion out of the top before pulling the fingerboard and replacing the transverse brace, I intend to add two more on either side of the soundhole to ensure the top doesn't get any worse.
Since I couldn't pull most of the distortion out of the top, the neck angle is basically non existent, so I glued a wedge underneath the fingerboard, and I'll taper it toward the nut end to raise the projection, but I have no idea what a bowlback mandolin projection should be. I should add the current bridge has been shaved down a lot and I intend to replace it entirely so I don't want to base the projection off of that.
tl;dr When placing a straight edge on top of the frets, how much much distance should be between the top of a bowlback mandolin and the bottom of the straight edge?
Great question, Sam, and I hope it scares up some replies in a section mostly devoted to arch-top mandolins.
I've been down this same road many times and it is a fun, if challenging territory. Sounds like you are intuitively thinking and working smart.
Unfortunately, I'm out of town and away from my bowls, but Jim Garber or someone can certainly weigh in and take some measurements from their instruments on the 'relief angle' so to speak of the shimmed fretboard. I've done that job on a number of bowlbacks, myself.
Unfortunately, on the Italian mandolins I've attempted this fix...for the same reason of the top collapsing around the soundhole....the problem was compounded by the fretboards being super thin...with the frets often apparently cut after the fretboard was attached...so they would come apart in pieces. With the US bowls the fretboards are typically much thicker and you can get them off, shimmed and back on easier.
The mini-braces to the sides of the soundhole is a great idea. Luigi Embergher used these on at least some of his instruments I've seen disassembled. Alex T or someone more knowledgable can confirm if that was a regular practice. I've embraced that and have added those braces on all my bowls. Hasn't effected the tone to my ears..and if it's good enough for LE then it's a good practice, I think.
What it implies to me is that folks all the way back then were savvy to this potential problem. Both Embergher and Martin in the US added a small stiffener plate between the neck block and the top brace you mentioned to help address this potential problem.
I've done the same thing for my bowls. I want them to remain playable...
Good luck with the project. I'm sorry I can't answer your specific question about the projection angle / bridge height, but someone will shortly for sure.
Why not post a few photos of the project? Not many bowlback repair adventures get covered here and there's a lot of great, affordable instruments out there that need help. And not very many folks--at least here in the States--willing to take on the kind of major triage you're talking about.
Mick
Ever tried, ever failed? No matter. Try again, fail again. Fail better.--Samuel Beckett
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