Repair Gibson K-1 mandocello

Hi,

I posted a question about this instrument a few years ago and it was discussed briefly. I have decided it is time to open it up and fix it and I was wondering about two possible options.

I have a 1936 Black face K-1 and is is excellent shape except that about 10 years ago it developed the dreaded top sag under the bridge disease. -- a common ailment in these under built instruments.

I did not play it long after it happened so the problem a this point the sag is "reversible". That is when string tension is slack off the top rebounds to its proper carved contour. I have looked at Frank's repair of the 1920 K-2 mandocello on this site and propose to open the back and make a similar repair on this instrument.

I will not have to do all the heroic efforts that Frank did to return the top board of the instrument to proper shape however nor will I have to do any work on the end blocks. So this is a much easier repair I hope.

So my question is this what do folks think of using an X-bracing for the top rather than the second transverse brace under the bridge that Frank used? The X-brace idea is stolen from Bruce Weber's discussion of a oval hole Weber mandocello that he built a few years ago.

SEE PICS

My goal is to stabilize the top and yet make a minimal impact on the K-1 tone/sound. Would anyone want to wax eloquently on the pros and cons of these two approaches.

Bernie Daniel

Attachments:

FFord repair1.jpg, 217 KB
X-brace used on Weber mandocello.jpg, 187 KB

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Permalink Reply by Bernie Daniel on May 1, 2015 at 2:22pm

Well I feel like I've just gone through a graduate course in taking off and gluing back mandolin tops and maybe I have. Between all this and Frank's initial section I ought to stand a pretty good job of getting it right -- eventually anyway!

You've done a terrific job of documenting things with pictures Paul I'm going to try to remember to also take photos at every step-- no excuse not to with cell phones these days -- the problem is remembering to do it.

Very fist thing I do when I get that back off is to lay it down on a large piece of drawing paper and make a tracing of it. That is so I have a record of the original size and also I will use that trace as a template to cut out a piece of 3/4" plywood to drop in the the cavity when I am not working on it to keep the ribs for flexing inward as well.

For clamping I plan to use the set of spool clamps I made for gluing mandolins only I'll change the bolts to 5" so I can open them wide enough.

I'll probably think more about this whole project for a week or so before I start doing any work on the instrument.

Thanks for all the insights!

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Permalink Reply by Ned Knepp on May 1, 2015 at 4:50pm

Bernie, the grad course starts when you pull the back on your mandolin.

Whatever, it should be fun.

I agree with Paul about the using L brackets to support your instrument. A form will do a much better job and do it more easily. The brackets are a repair device and are wonderful for pushing the sides around as needed but would be a major pain in the neck to use them just to hold the shape of the body.

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Permalink Reply by Bernie Daniel on May 3, 2015 at 10:08am

Getting ready. I'm going to make a form to hold the sides but since the flare out will be at the top only I propose to make it out of 3/4 finishing ply and put "legs" on it so it holds the upper 1" of the ribs in place. Couple of pics.