Repairing a jack hole in Mandolin side

[Chris Vallillo]

I've been restoring an early Gibson A for some time now (see "Pulling the Back off an early Gibson A" in the archives). Before re-installing the back, I had one last repair to do. Someone had drilled a hole for a pickup jack in the side and I wanted to patch this before I put the back on again.

I've been able to get a piece of birch milled to the proper thickness of the side (.092) and am getting ready to proceed but I had a couple questions.

I recall reading about a procedure to do this type of repair, perhaps in this forum, but have not been able to locate a post searching through the archives. I seem to recall there was a method to cutting and fitting a plug. Does anyone recall such a post or have any idea where I can find info?

The hole is approx. 3/8" across and poorly drilled; I assume I'd need to use a tapered teamer to clean it up before attempting to patch it. Also, since the side is bent, should I pre-bend my patch before cutting it out?

I'd appreciate any feedback the forum has to offer.

Thanks!

[Greg Robinson]

Hi Ginridge,
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[Chris Vallillo]

OK, I didn't see any profile info anywhere on the site. Is there a place to add this information?

Thanks.

Chris Vallillo

[Jim McConkey]

There is a User Control Panel link, near the top of the page (varies by layout), but you cannot change your own name. PM one of the moderators with your full name and we can change it for you.

[Steve Senseney]

If this were a large piece of wood, you would want to prebend it. At this size, it probably won't matter.

Looking at your project, I would use your reamer to get good clean sides, put a small circle of wood, and put a support inside of the instrument.

If you left the patch a little above the surface, you could scrape it down to the same height.

If this were a large oval, sometime the edges are beveled so that you have more gluing surface. At this size, I would not try to bevel.

If you have a tapered plug, you can put it into the side until you have a nice tight fit, trim off the outer layer and the excess inside also.

There are many ways to accomplish this repair.

Blending the finish over this will be the hardest part. Where it has a dark stain, this will allow you to hide any repair fairly well.

[Chris Vallillo]

Thanks for the feedback.

I was able to locate the article I was thinking of, a post on the Stu Mac Trade Secrets Newsletter, issue 75. It's available on their web site. It involved something called a bridge saver that cuts a beveled hole then cuts a perfectly matched plug. Sounds elegant, but costs about $150.00. A little rich for this project. I may get one eventually, but I tried to shortcut it by buying a 3/8" plug cutter from a local Farm supply store. Unfortunately, the jack hole was poorly cut and just enough larger that the plug I cut fits very loose. I could probably make it work with epoxy to fill the gap, but I'm going to look for a 7/16" plug cutter and try to use the reamer to clean up the hole just a bit and see if that will work. I'd assume that hide glue would be the best way to go, but would appreciate any thoughts on that. Also, I'd love to hear feedback on the Bridge Saver if anyone has used one.

Judging from my experiment with the 3/8 plug cutter, I'd agree I don't need to bend this ahead of time. There will be extensive re-finish work involved on this instrument face; tinting and french polish, so I don't expect the side to be too big a issue. My goal is to make this a player instrument, not a collector instrument.

I'll let you know how it goes.

[Steve Senseney]

Hot hide glue would have several advantages.

I have no experience with the "Bridge Saver".

[John Hamlett]

I have a "bridge saver", a handy tool for repairing warn bridge pin holes, but not a tool I would consider for plugging an old jack hole. I would cut the hole to a "football" shape and cut a matching (wood, grain, and shape) patch. Glue a thin patch inside to back up the shaped patch and make the repair. The "football" shape is much less visible, when well fit, than a round patch.

[Chris Vallillo]

I've ordered a tapered 3/8 " plug cutter to see if that will do the trick. I did need to ream out the hole w/ a tapered reamer as suggested and the straight 3/8 plug no longer fits.

I have a friend who mentioned that he has the Stu Mac bridge saver tool and if the tapered reamer doesn't "cut it" (pun intended), I'll try that and report back.

CV

[Chris Vallillo]

The 3/8 " tapered plug cutter finally arrived yesterday. It was rather rough on the stock and broke several pieces before I was able to get a good blank but eventually I was able to get a slightly oversized plug that fit perfectly. I'll start working on matching the color and will p[ost pics soon.

[Chris Vallillo]

Here are the promised shots of the repaired hole. The plug cutter was probably meant to be used in a drill press (which I don't have) so it was a bit rough on the plug, tearing some on the back side. The tapered nature of the cutter gave me just enough extra size for a good fit and allowed me to clean up the hole with a tapered reamer. I used slightly thicker material than needed and was able to scrape down the back a bit to clean it up.

I didn't brace it from the back since the surface area of the glue line was so great and the fit was nice and tight. A little Stu Mac tobacco stain created a fairly close color match which I'll fine tune when I get to the finish.

Thanks to all for the advice.