Dip in Bridge Area

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sjhouska
Posts: 19
Joined: Thu Feb 24, 2022 1:09 pm

Dip in Bridge Area

Post by sjhouska »

Now that I have closed the body on my Martin 000 kit, it has been pointed out to me that there is a 1/16"(perhaps 3/32") side-to-side gap/dip in the center of the top where the bridge will be mounted. The gap is obvious when I span a metal ruler between the side rims but, curiously, there is no visible gap whatsoever when I simply lay my bridge down on the top. This is my first build and I am wondering what, if anything, I need to do to correct or compensate for the gap.

Two possible solutions have been suggested to me. Either change the angle of the neck when I am setting the neck in the dovetail joint, or glue a 1/16" spacer to the bottom of the bridge, or perhaps a little of both. But I am reluctant to pursue a solution given that there is no visible gap when I lay the bridge on the top and I have no experience (other than this build) in woodworking, I want to end up with a playable guitar with decent action.

Any and all input will be appreciated.

Gratefully,

Scot
MaineGeezer
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Re: Dip in Bridge Area

Post by MaineGeezer »

Has the humidity in your shop changed significantly (gotten drier) between the time you glued the braces on and now? If so, the top may have shrunk in width, the braces won't shrink significantly in length, and it's quite possible to pull a convex radius into being a concave radius. The bridge plate might be enough to keep that area flat so your bridge sits on it okay.
You can try putting the box in a high humidity environment (put it in a sealed-up trash bag with a sponge) for a few days to see if it fixes itself.
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Diane Kauffmds
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Re: Dip in Bridge Area

Post by Diane Kauffmds »

Can you post a photo?
Diane Kauffmann
Country Roads Guitars
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tippie53
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Re: Dip in Bridge Area

Post by tippie53 »

RH will cause the top to rise ( higher rh ) and dip when its Lower
so pictures and tell us where your at
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Kevin Sjostrand
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Re: Dip in Bridge Area

Post by Kevin Sjostrand »

This happened with the OM I completed last month. The top where the bridge mounted was still perfectly shaped for my bridge. I glued it up, finished assembly and strung it up and did a set up. It was barely noticeable as the string tension did pull the top a tiny bit. After 4 weeks in the case in a more controlled environment it the top has come back and the bridge rose another 1/32". I'll drop the saddle to get the action back.
All to say you may be okay.
Diane Kauffmds
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Re: Dip in Bridge Area

Post by Diane Kauffmds »

That's my first thought; just glue up the bridge when the time comes. I think it's a humidity issue too. It's easier to advise with a photo.
Diane Kauffmann
Country Roads Guitars
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sjhouska
Posts: 19
Joined: Thu Feb 24, 2022 1:09 pm

Re: Dip in Bridge Area

Post by sjhouska »

Thank you to all who responded. Unfortunately, I don't have the tech savvy to upload pics from my phone right now but, with luck, I may be able to upload pics at the end of this week.

Relative humidity (RH) is likely the issue. I have been haphazardly using a small humidifier in the room where I keep the guitar when not working on it (now that I think about it, the braces were rarely in the room that I "attempted" to humidify), but I don't have a hygrometer to measure humidity. I live in a dry region - today is cloudy and the RH is 20%. It is typically in the single digits and low teens. The top braces were glued on during a period when I was doing a better job of plugging in and refilling the humidifier. I haven't been very good about the humidifier lately, leading up to gluing the top.

Just ordered a new humidifier this morning with a larger reservoir and a hydrostat.

Your input is greatly appreciated. This forum is an incredible resource for this newbie!

Scot
Diane Kauffmds
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Re: Dip in Bridge Area

Post by Diane Kauffmds »

Rh is my guess. Since your humidity is that low, you can do 1 of 2 things:

1. Keep it in a room, or closet, with your humidifier, for a few days.
2. Wet a couple of sponges, place them in a closed plastic container with holes. Close the box and sponges in a big trash bag for a couple of days.

#1 is preferred, because you have some control over the rehumidification.
Diane Kauffmann
Country Roads Guitars
countryroadsguitars@gmail.com
sjhouska
Posts: 19
Joined: Thu Feb 24, 2022 1:09 pm

Re: Dip in Bridge Area

Post by sjhouska »

I was able to get the pics on my computer before leaving town this morning . . . Here are 3 views of the dipping top:

In case it matters, when I place the body top down on a flat surface and press on the neck block area (pressing on the back), the top tail block area does pivot up away the flat surface

Thank you for your interest and help!
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Diane Kauffmds
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Re: Dip in Bridge Area

Post by Diane Kauffmds »

That can be from 2 sources:

1. Lack of humidity. With what you said about your rH, I'm sure it needs hydration.

2. The x-bracing can relax, losing the appropriate curve, if the braces have been thinned too much (too much height off). I don't know how much you may have continued shaping after installing them. If the low areas on scalloped bracing are less than 1/4", they'll darn near straighten, creating this dip.

First, I'd hydrate it. See what happens in a couple of days.
Diane Kauffmann
Country Roads Guitars
countryroadsguitars@gmail.com
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