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Old 08-13-2010, 12:21 PM
Misty44 Misty44 is offline
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Default #3 and #4 Back Braces

I will be replacing the number 3 and 4 back braces in a 1976 D-18 and have several questions:

1. What were the original dimensions for those braces for that year?

2. Given a choice, what size braces would you use for optimum strength and ...how shall I say it... enhanced tone (e.g. less dampening, more energy, fuller rounder bass, etc. without thinning out the sound)? I'm not addressing the top or popsicle braces, just the back #3 and #4.

I've seen specs for a 1937 D-18 that used 3/8" (wide) by 1/2" (tall), and I believe post-'90's D-28GE's come with 3/8" x 3/4" braces that some owners cut down (modify) to 3/8" by 1/2" (same as the pre-war) to help achieve those characteristics I mentioned above.

Any info on the original specs and all opinions about what dimensions I might use now would be much appreciated. Many thanks.
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Old 08-14-2010, 05:53 AM
Brackett Instruments Brackett Instruments is offline
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I've got a 1974 D18S that's due a string change. I'll measure the braces when I have the strings off.

Why are you replacing the braces? I'm pretty sure the original braces are tucked into the linings. That's going to make replacment difficult. (you probably already know this)
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Old 08-14-2010, 07:59 AM
Misty44 Misty44 is offline
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Thank you Woody, I appreciate the effort.

Mea culpa, I am using the D-18 as my "test bed" for self learning about the in's and out's of acoustic guitars. I have several other acoustics acquired for their voices and have no plans to touch them, but the 18 was in rough shape when I picked it up expressly with the intention of tinkering with it. I was a finish carpenter and cabinet maker and looking for a new application that combined my love of wood, tools, problem-solving, and guitars, and working on this old beat up Martin has been extremely satisfying in that regard.

Using the go-slow-and-test-frequently method, I have so far enlarged the soundhole by 1/4", added a cross-brace to the end of the bridge plate to boost the bass, sanded (scalloped) some of the top braces, and removed about 50% of the popsicle brace (tapering it down from the center to the ends). I've also slotted and reamed the bridge, and made and replaced the saddle and nut.

Each procedure produced -- to my ear -- a beneficial result, namely more volume and sustain, better bass response, and an overall richer, deeper tone.

However, I believe I went too far sanding down the 3 & 4 back braces, which resulted in the guitar sounding airy, echo-y, and stripped of its tonal essence. Do you think I'm correct in assuming this is the cause, can lowering these braces produce such a dramatic effect?

So I've set myself a new challenge to replace those braces, and realize I'll have to install them under the kerfing. I don't know the original size, but am leaning toward the 3/8 x 1/2 inch dimensions.

Woody, any thoughts you have that could validate the effects of what I've done to the tone as well as the optimal size of the braces I should now use are appreciated. Many thanks.
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Old 08-14-2010, 08:56 AM
runamuck runamuck is offline
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Quote:
Originally Posted by Misty44 View Post
However, I believe I went too far sanding down the 3 & 4 back braces, which resulted in the guitar sounding airy, echo-y, and stripped of its tonal essence. Do you think I'm correct in assuming this is the cause, can lowering these braces produce such a dramatic effect?
I really doubt that the changes you made to the back braces have had the kind of effect you describe here.

It seems to me that the other modifications you have made, such as enlarging the sound hole, tapering the top bracing, etc., are the causes of the changes you describe.

Jim McCarthy
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Old 08-14-2010, 11:11 AM
Misty44 Misty44 is offline
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Thanks Jim for the reply.

The various modifications I made were done in stages over a year beginning with the soundhole enlargement, then the top braces, the cross brace, and the popsicle brace, each a separate, disparate procedure. All was well after each one.

But then last week I started in on the two back braces after which developed the airy, open, no-meat sound. So my instinct is to roll back time to the last point where things were okay.

A few days ago I placed two 3/8" x 1/2" back braces (that I haven't gotten around to re-gluing into a 50 year old Gibson) up against the front and back of the #3 and 4 braces and held them tight by wedging a thin piece of pine between them running along the center seam. This has made a significant improvement in the tone and got me at least half way back to where I had been.

I was therefore encouraged by this result to proceed with getting the braces back to the original height before I took sandpaper to them, and hence my initial query. But my thinking may be flawed. So today I'm trying to figure out a better experiment to restore the lost height than the pressure fit I've rigged using the two Gibson braces. I think I'm on the right track, but probably won't be certain until the braces are properly replaced. If that doesn't do it, then ** gulp ** I will have to start thinking about those top braces.

Thanks again.
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