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 Post subject: Brace location
PostPosted: Fri Dec 08, 2017 12:22 pm 
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Posts: 940
I've started to rebuild a Harmony Sovgerign "Jumbo" guitar. The main motivation was that it needed a neck reset, and one thing led to another. Now I'm planning to replace the ladder bracing on the top with an X brace pattern. So how should I lay out the X bracing?

I traced the outline of the body and sketched in one possible layout. I have no idea if it's reasonable or not. Should the X be flattened out more. so the upper ends don't go quite so far up and the lower ends don't go quite so far down? Or some other rearrangement?


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 Post subject: Re: Brace location
PostPosted: Fri Dec 08, 2017 1:42 pm 
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Location: Chadds Ford, PA
I'm guessing (incorrectly?) that the area of the top is close to a dreadnought. Perhaps the stresses on the bridgeplate and surrounding area would also be very similar where the dreadnought brace geometry might be sufficient for this jumbo. I would think that the bracing also needs to control for the boominess of the bass and also ensure good midrange and high range response with the larger-than-dreadnought sized top.


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 Post subject: Re: Brace location
PostPosted: Fri Dec 08, 2017 2:37 pm 
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Location: Hegins, Pa
since bracing is scale length oriented all you need to do is place the braces so the plate has the saddle about 1/8 in on the front .

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 Post subject: Re: Brace location
PostPosted: Fri Dec 08, 2017 3:32 pm 
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Locating the bridge plate is not a problem. But how tight or spread out should the X be? How far back of the sound hole should the center of the X be?

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 Post subject: Re: Brace location
PostPosted: Fri Dec 08, 2017 10:18 pm 
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Location: Hegins, Pa
what is your scale length?

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 Post subject: Re: Brace location
PostPosted: Fri Dec 08, 2017 10:21 pm 
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Joined: Fri Mar 03, 2006 7:09 pm
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Location: Hegins, Pa
you have to start with the bridge and saddle
you need the corners of the bridge to be supported on the X brace. As to the sound hole that really isn't the locator of the braces. If your using a 4 in sound hole then the joint of the X brace can be between 1 in to 1 3/8 in from the sound hole and the splay angle should fall in that 95 to 99 degree area to fit the requirement of the corners hitting the X

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http://www.bluescreekguitars.com


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 Post subject: Re: Brace location
PostPosted: Fri Dec 08, 2017 11:36 pm 
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The neck is not within reach at the moment, but I can tell you that the saddle on the current bridge is 11.25" from the front of the guitar body, i.e. 11.25" from the 14th fret.
The bridge is already there.

I will check where the ends of the bridge are relative to the proposed X brace and adjust the X brace as required. The current bridge is pretty big.

[edit] Scale length is 25-1/8".

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Everybody is ignorant, only on different subjects. -- Will Rogers
There are lots of people who mistake their imagination for their memory. - Josh Billings
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 Post subject: Re: Brace location
PostPosted: Sat Dec 09, 2017 11:06 am 
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Joined: Thu May 24, 2012 8:03 am
Posts: 637
Location: Chestertown Maryland
John Thomas is a guitar scholar, writer for Fretboard Journal, author of Kalamazoo Gals, and owner of about 200 cool guitars. He has documented guitar innards with x-ray, and done a bunch of them. Here is a story about some. This gives you a chance to see what is inside lots of classic instruments:

https://guitarkadia.com/emon/guest-post/the-true-adventures-of-the-great-guitar-x-ray-project/

Just search for guitar x-rays to see lots more. The 1930 OM in the article is cool to see.

Ed


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 Post subject: Re: Brace location
PostPosted: Sat Dec 09, 2017 11:59 pm 
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Location: San Jose, CA, USA
Thanks for sharing the link. That was very interesting, and seeing the X-ray images of the harp guitars was a real eye-opener.

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 Post subject: Re: Brace location
PostPosted: Sun Dec 10, 2017 7:55 am 
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Joined: Fri Mar 03, 2006 7:09 pm
Posts: 5419
Location: Hegins, Pa
https://www.tapatalk.com/groups/theunof ... -t847.html

this is a link at the UMGF that shows a number of tops that were taken back lighted so you can get more information

you may have to join to see the pics but it is an extensive library of information on tops

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Blues Creek Guitars Inc
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Board of Directors of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com


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