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PostPosted: Mon Dec 04, 2017 6:42 am 
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Brazilian Rosewood
Brazilian Rosewood

Joined: Mon Jan 28, 2008 5:21 am
Posts: 3721
Location: Central PA
First name: john
Last Name: hall
City: Hegins
State: pa
Zip/Postal Code: 17938
Country: usa
Focus: Build
Status: Professional
it is all about the geomtery
here is how I prep the rim
https://www.youtube.com/watch?v=LrgRKKsxL-M&t=1131s
this is the initial set up I am shooting for
https://www.youtube.com/watch?v=TXfyVb3L3G0&t=142s

yes there are many ways to do this . Now this is more Martin style . The top is not entirely radiused

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PostPosted: Mon Dec 04, 2017 8:04 am 
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Joined: Wed Oct 08, 2008 11:36 am
Posts: 5149
Location: Southeast US
City: Lenoir City
State: TN
Zip/Postal Code: 37772
Country: US
Focus: Repair
Woodie G wrote:
This is fascinating! Who knew there were so many approaches! I was familiar with Mr. Cumpiano's building board technique, and has read about the tapering and wedging of the upper bout, but the photo essays were quite illuminating. Thanks so much to all that took the time to so beautifully illustrate your techniques and equipment!

The approach used in the build/repair shop where I spend my spare moments differs a bit, but works well for scale lengths and bridge placements from 3/4 size guitar (~20.5" scale and 12 fret neck) to 12 fret-to-body dreadnaughts (and ABG's where the string height is 9/16"). In summary: the upper bout bracing radius and glue-up is directly modified to ensure an natural fit for the fretboard extension at 1/2" string height over the top at the saddle location. Other than a method to accurately radius top bracing at both 28' and 60', no other jigs or fixtures are used beyond the basic outside mold for the body shape and the 15' and 28' radius dishes common to the radius dish/go-bar approach to construction.

Preparation: The rim is radiused at 28' for the top and 15' for the back. X-brace, tone bars, bridge plate, and fingers are radiused at 28', with the upper transverse brace radiused at 60'. Any sound hole braces and any upper transverse graft are left flat.

Execution: X-brace, cap, tone bars, fingers, and plate are glued up in the 28' dish. When dry, the remaining bracing (UTB, UTG, sound hole braces) are glued up on a flat caul, resulting in a preload that resists further flattening of the upper bout.

We fret after the instrument is finished and assembled, but I'm not sure that is really necessary to success. No wedges or tapering of the fretboard is necessary - the extension lies naturally on the top, and the fretboard gluing area is nearly dead flat (no further flattening of the area is done to fit the extension).

Again, thanks for the discussion!
This is the way I do it also. Has worked for me from Size 5 to Dred. I do the 60' radius on the UTB with a few swipes of a plane.

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These users thanked the author SteveSmith for the post: Bryan Bear (Mon Dec 04, 2017 9:06 am)
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PostPosted: Mon Dec 04, 2017 9:50 am 
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Brazilian Rosewood
Brazilian Rosewood

Joined: Fri Dec 14, 2007 3:21 pm
Posts: 2463
Location: Alexandria MN
One thing I forgot to mention in my blurb was that prior to tapering the upper bout with that sanding board the whole rim has been radiused to 30’ so it winds up essentially flat and tapered a bit above the sound hole and radiused to 30’ everywhere else.

Don’t ask me how I choose 30’, just pulled it out of the air about 14 years ago and stuck with it.

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Last edited by Terence Kennedy on Mon Dec 04, 2017 11:05 am, edited 1 time in total.


These users thanked the author Terence Kennedy for the post: Ken McKay (Mon Dec 04, 2017 6:57 pm)
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PostPosted: Mon Dec 04, 2017 10:15 am 
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Great thread! This is one of the harder things to understand

I radius all top braces to 30 ft, then plane a flat onto the middle section of the utb. Glue it in the radius dish, but put a few layers of tape on the top of the sound board underneath that flat spot. Then, I use Terry's jig to sand and fine-tune the soundboard after it's glued on. I usually end up with a little Fall Away.


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PostPosted: Mon Dec 04, 2017 7:17 pm 
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Koa
Koa

Joined: Fri Jan 25, 2008 9:55 am
Posts: 951
Location: Traverse City Michigan
Of all of them, Terrence's is something to take notes. Mine and the other plantilla or solera are very reliable but a bit odd in this modern world. And take note that in his method and especially that he added that he induces a radiused rim, his procedure achieves the goal. It doesn't matter if the rims are radiused or flat. Because the angle of the body under the fingerboard gets created by using the actual bridge measure etc... This will work in every case no matter the geometry of the sides and top curve.



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