OO cutaway

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joel
Blackwood
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Joined: Thu Oct 11, 2007 7:55 pm
Location: Brisbane, Australia

OO cutaway

Post by joel » Sun Apr 14, 2024 7:11 pm

Good Afternoon all,

Well, No.2 is officially finished. This one only took 18 months...

It's an OO size, 12 frets to the body, cutaway using the building techniques I've very amateurishly applied from "The Books". Body 460mm long, 360mm wide at lower bout. Too many mistakes, blunders, and mishaps to list. Which lead to multitudinous re-do's, reworks, and repairs. Learned a lot. Cursed a lot. Mostly enjoyed it.
OO front 2.jpg
OO Back 2.jpg
The knot you see in the neck only became apparent as I was carving the profile. Rather than start again, I filled with saw dust and superglue and kept on going. Worked out OK, and now it's a feature... not a fault.

Finished build tap testing resulted in;
T(1,1)1 - 109Hz
T(1,1)2 - 197Hz only 1 Hz off G at 196Hz. It really did make the guitar jump on the low G!
T(1,1)3 - 232Hz.

Turns out my build was very sensitive to adding side weight and so I only needed half of what Fig. 2.3-15 suggested. Adding 2 steel sections of 70mm x 40mm flat bar equalling a total of 233g side mass.
New tap testing results:
T(1,1)1 - 108Hz
T(1,1)2 - 190Hz - between F# and G. Very nice! No more boomy G's.
T(1,1)3 - 226Hz.

I measured top deflection using 2 different weights;
1. weight: 477g = 4.68N. deflection: 0.05mm. K = 93,600N/m
2. weight: 957g = 9.39N. deflection: 0.11mm. K = 85,363N/m

I used the average of these - 89,482N/m to calculate monopole mobility of 13 x 10(-3) s/kg. Which according to Design section 1.7.2 makes this guitar officially "Good"! Sure sounds good.
- If God had intended us to drink beer, He would have given us stomachs. - David Daye.

- The mouth of a happy man is filled with beer. -

Dave M
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Posts: 599
Joined: Tue Jul 15, 2014 6:44 am
Location: Somerset UK

Re: OO cutaway

Post by Dave M » Mon Apr 15, 2024 2:37 am

Joel I like it. I appreciate Trevor's body shape, and particularly the straight saddle with enough room for intonatation. Once you get used to that the slanted saddle always looks awkward to my eyes.

As amateurs we have to but up with the cock ups, minor and major but as you say one can still enjoy getting to the end result.

The fact you've been able to get the frequencies where you want them is impressive. G&G's methodology does work!
------------------
Dave

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WJ Guitars
Blackwood
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Location: Sutherland NSW
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Re: OO cutaway

Post by WJ Guitars » Mon Apr 15, 2024 12:29 pm

Joel a very interesting story for a successful guitar build! Every time I build a falcate braced guitar I am always referring back to Trveor's Books and videos for guidance. You next build will have less cursing.

How does this guitar build sound?

Wayne

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joel
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Posts: 290
Joined: Thu Oct 11, 2007 7:55 pm
Location: Brisbane, Australia

Re: OO cutaway

Post by joel » Mon Apr 15, 2024 5:13 pm

Thanks for the kind comments.

It sounds good! Louder overall than I expected from a small body. Lower notes are stronger than I expected based on the relatively high frequency response of 108Hz. Upper mid range voice is stronger than on an X braced guitar. If I want to strum along to a song I need to really pay attention to how hard I hit the strings due to that stronger mid voice. I imagine in a band setting it would really cut through and work quite well. Since the majority of my acoustic playing is (attempting) fingerstyle blues it works out really, really well. Very nice sustain, the body really vibrates along with the notes. Sympathetic harmonic vibration is pretty strong if I forget to dampen the strings I don't want to ring out.

I suspect if I had caught the error in my top thickness calculations early enough, and if I had a way of properly figuring out how much carbon fiber I was applying to the braces, I could have had a "better" guitar than "good". Top is about 0.4mm too thick for the body size, and I probably overdid the carbon fiber a bit. Lessons learned for next time (probably a cutaway OM 12 fret).
- If God had intended us to drink beer, He would have given us stomachs. - David Daye.

- The mouth of a happy man is filled with beer. -

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Mark McLean
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Location: Sydney

Re: OO cutaway

Post by Mark McLean » Sat May 04, 2024 3:25 am

Looks great Joel. The knot on the neck is a perfect example of wabi-sabi and the art of appreciating the imperfection of materials (and the craftsman), and the impermanence of all creations. It is perfect by including that imperfection. What are you planning for number three? Come on, don’t pretend that you haven’t been thinking about it…….

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joel
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Joined: Thu Oct 11, 2007 7:55 pm
Location: Brisbane, Australia

Re: OO cutaway

Post by joel » Sat May 04, 2024 5:05 pm

Thanks Mark.

Thinking about number 3, and 4 and 5! Number 3 will be very similar to this one, but it'll be an OM size, 12 frets to the body, cut away. I'll hopefully build it better using the lessons learned from No.2. No. 4 and 5 will be 335 style electrics at this stage.
- If God had intended us to drink beer, He would have given us stomachs. - David Daye.

- The mouth of a happy man is filled with beer. -

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