Three Random Questions

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AKEric
Gidgee
Posts: 2
Joined: Fri Sep 28, 2018 1:29 pm

Three Random Questions

Post by AKEric » Tue Oct 02, 2018 6:46 am

Hello, my name is Eric. I'm new to the forum, forgive me if this is tired subject matter.

I live in Anchorage Alaska and build purely for fun. I have two OM sized SS's completed, the first was under the supervision of Charles Fox at the American School of Lutherie. His class was a terrific experience, and he introduced us to The Books.

I've been digesting the books for a year and finally got started on my third guitar, another OM SS that will be 14 fret and falcate braced. I fully understand the reasoning for the 12 fret, I'm just not ready to go that route. Mainly because I'm not ready for a cut-a-way quite yet.

It took me a month or so of fiddling around to complete equ.'s 4.5-2,3,4,7, but I did prevail. This forum was very helpful, so thank you all very much. I think I've read every post at least once.

Down to my questions.

#1: Do these density, frequency and Gpascal values fall in line with others that use sitka? They are quite different from the Engelmann samples of the Design book. I'm using what I think is a very light piece of sitka spruce for the top. It is quartered quite well, has wide grain spacing and a small amount of bear claw. Tap tone is very good in my somewhat limited experience and comparing it to eight other sets I have:

a = 496mm
b = 389mm
m = 227g
v = 568 x 226 x 4.63mm
p = 382Kg/m3

fl = 75hz
fc = 155hz
flc = 55hz

El = 9.56Gpa
Ec = 1.04Gpa
Glc = 1.08Gpa

Target Thickness = 2.86mm or .112”

#2: See attached bracing plan. Because of the 14 fret design, I had to shift the falcate bracing pattern quite a bit. Following the falcate bracing criteria of Build page 7-11—especially item (e) requiring braces to divide the lower bout in equal angular segments—my side tertiary braces are not perpendicular to the guitar centerline, but at a rather large angle to it. They could be perpendicular if the inboard brace ends aren't placed under the front corner of the bridge, but that criteria seems important to me.

Will this placement of the tertiary braces adversely effect vibrational modes, and ultimately the sound of the guitar?

#3: I was taught to terminate the outer ends of braces so they feather to zero height just as they reach the lining so it appearers as if they disappear under the lining. I like this because it is simpler than housing the brace ends in the lining, it looks very slick, and the sound of the two guitars I've made is pleasing to me (it seems to work well). No carbon fiber was used.

This technique was used for all the back's ladder braces, the top's upper transverse brace and the upper ends of the X brace with seemingly no ill effects. The top's upper transverse brace is not quite as big as the falcate design at only ~6mm by 19mm (1/4” x 3/4”) in cross section and cathedraled to a sharp point. It seems that both of these aspects of the upper transverse brace are at odds with the very stout structure that is the falcate tradition. My head block is somewhat more robust, however, being made out of a single block with a substantial shelf and foot extending rearward for the top and back panels to glue to (see attached). It is also a bolt on/off design.

On this new one I plan on a live back and carbon on the top bracing per the falcate design.

So, my question is, does anyone have any thoughts on how brace ends should terminate? Is it primarily tradition to let them into the sides, or is there a good reason for it?

Sorry for all the rambling. This probably should be separated into three post, but here it is. Thanks for any help offered.

Eric
Attachments
DSC06686.jpg
Head Block
DSC06666.JPG
Falcate Bracing Plan

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Trevor Gore
Blackwood
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Joined: Mon Jun 20, 2011 8:11 pm

Re: Three Random Questions

Post by Trevor Gore » Wed Oct 03, 2018 11:14 am

AKEric wrote:
Tue Oct 02, 2018 6:46 am
#1: Do these density, frequency and Gpascal values fall in line with others that use sitka?
There's a saying that some of us are wont to use "Spruce is spruce", meaning that across all the various spruce species Young's modulus is proportional to density, irrespective of species. Your piece of Sitka falls well within the norms. If anything, it is a little dense for its Young's modulus when compared to my data.
AKEric wrote:
Tue Oct 02, 2018 6:46 am
#2: ... Will this placement of the tertiary braces adversely effect vibrational modes, and ultimately the sound of the guitar?
I doubt it.
AKEric wrote:
Tue Oct 02, 2018 6:46 am
#3: ...does anyone have any thoughts on how brace ends should terminate? Is it primarily tradition to let them into the sides, or is there a good reason for it?
As a general rule I let upper bout braces into the linings for better structural support and feather lower bout braces to nothing, short of the linings, so as not to lock up the motion of the top. You may find Al Carruth's post in this thread of interest.

johnparchem
Blackwood
Posts: 384
Joined: Mon Jan 21, 2013 2:59 am
Location: Seattle
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Re: Three Random Questions

Post by johnparchem » Wed Oct 03, 2018 1:32 pm

I built a falcate braced 14 fret to the body Martinish 00 on commission. The owner loves the sound and has recently bought a falcate brace classical guitar of mine as well. I like the the deep or more full bass sounds that I get from 12 fret joins. I tried to talk him into the 12 fret but all of his steel string guitars are 14 fret. He did take the classical with the 12 fret join.

Here is a complete build thread. http://harvestmoonguitars.com/Philip1.htm

AKEric
Gidgee
Posts: 2
Joined: Fri Sep 28, 2018 1:29 pm

Re: Three Random Questions

Post by AKEric » Thu Oct 04, 2018 1:56 am

Thank you Trevor and John. Much appreciated for your replies.

Eric

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