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Thank Ratae and Kwak. I'll return to your comment in a minute.
While the top is flat I lay out the f-holes
I was planning to use a follower bit in my little router but didn't have one small enough so I'll just cut them by hand. The little red line is supposed to be a sighting line for the saber saw - doesn't work too well
Use the template to clean the hole up, I'll finalize it later (still haven't decide to bind the f-holes or not)
Great lessons, Freeman. It's always a fascinating read to hear one's thinking behind these little structural tricks. I can't wait to see how the decorative stuff comes out later on.
Might be a good time for some left brained lutherie. Most of this is pretty ordinary - I'm expecting problems with the cutaway and the floating fingerboard is new. But the main thing I've been thinking about lately is how to make the top work. Follow, if you will, my thought process.
First - what this is NOT. It's not an ES-175, which would have a laminated (yeah, plywood) top pressed into shape under tons of hydraulic pressure. Somewhere on the web there is a video tour of the Gibson plant where they show making this style top. The ES would have large braces in kind of a ladder form to support the pickups. As I have said before, this is not an ES-175
It is also not an archtop, altho it does take a few things from that type of instrument. A true archtop would have a top carved out of one thick block of spruce - both the outsides and inside is carved kind of like a shallow bowl. No matter how you make them (by hand, with a duplicator or cnc) there is a heck of a lot of hand work which partially explains why real archtops sell in the five figure range. Typically they have a simple X brace or sometimes just two little braces like this mandolin - the feet of the bridge sit over the brace and it helps dissipate the vibrations into the top
Also, it is not a pinned bridge flat top, altho again, I'll take a few things from that style bracing. Most steel string flattops use the Martin style X (you know I could talk about this stuff for hours but this is an electric forum). The bridge is under rotational forces from the string tension and wants to pull up in the lower bout and be forced down around the sound hole - the X is a very elegant way to counter these forces. Little braces called "tone bars" allow the builder to modify the stiffness of the top which has a dramatic affect on tone.
What I want to do here is get a bit more dome than a standard flat top. I want to support that with an X that is will help hold the shape as well as fit under the feet of the bridge to transmit vibration. I'm going to put a transverse brace in the upper bout, again to hold the shape but also because cracks can occur from the neck extension. I think I'll put a very small bridge patch in - not sure why, just seems like a good idea.
First cut some braces. How about 5/16 wide and 3/4 tall - remember that the strength (stiffness) of a beam (brace) is proportional to its width (make it twice as wide its twice as stiff) but proportional to the cube of height (make it twice as tall, it will be 8 times stiffer). Sand them to 15 foot radius (just happens I have that dish and it will make about the same dome as an ES-15
X marks the spot - glue them to the top against the 15 foot dish
Interesting. I see the similarities with your mandolin build. It kind of reminds me of a hollow body an uncle of mine once had. That was a very light instrument with an almost "nasal" unplugged tone. I wonder: have you ever played such a guitar?
I also see that you're using a radius dish. What's the radius? 12'? 16'?
2013 Official Luthier's Forum Medium Jumbo (Western red cedar/mahogany)
2012 McKnight McUke (soprano ukulele, redwood/mahogany)
2010 Martin D-16GT
2006 Larrivee OM-03R
1998 Fender American Standard Stratocaster (natural ash finish)
1989 Kramer Stryker
197? Epiphone Texan FT-160N
Set the top aside and glue the center reinforcing strip to the back. This is simply a piece of Spanish cedar cut with the grain going across the seam
And add the braces to the back. Simple standard ladder braces with a 15 foot radius
Note, I only have so many go-bars of each length so I put little wooden blocks under them to both distribute the clamping pressure and to adjust the length to whatever I'm trying to clamp. A go-bar deck can apply an amazing amount of clamping pressure.
I like the idea of arching the top more....given that this guitar is going to deal with downward bridge pressure and not the pull of a standard flat top. I see you used a maple bridge plate more in keeping with a flat-top's having to deal with metal ball end pins. I would have probably used spruce instead but no big deal. I would think, though, that bracing should follow an archtop's pattern more than flat-top just based on the task that soundboard is required to do.
An archtop guitar is usually braced less than a flattop because it is subject to less stress under load. This is basically because the strings don't anchor into the guitar face and some of the stress is carried by the tailpiece anchored to the box edge. The trap one could easily fall into is bracing this archtop like a flattop because the top isn't carved....when in reality it's functioning more like an archtop.
I would brace it a little more than a standard archtop because a truly carved spruce top is a little thicker than plates designed for flattop guitars. But not by much. You're basically bracing so that the top doesn't sink. Bracing at the edge not being that critical because the top is being pushed into the sides...not pulled away. I probably would crave all braces so they are nothing by the time they reach the kerfing. And just brace a tad heavier to compensate for the top plate being thinner than a truly carved archtop.
"I don't want to be immortalized through my work. I want to be immortalized by not dying." Woody Allen