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I'm considering building a grand auditorium with florentine cutaway and I'm trying to decide how deep my cutaway should be. To make it deep I'd probably need to skew my upper transverse brace a little as in this drawing. Without the slight "displacement" of the UTB, the cutaway would seem to be quite shallow, which might be okay for venetion, but a florentine seems like it should be deeper. Any thoughts on the matter...

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Why don't you just put the UTB where you want it and have it terminate at the cutaway wherever it lands. I know this is a bit "apples to oranges" but that is how I braced the flattop mando with Florentine cutaway I did for the challenge here a few years ago (there should be a picture in there somewhere). Maybe there is a reason I shouldn't have but I was too naive to know. Anyway, it seems to be holding up just fine.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I like Simon Fay's design where the UTB is cut from a larger piece of hardwood so it curves around the cutaway.

But even more, I like 12 frets Soundhole down lower so there's plenty of room.

Steve, to be honest, I haven't done one myself, but I've seen others where the UTB is angled to no ill effect. The only one I can name for sure is Grit Laskin.

Good luck

Steve

I just saw this photo on LMI's website. It shows who ever shot the photo skewed the UTB and terminated the brace at the cutaway. Helps to give me ideas...

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Remember to account for the total thickness of the side + kerfing.

I just measured, and my upper transverse is 3 9/16" from the neck joint. The deepest part of the cutaway is 3 5/16".

Just make sure it isn't so deep that causing the rosette and purfling to overlap.

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I do what Brian does and end the brace at the cutaway. What you've drawn looks good to my inexperience eye.
Just please don't make it semicircular!

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"I am always doing that which I cannot do, in order that I may learn how to do it."
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I saw this on another forum about a CF100 restore

You do not want:


Because:

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http://www.Harvestmoonguitars.com

The CF-100 that is being restored is the one I am doing. If you like I am also documenting it here at the OLF in the Restoration section but with less detail than over at Luthiercom.org. Over there I started another thread called "What's Wrong With This Bracing" and we discuss the issue and look for better ways to do it. I am restoring this CF-100 and I don't want to make any drastic changes from the original so I am limiting how I fix the problem.

This guitar was only made from 1950 to 59 an there were only 1500 or so made. It was also the only flat top with a cutaway that Gibson ever made so that probably tells you that it is a bit of an unstable design. I can say what I have found out is that the angled UTB along with the deep cutaway causes the neck to twist as it comes up. The side of the cutaway acts as a pivot so instead of the fretboard extension wanting to moves straight down it also twists. Compounded with the fact they didn't tuck the UTB under the lining but just butted it up against the upper part of the X-brace this was a recipe for failure.

I am working on the best fix for this problem and still keep the guitar as original looking as possible so moving the sound hole down is out of the question. But that would be my best guess on how to build one from scratch. If you have enough room to run the UTB straight across and avoid the Upper X-brace it would be like a regular guitar but you would have to beef up the side where the cutaway is (deeper Heel block). Another option is to half lap the UTB and the X-brace which is what I am looking at right now.

Here is a drawing I am working up in CAD to look at ways of fixing it.

Cheers,
Bob

Maybe this can help you in your quest.

A reverse double X...

Cheers,
Bob

Bob - Thanks for that info. Interesting about the twisting. Since it looks likes my design will allow my planned cutaway depth with only a slight skew of the UTB, nothing to drastic, I think I should be okay. I'll still have room between the upper x brace and the UTB. ...and I will be tucking them of course.

Peter - I'm not planning on this cutaway to be semicircular, but here is an OM with a semicircular cutaway that seemed to work pretty good. Do you not like semicircular cutaways?

BTW - The UTB stayed in the usual location for this one.

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Steve,
Actually I think the skewing is caused more by the cutaway than the UTB although slanting that does contribute to it. If you had a chance to look at the thread I am doing on the restore of this CF-100 you will have seen that I had to replace the soundboard. Once that was removed the back and sides lost all support. So I had to make a jig to square the body up and set the neck angle. In thread I explain how the neck angle was skewed left to right. I temporary shimmed the dovetail so I could find out where the angle should be. By just moving the neck up and down I can see that it also moves left to right just because of the cutaway. Because the heel block is attached on one side (the cutaway) and not the other, any movement will skew the neck back and forth.

I have learned a lot about the geometry of how a cutaway in doing this restore. So I would suggest if you want this guitar to last a long time you should give some serious thought about the movements involved. Since you are building this one it may be worth your time to take the sides and back out of the mould (if you use one) and actually take a look at the movement you get with no top on the box. It will give you a much better Idea of the stresses you need to combat with the bracing.

Just food for thought...

Cheers,
Bob

P.S. I think if I were building one from scratch I personally would look further into the last drawing I posted here with the reverse double X.

Sorry it's just a pet peeve of mine. I was talking about this sort of thing. I really don't like that look:
http://www.guitar-museum.com/uploads/gu ... 8711-2.jpg

But thats just my opinion!

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"I am always doing that which I cannot do, in order that I may learn how to do it."
Pablo Picasso

https://www.facebook.com/FenskeGuitars

Bob - You're scaring me... You said that you think the twisting is more due to the cutaway than the location of the UTB. In the case of the CF-100 where the UTB is simply butted up against the x-brace, no wonder that would cause issues. I guess that the typical Florentine is deeper than the typical venetian. Seems like there are many, many cutaways out there that haven't experienced the twisting you refer to. Not that I am taking issue with your assessment.

You mentioned that the fact that the heel block is "attached" (glued) on the cutaway side but not the other could be a contributing factor. What if a smaller support "block" was glued in the corner of the heel block and the side opposite to the cutaway? Do you think that would help shore up and stabilize the neck joint and help prevent the twisting?

BTW - I always thought the CF-100 was a cool guitar... Your work on it is impressive.

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Steve,
I didn't mean to scare you about doing a cutaway. I was never really aware of any of this until I saw the amount of damage on the CF-100. In part it was due to the previous repair which didn't repair the problem which was loose braces. By not repairing the braces it allowed the heel block to twist and make things even worse. Funny because the neck joint held up great and was very tight with no gaps between the body and the neck. It was just everything else that let go.

So I didn't mean to scare you but just make you aware of the forces involved. In the thread I talked about earlier someone suggested to extend the heel block to compensate for the twisting and I think that would probably take care of the issue. Someone else suggested bracing from the sound hole up to the heel block which led to the idea of the reverse double X bracing that I posted above.

The issue I have it because the CF-100 has such a deep cutaway and the fact I want to keep this as original as possible.

Yes, there are a lot of guitars with cutaways that do not have this issue but it is good to be aware of it if you are building one.



Yes, I think this is one of the coolest guitars made. And thank you for the compliment on my work on it.

Cheers,
Bob

I think Jackson Browne has about 25 of them...

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Of course, whatever approach you use to locate the UTB, just remember you also have back braces that need to clear the cutaway, otherwise you'll find yourself knocking off a brace and redoing it. Ask what I've been doing this afternoon!


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I'm not sure how much it moves the UTB (but obviously a fair amount), but the prettiest florentine cutaway, to my eyes, is Somogyi's. It just looks right to me.

In contrast, the ones like the 'LMI' picture you found above, with a tight circle and the point ending up in the narrowing portion of the bout, look really out of proportion to me.

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Jim Kirby
kirby@udel.edu

To make sure I had enough support for my relatively deep florentine cutaway I put in two UTBs. I feel pretty confident that the upper bout is braced sufficiently now...

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Looks pretty sollod to me.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Thanks Jay. I think so too...

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

I've always used two large braces in the upper bout. Cut away or not. My cutaway isn't as deep as this though so I can just run my braces perpendicular to the center line.

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I wonder how well a (laminated) brace formed into a shallow arc to clear the cut away would work?