Official Luthiers Forum!

I have been thinking about this issue for a good long time and with Hesh's recent post in the Tute section I thought this discussion may be timely.

I know that there are a few people that use a similiar method to John Hall and Hesh where the upper portion of the guitar is built flat and the lower section is radiused (in Classical construction it is similiar with the solera dished only in the bridge area). I am wondering why this is done (for steel strings, classicals are different animal in my mind!) and or necessary. My thoughts are to build the entire top domed (pick your radius, 25', 28', 30', 45', 60', whatever), sand the rims with your dish and glue the top on. Then with a flat block just flatten out the area where the fretboard sits. Why does the whole upper bought need to be flattened? I think that the process I just presented (and I know is used by lots af makers as well) is just easier and keeps all stresses equal. When we talk about flattening out for the fretboard we are talking about a small area (2.25 inches wide or so) and the actual radius that needs to be removed is almost nothing, even at a 25' radius.

Looking forward to some discussion and thoughts on this.

Thanks

Shane

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Canada

Shane,
I had wondered about the best way to deal with that as well. What I really like is Taylor's approach of having a fully domed top, and routing (CNC'ing in Taylor's case) a very shallow pocket for the fretboard into the top. I must confess though that I have not spent much time into thinking about how to implement that idea as a hand builder.

http://www.taylorguitars.com/guitars/features/ntneck/Features.aspx

Christian

As an inexperienced builder I was wondering if anyone has built with 25' radius top, with flat upper brace, glued to a flat rim.
I'm thinking of trying that for next build, and wondered if anyone else has actually done it?

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Ignore last post - this is talked about on another thread - "Please help with possible mistake!!"

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I have done it two different ways;

1. All braces and rims radiused at 28'

2. All braces except UTB radiused, and rims radiused below sound hole, and flat above sound hole at the proper angle for correct neck geometry.

Both ways worked fine for me. It probably took a little more time on the second method, but not much.
As far as flattening the top at the fingerboard extension area on the 1st method, you could hollow out the underneath of the fingerboard in the center area to fit instead. That is if you are concerned about weakening the top.

Chuck

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Your braces will tell you what you need to do. I use a Martin style and they flatten the upper bout. With a 1 1/2 degree neck angle and 28 foot top radius as I do them , the flat works best for a straight transition area for the fret board.
If you use a full domed tops there is actually a slight curve on the fret board extension, after all you have taken a convex dish and sanded the rim and if you also sand the braces you have the dome .
I don't think it is big issue just a difference in techniques. So as a rule of thumb , if you have a flat transverse brace do the flat , if the brace is radiused don't flatten.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Shane, I had assumed one would be concerned about the length of the fretboard extension instead of the width (roughly 3.3" from 14th fret to 20th fret on a Martin long scale). Still, not a lot of sanding.

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Formerly known as Adaboy.......

I guess Darryl one would be concerned in both directions. John Hall has summarized my thoughts on this issue well, either works fine and it is whatever makes most sense to you. One of the reasons I brought up this topic is because I am often get asked about dealing with this area of the guitar by people buying radius dishes. I have NO concerns about thinning the top in this area as the amount that needs to be removed is quite small and it is being replaced by .25" of ebony. Also, adjusting braces to an 'A' style into the neck block adds a lot more stability in this area as well but even 'conventional' bracing poses no issues with either method.

Thanks all for your comments....

Shane

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Canada

For my next build I am actually thinking to go the opposite route - fully domed top, trussed neck block, and fretboard extension floating above the top (i.e. not touching the top at all).

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The member formerly known as erikbojerik....

I have built both methods. I prefer the one with it flat above the UTB. It is faster for me and because I build with thin tops - around 0.080", I'd rather not sand any more off the top.

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

I don't sand off the top , I think this is not a good practice . I do like Martin and create that angle in the side set itself. I can't see sanding off wood in an area that you want to keep as strong as possible. I have a good video on this to show how to do this on YouTube. Look for the bending video #3.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I've been using a cylindrical radius across the grain and flat with the length. Works great.

I leave the top area above the upper bout a little thicker and use a patch with tapered sides under the bridge extension instead of a popsicle brace. That keeps the area strong even if it gets a little thinner after sanding it flat.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

Thanks Ken,

I like that idea! That would help resist the cracking often seen in the top that follows along the side of the fretboard extension. And if a person glued those patches so that the grain was a little askew of the grain of the top it would be even stronger.

Shane

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Canada

Shane, the grain of the patch is at a right angle to the top grain, similar to the bridge plate.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com