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I have braced my back with a fifteen foot radius on the braces which seems to be fairly common from what I have read. My question is, do I also need to do the same lengthwise to make a true dome? 

Thanks in advance,

Craig.

Morning Craig,
Yes, but this is done by sanding a 15' radius in to the rims.
Do you have a radius dish?

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Lance@LuthiersForum.com

Yes the norm is as Lance says to just sand the rim to a 15' radius and the back should form a dome when you glue it down.

Many of us though are now using an X-brace on the back as well which will hold the back to better dome without the added stresses of relying on the glue bond with the rim.



This gives you the idea.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

http://www.bluescreekguitars.com/tutorial12.php
This link can show you the dome and how I attain it. The back will be radiused so the the dome would in effect act like a portion of a sphere.
    The link will explain it more than I can here.
hope that helps
john
blues creek guitars

I dont mean to hijack the thread, but has anyone radiused the top and the back to the same radius?  I have been thinking about trying a guitar with both the top and back both radiused to a 16' raqdius just to see what the difference is.

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Reguards,

Ken H

Thank you gentlemen for your help. This is my first instrument so I am working with pretty much the most basic of tools and equipment. I am building jigs as needed but to answer your question Lance I do not have a radius dish. I think it will be very difficult to get a good continuous bond to the sides without it so might have to put it on the list of essentials.

I really appreciate this forum and everyone's willingness to share their experience and ideas . I hope to be able to contribute myself as time goes on.

Thanks again

Craig. 

Welcome Craig,

I am also new to building. This forum is a great resource as well as Stew mac web site and blue creek guitar's web site which both are sponsors on this forum. You may want to search for blogs as well as look for a couple books  Kinkead and Cumpiano are pretty good for starters.

Peter

You don’t absolutely need a radius dish to shape the contour of the sides to fit the dome of the back or the top for that matter, although it seems to be the most common practice these days; I use dishes too, and I think they are helpful, so thank you Charles Fox!. The radius dishes are a relative new “invention” and guitars with radiused braces were made without the aid of dishes for years. If you study the book by Cumpiano mentioned previously, you will see a method of shaping the sides with a flat sanding board, and I believe the Kinkead book shows how you can shape them with a curved sanding stick. Cumpianos method will give you a slightly different geometry as a result than a “true dome” which some builders actually prefer.

The top can be dealt with similarly, with different resulting geometries and more importantly differences in sound. As an example, Huss and Dalton makes a “traditional” Dreadnought guitar where the sides are sanded flat before a top with radiused braces are glued to it, and a “contemporary” Dreadnought where the sides are sanded with a radiused dish before the top is glued to it. The top braces on both guitars are the same, but according to David Berkowitz who wrote about this in a thread which can be found in the MIMF library, there is a distinct difference in sound between the models. David wrote “…I suggest you listen to them before coming to any conclusions off the cuff. I've visited the factory and can tell you that the tops are braced the same. It's a remarkable and interesting difference.” I am not sure what the difference in sound between a "true domed" back and one made per Cumpiano's method is, I will say that both methods work well.

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Rian Gitar og Mandolin

[QUOTE=Hodges_Guitars] I dont mean to hijack the thread, but has anyone radiused the top and the back to the same radius?  I have been thinking about trying a guitar with both the top and back both radiused to a 16' raqdius just to see what the difference is.[/QUOTE]

Depending on what radius you use this can dramatically affect the neck angle and the over the bridge dimension of the fretboard plane. If a smaller radius is use it may cause an issue with sting clearance at the apex of the dome dependent on the scale length and dome radius.

[QUOTE=Hodges_Guitars] I dont mean to hijack the thread, but has anyone radiused the top and the back to the same radius?  I have been thinking about trying a guitar with both the top and back both radiused to a 16' raqdius just to see what the difference is.[/QUOTE]

Ken,

The tops on all of my instruments have the bottom of the braces radiused to 13' - my back braces are done to a 10' radius.

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Dave White
De Faoite Stringed Instruments
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