radius dishes?

[edlee]

Hi again everyone. I just started lurking around the forum and have a ton of questions if you all don't mind. I was wondering what the purpose of a radius board has when bracing your tops and bottoms? How do they work? Do you sand a radius into your braces and place them onto your tops or bottoms? What effect dose this have on the sound if any and why do you want your guitar to have a radius? Do you want more of a radius in your top or bottom or both the same radius? Also what about depth? Does depth have an effect along with the radius or is depth one subject and the radius is another subject? Thanks for all your help.

[Ron Wisdom]

Well, I use 15' radius for the back and 28' for the top. Arching the top and back adds strength and allows for movement with changes in humidity without splitting the wood (hopefully).

I use the dish to:

sand the curve on the braces

keep the back/top at proper curvature while gluing the braces on.

sand the radius onto the sides/kerfing so top/back will fit perfectly.

support the back while I glue on the top and support the top while I glue
on the back.

All my gluing and bracing is done in a go-bar deck, so this method works very well for using the radius dish. My dishes are double sided, made from two layers of 3/4" MDF. One side is just smooth, the other side has sandpaper. One double sided dish for 15' and another for the 28'.

Ron

[Allen]

I would use the term radius to describe the "dome" that is built into the top and back, also the fingerboard will have a radius built into it from High E to Low E on a steel string. I haven't built a classical guitar, but I hear that they use a flat fret board.

I would use the term depth to describe the dimension of the body, usually measured at the base of the guitar (the deepest) and the neck (the shallowest)

There are all kinds of reasons to build with a radiused top and back, and certainly one of the most important is to help allow the large expanse of wood to move in humidity fluctuations in a somewhat predictable manner. If you have to live and build in an area like I have to, this is a huge consideration. There are all kinds of other things that building with a domed top and back do, including helping to shape the tone of the instrument, strengthening the structure to list just a few.


[edited to correct wrong radius]
I use a 25' radius for tops, and 15' for backs, for no other reason than that is what I heard was the norm when I first started out and that is what I built my radius dishes at.

For an excellent tutorial on how to build a radius dish see Graham McDonald's article. Wish I had seen it before I built mine.

http://www.mcguitars.com.au/forum/viewtopic.php?t=231

[Ron Wisdom]

I use a 15' radius for tops, and 25' for backs, for no other reason than that is what I heard was the norm when I first started out and that is what I built my radius dishes at.


http://www.mcguitars.com.au/forum/viewtopic.php?t=231

Allen, aren't those bassackwards, or is it me?

Ron

[Allen]

No, it's not just you...just me

[edlee]

Thank you very much for the input and info everyone. Is there any litature that can obtained that goes into detail about the different uses for the radius and how certain radius designs have an effect on the guitar? It seems that there is a lot more to building a quality instrument than making a box. I have the Campiano book already, but it doesn't go into depth about if you do a certain thing to the design it will do this or that. If there is any info like that out there where can one look? Thanks again everyone.

[Alain]

Edlee, I think Ron nailed about every good reason to use the dishes. I will say that mine are probably one of the best tools that I have and they improved my building ten fold. The facility you'll have in sanding the rims and end blocks, plus using them to profile your braces are well worth the price if you buy them new. If you manage to make them yourself, all the better.

As for different radii acting in certain ways... I'll just say that there are so many factors that will contribute to the tone, voice and sustain of your instrument, I'd just say pick two (radii) and run with it. I seriously doubt that someone will strum your guitar and say, 'Oh, I see you used a 30' radius for the top and a 15 for the back... Which are the two I use, just in case you were curious.

However, there are certain builders that do not arch their tops at all... I think Olson is one of the most famous who does this (but I might be wrong).

Hope this helps,

Cheers,