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Top and Back Radius
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=17047		 Page 1 of 1
Author:  Conspiracy [ Fri May 02, 2008 12:06 pm ]
Post subject:  Top and Back Radius
First I should introduce myself. I've been lurking for a little while and this is a great forum. I'm an engineer by day, poor guitar player by evening, and woodworker on the weekends. I've thought about building my own guitar for a long time but I must admit that reading SteveS's building threads over on AGF a year or so ago is what really inspired me to make the leap. I recently purchased the Cumpiano book and I'm currently reading through it but I already have a question.

This weekend I'm going to start building some jigs and I've read here and other places about radius dishes. So far as I can tell Cumpiano, in the book anyway, doesn't use one. It seems to me that using a dish would make several things a lot easier so I'm going to go that route. The issue I'm having is that there are several "standard" radii. I've searched but I can't seem to find any discussion on the merits of a given radius. Why would someone use a 28' vs. a 15' (or a 20' or a whatever')?

-Jim Wick
Author:  Hesh [ Fri May 02, 2008 12:15 pm ]
Post subject:  Re: Top and Back Radius
Hi Jim and welcome to the OLF! [:Y:] [clap] [clap] [clap]

There is no such thing as a standard radius for guitar building. Various builders will use what ever they wish for what ever reasons that they determine.

I use 15' for backs and 25' for tops and this has worked well for me for dreads, OM, L-00s and SJs. 15' and 25' respectively seem to be pretty commonplace though and many of use these.

Since you are considering building your own dishes any radius that you wish is available to you.

Welcome aboard!
Author:  Darren W [ Fri May 02, 2008 12:29 pm ]
Post subject:  Re: Top and Back Radius
Hi Jim,
Welcome! SteveS is a fantastic fella and builds a very nice guitar as well; he inspired me at a local AGF get together about a year ago. To my limited knowledge, there are some subtle tone changes when you get to the extremes in the back and top radius, but that most people using 15-30' domes aren't going to be able to detect noticable tonal differences with all other things equal. Aside from how the fingerboard will glue onto the top without a bump resulting from the radius of the top, I think at least for us newbs which radii the top and back will be are not hugely consequential. Their main funciton is to resist problems later on due to humidity changes. But you may want to hit up Tracy at Luthiers suppliers. These things are evidently no fun to make yourself... big mess.
BTW, I use a 28' top and a 16' back.
P.S. It's been a while since I was in Folsom. Do they still have Pizzaria Classico downtown? I miss those garlic chips!
Author:  Frank Aarre [ Fri May 02, 2008 12:37 pm ]
Post subject:  Re: Top and Back Radius
I've been wondering this exact same thing.

I think i read somewhere that using a 28' radius helps to line things up with the neck angle. (don't have any building experience myself yet, though)

I'm going to make my own bowls out of mdf. should be quite easy to just cut some guides for the router with the proper radii. btw. i'm going to use 28&15 on mine.
Author:  Guest [ Fri May 02, 2008 2:01 pm ]
Post subject:  Re: Top and Back Radius
Cumpiano at the time T&T was written free form built, as did not use mold or dishes. he hand shaped the arch in the braces and the braces cause the top and back plates to conform when glued up.
Author:  Alain Lambert [ Fri May 02, 2008 2:11 pm ]
Post subject:  Re: Top and Back Radius
Hi Jim, welcome to the OLF.
You should go to the Cumpiano site
http://www.cumpiano.com/Home/Book/textbook.html
for update on the book. Especially the neck joint, radius dish, and so on.


I use 28 for top and 20 for back
Good luck!
Author:  Ken Franklin [ Fri May 02, 2008 6:34 pm ]
Post subject:  Re: Top and Back Radius
I use 30 for the top and 18 for the back. Binding is certainly easier with less radius.
Author:  Conspiracy [ Sat May 03, 2008 3:29 am ]
Post subject:  Re: Top and Back Radius
Thanks for the warm welcome everyone.

Hesh wrote:
Various builders will use what ever they wish for what ever reasons that they determine.

For me this is the crux of the matter. I have no reason for any particular radius. I suppose through experience I would form a bias but currently idunno

So some others are doing 30 and 18, others 28 and 20, 28 and 15, etc. It's difficult for my engineer side ( :ugeek: ) to do something arbitrarily. The thought of easier binding routes and neck mating greatly appeal to me. Perhaps the range of values has just been empirically derived? Over 30 perhaps you may as well go flat? Under 15' it's too noticeable?

Darren W wrote:
But you may want to hit up Tracy at Luthiers suppliers. These things are evidently no fun to make yourself... big mess.

I've thought about buying them but I found a pretty slick and I think easy way to make 'em: http://www.mcguitars.com.au/forum/viewtopic.php?t=231. I was going to go with smaller width and pie shaped for the sub-dish pieces. Anyone have any thoughts on what I'll call the Down Under Dish? Maybe I should start a new topic for this one.

Darren W wrote:
P.S. It's been a while since I was in Folsom. Do they still have Pizzaria Classico downtown? I miss those garlic chips!

Yeah it's still there and the garlic chips are still good! You've got some good eats down in SD too. My Grandma lives in La Jolla and my brother is out in Scripps Ranch (the fire was less than a mile from his house). Whenever I'm down there I grab some fish tacos.

Alain Lambert wrote:
You should go to the Cumpiano site...
http://www.cumpiano.com/Home/Book/textbook.html
for update on the book. Especially the neck joint, radius dish, and so on.

Good tip. I went there but I didn't see a radius dish mentioned.


Again, thanks everybody for making the new guy feel welcome!
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