Official Luthiers Forum!

I've seen a lot of information regarding top and back radius but I've been unable to figure out how the radius' are determined. The first guitar I built had a 63' top and 20' back. I've yet to see another guitar that used 63' radius but a number that have used 20' backs. Is there a rule or guideline regarding top and back radius?

Well, I know a lot of builders as well as manufacturers use a 25-28 foot top radius as it corresponds well to a 1.5 degree neck angle.

As Ed Taylor mentions, the top radius does play into the neck angle somewhat. With that said, a lot of builders sand the radius out of the top where the fingerboard glues up.

I always figured the backs were radiused because they would look lousy if they were concave. Also, bowl sanding the radius into the sides is a great way to fit them up to the back for glue up.

_________________
http://www.PeakeGuitars.com

I know that extra strength is gained from the structural curved shape which should allow for less top bracing, but I do wonder, how a true flat top and flat back guitar would compare sound-wise arched ones.?
Ed

I have built some flat tops and they sound fine. I have lately been using a 28' cylindrical radius on the ribs and bending a flat top over them. Thinking of going to 25' or maybe even 20'. My backs are the common 15' dish.

Kevin Ryan believes they do ok. As do a number of very well respected builders, including many on this forum. Lots of ways to build these things.

_________________
Eagles may soar, but weasels don't get sucked into jet engines.

A true flat top becomes slightly dished in the lower bout under string tension. Over time a true flat has a greater tendoncy to become concave in the upper bout as the FB extention tends to rotate inward. this issue is one of the reasons that lead to the development of a domed top

Thanks for the responses so far. I am very curious though to find out if there is a rule of thumb that says something like "dreads have a 20' back and 28' top, 000 have 15' back and 25' top, etc. What do you guys use for most of your builds? I'll probably be buying some dishes and would like to have a general feeling as to common practices before I shell out $$$ for dishes I won't be using

Thanks!

Mike, there is no "rule", more just standards as set mostly be Martin Guitars. That is the 25/28' top, 15' back. On classicals it is more like 30' and 20' or so back. Having said that I have made dishes for people that range from 10' to 60'. It is just one part of the 'system' and what ever you choose, you just have to consider that for the rest of your build. Some makers are actually reverse neck sets now, that is the neck shifts forward, so again, there are standards but no absolutes and none are "righter" than the other, IMHO.

Shane

_________________
Canada

Mike ;
You have been given allot of good advise here.

We all have to find what works for us as makers of instruments .
Shane is correct that Martin set the norm -BUT many have found that a different radius for top or back gets the tone we're after.

Shane's radius dishes are the best I've found and priced right.

Find a guitar you like the sound of and measure the radii of the top & back.
Then make a copy of it .
If you like the tone (sound) then you've made the first step towards finding the radii you want & need .

Mike

_________________
Mike Collins

You should see them now Mikey! Now that I have the collets you sent I do them on the cnc machine and they are just that much more accurate. I am a HAPPY GUY!!

Thanks again for your help!

Shane

_________________
Canada

Yo, Jag

Standards, rules of tumb ect...well they don't. exist in luthierizem unless of course you work on an assembly line in one of the guitar factories.

A lot of beginners follow the "standards" set "buy from the big guys" and well me ain't never seen two people alike just like me never seen two guitars alike...even consecutive serial numbers off of the assembly line.

The various dudes on here have given you the reasons for this type or that type of top or back shape and bracing...all very good factual information and reasons for.

but this is the Padma and well my approach is a little some what different...and that is....me don't give a hoot what the assembly lines spew out or what master official luthier Joe Blow bends, carves, arcs or dishes out plates to, or if he or she holds the sucker together with spit a chewwy gum or bondo, bailing wire and duck tape.

What does interest me is ... how you wanna do it. Your originality, your creative contribution, no matter how large or small. Did you have fun doing it? How does it sound and what you think would make the next one sound different or "better", whatever better is.

These things are extremely personal and amount to growth of the individual.

So you have a choice here...follow the dictates of the big boys and buy your ax in pieces from one of the dealers listed up above (all really good products) and spew out another copy of a copy of a copy, or
simply just start building to please yourself and maybe find a whole new person inside while doing it.

In reality it matters not the choice that is made on a 15 ft or a 16 ft radius dish or if you used Joes finish or Bills finish...do you really think that the radius on the back is gonna matter when your dead and gone and the axe you built is trashed or in a museum? No. What really matters...in MHO is

finding out whats your blis and then following it.


blessings
the
Padma


PS

Of course if you need to lay some bucks down on a dish, well then you need the Padmas one size fits all, supper duper guitar radius dish....just slip $20 in to an envelop and send it to "the Padma" C/O this here web site. Sorry, NO CODs or Credit cards!

_________________
.

Audiences and dispensations on Thursdays ~ by appointment only.


.

I'd also suggest looking at the domes of more radical makers like Stefan Sobell, and our own Dave White who I know uses 13' tops and 10' backs and they really project and yet still have good bass I've used them on a lightly braced uke and was very impressed with the results I think they rely on a heavy bridge too or that's my impression

_________________
Formerly JJH

I learn more from my mistakes than my successes