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The radii that I have used to make my dishes was based out of cumpiano's book. To achieve the arch what I did was made 3 points 24 on a 24 inch diameter and moved the middle point 1/4 and 1/8" lower, then extended metal rod and traced a line.

Just out of curiosity when we say a 14' radius, are we referring to an actual 14' radius, which would imply 'the radius of a 28 foot circle,' or are do we mean the radius of a 14' circle (which would actually mean a 7' radius)

sorry, the only stupid question is one I don't ask, and I am going to be making a jig for radiusing my fret boards tonight and want to be crystal clear on everything before I start.

edit

i meant 3 points on a line and moved the middle point

Thanks,

That is exactly what I was planning on doing tonight, is making some patterns for various radii. Now I will do it correctly.

Wow!!!!!! Either I have done it wrong for nearly 9 years or something is wrong but a 28' (336") radius dish has a 28' radii dome. that is a .2144" recess in the dish. A 15' (180") radius dish has a .4004" recess.

Every dish I have ever bought or built had the radii as stated. 15' dish had a .4004 recess at the center of the cord (center of the dish) based off of 24" long cord length

Maybe I am miss reading the statement here but 28' is the typical but by no means standard top dome radius. That dome when measured in a full spherical diameter would be 56'in diameter. If you in part a 14' radial dome (28' spherical diameter) into a top you will have a top that has a cord rise of .4288" over a 24" span. That is a huge rise for a top. in my opinion.

Am I missing something in the statement Hesh?

I believe Hesh has it right... a 28' radius is actually the arc of a 28' circle. the radius length would be 1/2 of that diameter, or 14'

 

 

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Reguards,

Ken H

Yeah, I think Michael is right a 28' radius dish represents a sphere with a 56' cross section/diameter.

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Waddy

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Michael's you are saying the same thing as Hesh and John.

John is saying that a 14' radius is the radius (1/2 diameter) of a 28' circle. I think you may have gotten caught up in the 28' statement and thought John was talking about a 28' dish, not a 14' dish.

I think John is wanting to make a 14' radius dish for his backs.

John your right in your initial thinking. The 14' Radius is 1/2 the diameter of a 28' circle.

Now before Howard jumps in here to correct us, we know we are talking about sphere's here and not just an arch, but it's considerably more simple to talk about it from a 2D point of view versus a 3D point of view.

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[QUOTE=Hodges_Guitars]

I believe Hesh has it right... a 28' radius is actually the arc of a 28' circle. the radius length would be 1/2 of that diameter, or 14'

 

 

[/QUOTE]

a 28' radius can not be actually a 28' diameter. A 28' radius can only be a 56' diameter

Right!  Radius and diameter or cross section of a sphere cannot be confused.  That's why they call it a radius.

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see that what I thought at first that the 14' radius was just an example of the question. but at the same time I was considering the fact that most tops have either a 25' or 28' radius dome. and I did not want to lead anyone into the impression that when we say we have a 28' radius top that we really mean we have a 28' diameter top.

Sorry Ken, but what you've said here is incorrect

[quote=Hodges_Guitars]a 28' radius is actually the arc of a 28' circle.[/quote]

A 28' radius would be the arc or a 56' circle, not a 28' circle.

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you are right... my bad

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Reguards,

Ken H

It's OK, Ken.  You've been too busy to think about someone else's details.

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Waddy

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Hey no worries Man

We're all just going round in circles here is all

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"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Good one Rod

[QUOTE=MichaelP] see that what I thought at first that the 14' radius was just an example of the question. but at the same time I was considering the fact that most tops have either a 25' or 28' radius dome. and I did not want to lead anyone into the impression that when we say we have a 28' radius top that we really mean we have a 28' diameter top.[/QUOTE]

The braces on my tops are shaped with a 26' diameter.

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Dave White
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". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Here we go round in circles!

Not that it is a problem but as compared to me you have very tall tops 26'(312") diameter dome would be 156" radius. over the length of a 20" cord (the nominal guitar body length.) that would be a .321" rise from the furthest perimeter to the center of the dome. That is nearly as much as my backs rise.

I was wondering if Dave would mention his tall tops

Thanks Dave

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"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

I think it is just confusion in my wording.

What I am asking is this:
I am making a simple fret board radiusing jig tonight. The neck end will have 14 foot radius and the other end 20 foot radius. So to make arches, I am assuming if I use the string/wire method like hesh to make my arches, I would stretch the string tight at 14 and 20 feet, right? (as opposed to 7 and 10 feet)

Does that make more sense?

 

In all of my ignorance and confusion  -  Yep!

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Michael,

No wonder my right hand gets so dizzy when I play

It would be like your diagram IF I had 13' radiused braces just about everywhere on the top AND I used a 13' radius dish to sand the sides and fit the top . . . but I don't. It certainly does that laterally - but over a 16" arc (or 9-10" in the upper bout) it is not as dramatic. Length-ways, most of the "fall off" on my guitars happens from the back of the soundhole to the tail-block - which helps me with neck set and bridge geometry, plus the saddle is angled back slightly in relation to the plane of the strings.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010