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http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=13696		 Page 1 of 3
Author:  jonhfry [ Wed Sep 19, 2007 4:19 am ]
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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.

Author:  jonhfry [ Wed Sep 19, 2007 4:20 am ]
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edit


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

Author:  jonhfry [ Wed Sep 19, 2007 4:43 am ]
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Thanks,


That is exactly what I was planning on doing tonight, is making some patterns for various radii. Now I will do it correctly.
Author:  Michael Dale Payne [ Wed Sep 19, 2007 4:45 am ]
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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.
Author:  Michael Dale Payne [ Wed Sep 19, 2007 4:51 am ]
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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
Author:  Michael Dale Payne [ Wed Sep 19, 2007 4:59 am ]
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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?
Author:  KenH [ Wed Sep 19, 2007 5:05 am ]
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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'


 


 
Author:  WaddyThomson [ Wed Sep 19, 2007 5:05 am ]
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Yeah, I think Michael is right a 28' radius dish represents a sphere with a 56' cross section/diameter.
Author:  Rod True [ Wed Sep 19, 2007 5:06 am ]
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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.
Author:  Michael Dale Payne [ Wed Sep 19, 2007 5:07 am ]
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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
Author:  WaddyThomson [ Wed Sep 19, 2007 5:11 am ]
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Right!  Radius and diameter or cross section of a sphere cannot be confused.  That's why they call it a radius.
Author:  Michael Dale Payne [ Wed Sep 19, 2007 5:11 am ]
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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.
Author:  Rod True [ Wed Sep 19, 2007 5:11 am ]
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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.
Author:  KenH [ Wed Sep 19, 2007 5:14 am ]
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you are right... my bad
Author:  WaddyThomson [ Wed Sep 19, 2007 5:16 am ]
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It's OK, Ken.  You've been too busy to think about someone else's details.
Author:  Rod True [ Wed Sep 19, 2007 5:17 am ]
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Hey no worries Man

We're all just going round in circles here is all
Author:  Michael Dale Payne [ Wed Sep 19, 2007 5:18 am ]
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Good one Rod
Author:  Dave White [ Wed Sep 19, 2007 5:19 am ]
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[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.
Author:  Michael Dale Payne [ Wed Sep 19, 2007 5:19 am ]
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Here we go round in circles!
Author:  Michael Dale Payne [ Wed Sep 19, 2007 5:33 am ]
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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.

Author:  Rod True [ Wed Sep 19, 2007 5:37 am ]
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I was wondering if Dave would mention his tall tops

Thanks Dave
Author:  jonhfry [ Wed Sep 19, 2007 5:38 am ]
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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?


 
Author:  WaddyThomson [ Wed Sep 19, 2007 5:40 am ]
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In all of my ignorance and confusion  -  Yep!
Author:  Dave White [ Wed Sep 19, 2007 5:47 am ]
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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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