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  #16  
Old 09-28-2014, 05:31 PM
Trevor Gore Trevor Gore is offline
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I used to do compound radius boards and built a router contraption to do that. There is also analysis in the book (Appendix II.3) for "conical" boards, although any swept line will give you "flat" string lines which means the geometry can be pretty arbitrary.

However, once above ~16" fretboard radius, which is mostly what I build these days, the difference between a compound board and a cylindrical board is so small that it is easily buried in manufacturing tolerance, relief, drop-off, cold creep and seasonal movement. I've found that there's not much point to compound radius boards if the nut radius is greater than 16" and only do them (on request) if the nut radius is to be 10" or less.

There was a good article in American Lutherie maybe about 3 years ago called something like, "...cylinders almost do it..." which discussed the pros and cons of various surface geometries and came to much the same conclusions.
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  #17  
Old 09-28-2014, 08:30 PM
Frank Ford Frank Ford is offline
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If you're planning to do this by hand, why all the analysis?

What's to prevent you from installing the neck, fingerboard and all, and doing the entire job in situ?

Starting with a flat fingerboard, you can begin planing the radius and straightening everything up all in one operation, using a nice sharp jack plane.

Testing the radius at the nut from time to time with a contour gauge, and checking it up over the body, you can come up with a nice compound radius that will do the job very well. After you've approximated the contour, you can true things up and create the appropriate drop off over the body by sanding with a flat block. In my case, that would be the same 14" jack plane, used as a sanding block.

It's a system that has worked for me starting with my first guitar in 1969, and it's still the one and only method I use.
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  #18  
Old 12-02-2017, 11:07 PM
bausin bausin is offline
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>> I would appreciate any comment on the method I used to arrive at the two radiuses.

Murray,

To calculate the radius at the bridge, you will need to know the string spacings at the nut and bridge, the radius at the nut, and the scale length. The width of the fretboard is irrelevant.
To calculate the radius at the end of the neck, you will also need to know the distance from the nut to the end of the neck.

If you post those numbers, I can calculate the radii for you.

Steve

Last edited by bausin; 12-03-2017 at 12:14 AM.
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  #19  
Old 12-03-2017, 02:11 AM
LouieAtienza LouieAtienza is offline
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Quote:
Originally Posted by bausin View Post
>> I would appreciate any comment on the method I used to arrive at the two radiuses.

Murray,

To calculate the radius at the bridge, you will need to know the string spacings at the nut and bridge, the radius at the nut, and the scale length. The width of the fretboard is irrelevant.
To calculate the radius at the end of the neck, you will also need to know the distance from the nut to the end of the neck.

If you post those numbers, I can calculate the radii for you.

Steve
You only need know the radius at nut and 12th fret, nothing else. Whatever the difference in radius between 12th fre and nut should be the difference between bridge and 12th fret.

A fretboard with constant center and edge thickness cannot be a conical section...
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  #20  
Old 12-03-2017, 02:15 AM
LouieAtienza LouieAtienza is offline
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Quote:
Originally Posted by Trevor Gore View Post
I used to do compound radius boards and built a router contraption to do that. There is also analysis in the book (Appendix II.3) for "conical" boards, although any swept line will give you "flat" string lines which means the geometry can be pretty arbitrary.

However, once above ~16" fretboard radius, which is mostly what I build these days, the difference between a compound board and a cylindrical board is so small that it is easily buried in manufacturing tolerance, relief, drop-off, cold creep and seasonal movement. I've found that there's not much point to compound radius boards if the nut radius is greater than 16" and only do them (on request) if the nut radius is to be 10" or less.

There was a good article in American Lutherie maybe about 3 years ago called something like, "...cylinders almost do it..." which discussed the pros and cons of various surface geometries and came to much the same conclusions.
Yes... I calculated a while back that even a constant 10" radius would end up with about .01" or so rise around the 7-8 fret that would be likely planed and sanded away in the truing process.
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  #21  
Old 12-03-2017, 10:45 AM
John Arnold John Arnold is offline
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+1 on Frank's method. Works for me, too.

I have tried other methods, but I keep coming back to that one.
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  #22  
Old 12-03-2017, 10:47 AM
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murrmac123 murrmac123 is offline
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Quote:
Originally Posted by bausin View Post
>> I would appreciate any comment on the method I used to arrive at the two radiuses.

Murray,

To calculate the radius at the bridge, you will need to know the string spacings at the nut and bridge, the radius at the nut, and the scale length. The width of the fretboard is irrelevant.
To calculate the radius at the end of the neck, you will also need to know the distance from the nut to the end of the neck.

If you post those numbers, I can calculate the radii for you.

Steve
Well now, first of all, welcome to the AGF , Steve, and I am touched by your offer to do these calculations for me.

The fretboard referenced in the OP (along with a braced mahogany back and a jointed soundboard) has been lying covered in dust almost as long as this thread has ... I have had many many other things of more pressing importance to take care of in the interim, but my hope and intention is that next year will see these components come together.

As I say, I appreciate your offer to do these calculations, but I am not altogether convinced that they are in fact necessary ....I never think in terms of saddle radius (which I assume is what you meant when you said radius at the bridge) ... to me a saddle is a set of six discrete planes, each sanded (from above) to give an incrementally lower 12th fret action from E to e.

But again, welcome to the forum, and I hope to read more posts from you.
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  #23  
Old 12-03-2017, 02:24 PM
Alan Carruth Alan Carruth is offline
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What Frank says. I've been doing that for a long time, and it works. Sometimes it's too easy to get hung up on theory.
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  #24  
Old 12-03-2017, 09:01 PM
bausin bausin is offline
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>> You only need know the radius at nut and 12th fret, nothing else. Whatever the difference in radius between 12th fre and nut should be the difference between bridge and 12th fret.

Louie,

My interest in exploring a compound radius fretboard is to minimize the action of the strings above the frets. If the fretboard has a significant radius and the strings are farther apart at the bridge compared to the nut, then a fixed radius fingerboard will not be optimal. A conical section/compound radius will not have the errors of the fixed radius. To compute the correct compound radiusing, you need the factors I specified. If you predetermine the radii, without regard to the string spacing, the geometry will not be optimal.

>> A fretboard with constant center and edge thickness cannot be a conical section...

A fretboard surface, and therefore the fret tops, can be conical. If the thickness of the fb in either direction varies a bit, I don't care.
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  #25  
Old 12-03-2017, 09:26 PM
bausin bausin is offline
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Quote:
Originally Posted by murrmac123 View Post
Well now, first of all, welcome to the AGF , Steve, and I am touched by your offer to do these calculations for me.
Hi Murray,

Thank you for the welcome.

I have written a computer program to do the calculations since I got tired of doing them by hand over and over for different neck dimensions. No problem doing this for anyone that wants numbers.

Due to a math error in my original program, which over-estimated the errors with a fixed-radius fb, I became very interested in compound radiusing. When I fixed the mistake, I saw that in most cases the errors were too small to bother with. For example, with my ES-175 with a 12" radius and a TOM bridge, the max deviation of the action of the outer strings from what could be achieved with a compound fb is 1 mil. This can be improved to less than half a mil by changing the saddle radius to 12.6", which raises the outer strings at the saddles by 2 mils.
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  #26  
Old 12-03-2017, 10:46 PM
LouieAtienza LouieAtienza is offline
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Quote:
Originally Posted by bausin View Post
My interest in exploring a compound radius fretboard is to minimize the action of the strings above the frets. If the fretboard has a significant radius and the strings are farther apart at the bridge compared to the nut, then a fixed radius fingerboard will not be optimal. A conical section/compound radius will not have the errors of the fixed radius. To compute the correct compound radiusing, you need the factors I specified. If you predetermine the radii, without regard to the string spacing, the geometry will not be optimal.
Believe it or not, you only need the radius at the nut and 12th fret, since regardless of shape the fretboard should be a ruled surface, therefore everything from the string splay to the radii are proportional. If you want to split hairs you have to add double the action at the 12th fret to the radius at the saddle

Quote:
A fretboard surface, and therefore the fret tops, can be conical. If the thickness of the fb in either direction varies a bit, I don't care.
While you can shape the fret tops irregardless of the fretboard topography, you'll end up with variances in fret height, which would be noticeable with medium height frets, or hands with pudgy skin like mine. Maybe not noticeable with jumbo frets and a deft touch. It's also nice to seat frets well and have only very little material to remove off the frets.

If a "true" conical section is desired then one must know the distance from the nut to the theoretical divergent point of the lines of the two outer strings. Then for a given nut radius there can only be one end and bridge radius that satisfy the definition of conical section. This produces a fretboads that tapers in thickness. The problem with this is that the fret slots are cut normal to the bottom of the fretboard, not to the theoretical cone center, thus when you bend a string wuth a true conical fretboard, you actually bend "uphill," meaning the fret radius actually decreases slightly as you bend. Granted the difference is tiny, and lost likely when the frets are leveled and relief is set . Regardless the term is a misnomer.
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  #27  
Old 12-04-2017, 12:25 AM
bausin bausin is offline
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Quote:
Originally Posted by LouieAtienza View Post

If a "true" conical section is desired then one must know the distance from the nut to the theoretical divergent point of the lines of the two outer strings. Then for a given nut radius there can only be one end and bridge radius that satisfy the definition of conical section.
That's what I'm saying.
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  #28  
Old 12-04-2017, 05:41 AM
LouieAtienza LouieAtienza is offline
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Quote:
Originally Posted by bausin View Post
That's what I'm saying.
Yes... but what I'm saying is that this isn't necessarily optimal. In my opinion, it depends on playing style. If you play with your thumb around the "top" and you don't really bend strings, then I believe this is a comfortable arrangement that doesn't make the fretboard unnecessarily flat for the player high up. And I feel it makes it easier to pick, but the same can be said for a constant radius board.

If you do bend a lot, and you want low action, the you want the radius at the end of the fretboard to be larger than the theoretical, because this way you bend "downhill".
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  #29  
Old 12-04-2017, 08:01 AM
redir redir is offline
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I've always used a plane too, much faster then sanding and you can plane in the direction of string line. But I now follow that up with the sanding beam, I love the sanding beam. The beam is great for truing the tops of frets too. I have to say though, I've always wondered about the value of compound radius boards and if it's really just one of those things that looks good on paper VS the real world. I guess in the end every fraction of a fraction of an inch might count, maybe.

But anyway the beam is great none the less
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  #30  
Old 12-04-2017, 08:15 AM
Ned Milburn Ned Milburn is offline
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Quote:
Originally Posted by murrmac123 View Post
I am about to commence the shaping the fretboard for my first "proper" (I hope) guitar, and I am planning on doing a conical radius (or "compound radius" if you prefer) .

I rather like the idea that John Arnold mentioned on here some time ago ... he said that he shaped his boards starting with a defined radius at the nut, and maintains a constant center thickness and a constant edge thickness. I seem to recall that Charles Tauber said that was his preferred method as well.

Am I right in thinking that doing it this way, there is one, and only one end radius which satisfies these conditions for any given nut width, end width, and nut radius ? ie if you start off with a given radius at the nut, then the radius at the end is predetermined ?

I am 99.99 % sure that such is the case, but just wanted confirmation from those who have actually done it.
I do my radiused fingerboards the same. I don't think in terms of an actual radius measurement, but moreso a thickness measurement. I scribe a line about 0.8mm lower than FB edge on each side, scribble on the top, and then remove what I don't want. The scribbles let me make sure not to take anything from the top middle.

Now, to your specific question... The radius at the end of the FB will be different depending upon the fingerboard side to side width and taper. Makes sense, right...

Now you got it all, I think...
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