Compound Fretboard Raduis

[Hman32123]

Does any one here know how to make a compound fretboard radius like some of the necks they have at warmoth (10 at the nut, 16 at the end of the fretboard)

[GregP]

A compound radius is just a cross-section of a cone. You can make them by hand with a flat beam instead of a radius beam-- instead of running it parallel to the 'virtual' centre-line, you run it at "fanned" angles radiating from the imaginary 'tip' of the cone. I don't know how difficult this is, but I've seen the technique described elsewhere... the Koch book maybe?

This very forum also has a few links to jigs for doing the job. One jig moves the router over the fingerboard in the set radius, and another jig moves the fretboard against a belt sander at the set radius... yet another one uses the "belt sander" approach, but in conjunction with the router. Lots of ways to skin the cat.

The edge of the fretboard should be the same level, though. The middles of the nut-end frets (the tighter radius) should be raised higher. If you have the same height of middle but with lower edges, you will fret out.

A quick Google should give you lots of info... this one doesn't tell you how to "do" it, but it has some useful illustrations. Noting especially that what we call "compound radius" is more accurately described as "conical radius"

http://ratcliffe.co.za/articles/radius.shtml

Pinned within this very forum (the "search" tool is your friend, too):

http://projectguitar.ibforums.com/index.ph...compound+radius

[Hman32123]

thanks

[Untitled_Project]

After 3 years of being gone and forgotten.......

IT'S ALIIIIIIVVVEEEE!

Got a quick question about bridges and compund/conical fretboards. My nut will be a 10" radius and the bridge is at a 20" radius. The neck will be 24 frets at 25.5 inches scale length.

What will the fretboard have to be radiused at? (10"-0 fret to ? at 24th fret)

Edited November 6, 2010 by Untitled_Project

[Ken Bennett]

After 3 years of being gone and forgotten.......

IT'S ALIIIIIIVVVEEEE!

Got a quick question about bridges and compund/conical fretboards. My nut will be a 10" radius and the bridge is at a 20" radius. The neck will be 24 frets at 25.5 inches scale length.

What will the fretboard have to be radiused at? (10"-0 fret to ? at 24th fret)

Off the top of my head...

The scale length is irrelevant because the ratio of the length from the nut to the 24th fret to the overall scale length is the same for any scale length.

It seems that the radius at the 12th fret would be the mean (average) of the two radii at the ends: (10 + 20) / 2 = 15

Furthermore, the radius at the 24th fret would be the average of the radius at the 12th fret and the radius at the bridge: (15 + 20) / 2 = 17.5

This may be wrong as I am notoriously bad at doing arithmetic in my head. Also this does not take into account the fact that the string spread is greater at the bridge than it is at the nut. That may or may not matter. My guess is that it does matter, at least a little, but maybe not enough to worry about.

I'm guessing 17.5" radius at the 24th fret.

Edited November 8, 2010 by Ken Bennett

[Prostheta]

Just to clarify; a "conical" radius is a surface section of a cone. A compound radius is two or more radii with specific transition points.

Warmoth really screwed up our lexicon.

An example of a true compound radius would be a board with a 10" radius from frets 1-12 and 16" 13+. It just means the centre of the fretboard is lower. It can also describe a non-linear transition between radii which does not satisfy the conditions of a conical radius.

[Untitled_Project]

I'll be looking to do a conical radius. I imagine that is what the people at floyd rose were thinking when designing their nut at a 10" radius. And my floyd has a radius of 20".

I want the action to be tight and even.

Can anybody verify Bennett's calculations? It seems right to me.

[Prostheta]

If I'm thinking correctly, then a cone can be reduced to a right-angled triangle with the perpendicular distance from the adjacent to the hypotenuse being the radius at any given point. So yeah - scale length is indeed irrelevant as the radius of any given point can be calculated from the gradient, which in turn is calculated from the radius of two specific points. In the case of a fingerboard, the nut radius and that at the bridge (usually).

I think that is right anyway. Bleh.

Untitled_Project: Yep, a tight even action won't be given by a truly compound radius as the central strings will suddenly have a higher action where the upper radius kicks in. It's feasible to run say, something like 10" from frets 1-7, 12" 8-12, 16" 13+ so the transitions aren't too crazy. It'll be more of a perceived change between radii unlike a conical profile though.

Edited November 8, 2010 by Prostheta

[Untitled_Project]

Okay....

Your explanation took me for a ride then when we stopped by the side of the road to tinkle, it drove off without me.....leaving me lost.....

So how do I go about making a conical radius of those 2 points?

[Ken Bennett]

If I'm thinking correctly, then a cone can be reduced to a right-angled triangle with the perpendicular distance from the adjacent to the hypotenuse being the radius at any given point. So yeah - scale length is indeed irrelevant as the radius of any given point can be calculated from the gradient, which in turn is calculated from the radius of two specific points. In the case of a fingerboard, the nut radius and that at the bridge (usually).

I think that is right anyway. Bleh.

Untitled_Project: Yep, a tight even action won't be given by a truly compound radius as the central strings will suddenly have a higher action where the upper radius kicks in. It's feasible to run say, something like 10" from frets 1-7, 12" 8-12, 16" 13+ so the transitions aren't too crazy. It'll be more of a perceived change between radii unlike a conical profile though.

If you used GregP's method (making the compound radius with a flat bar), then there won't be any transitions. The radius changes continuously as it does with a true cone.

[Prostheta]

Both methods have their uses though. Compound is very simple to create.

[Ken Bennett]

Both methods have their uses though. Compound is very simple to create.

Right. The compound radius is simple to create. There seems to be some confusion about it though. For example, you said:

... a tight even action won't be given by a truly compound radius as the central strings will suddenly have a higher action where the upper radius kicks in.

That doesn't seem right. If the FB is a true compound radius (conical), and what you describe happens (middle strings have higher action at the upper end of the FB), then the radius of the bridge saddles is wrong. That's the topic that got me into the thread: the question about coordinating the FB radius with the bridge radius. When that's done correctly, the action will be consistent.

Take a Les Paul, for example, which has a 12" radius at the nut, the whole fretboard, and at the bridge. Then if you change the FB radius from a straight 12" cylinder to a cone--by flattening the board at the higher frets--, then yes, the action will be higher for the center strings in the upper register. You have to finish the job by also changing the radius at the bridge flattening it even more than you did the FB.

So if a fretboard has a compound radius of 10" at the nut to 17.5" at the 24th fret, and the bridge has a radius of 20", then the action will be totally consistent across the board.

[Prostheta]

Sorry Ken - you're labouring under the misapprehension that a compound radius is a conical surface section. It's not - a compound radius uses multiple constant radii over specific sections of the scale with defined (or at least, non-linear) changes. For example, a simple 12" radius from the nut to the 12th fret and then from there a single radius of 16". A conical radius is generally the surface section from a cone; a linear transition in radius from the nut end to the saddle end. In a truly "compound" radius, the transition points are where the action changes a little oddly. In this example, the difference between the 12th and 13th frets.

You're right about adding a larger radius in relief at the end of the fretboard. Works the same as simply sanding in falloff, but you would also have to alter the bridge radius on a LP ;-)

There is a lot of confusion over this as "compound" has incorrectly been bandied around for years as a term referring to conical radii. It comes down to words more than anything, since what most people think is a "compound" radius is in fact a conical radius - not a "true" compound radius.

Realitically, compound radii are poo and thankfully not in common usage (to my knowledge) since conical and "non-linear transition faux compound radii" (your LP example) aren't that difficult to dial in for instant gratification. I'm by no means a compound radii fan - I think single, modified single (catchier than "non-linear transition faux compound radii") and conical are just fine. It's silly how many terms in common usage are actually incorrect. Such as tremolo and vibrato. I'm sure that common usage has all but consigned the original meaning of "compound radii" to history, so we can all live happily in ignorant bliss. Just got to kill all other non-guitarists to finish off the trem/vib thing.

History is defined by the winners, and after all - conical is a winner.

</pernickerty>

Edited November 9, 2010 by Prostheta

[DC Ross]

I'd love to see an example of Prostheta's explanation. Better yet, I'd love to play one and see how much it would fret out on the outer strings.

"Compound radius" is defined pretty much everywhere as a section of a cone, as Ken describes:

http://www.stewmac.com/freeinfo/a-compoundradius.html

http://www.sweetwater.com/expert-center/gl...-CompoundRadius

http://en.wikipedia.org/wiki/Fingerboard#Radius

[Prostheta]

Gah, I spent an entire hour trawling through links and some of my books trying to find reference to this and drew blanks. Curses. I think that (surprisingly) the Wikipedia article was closest when referring to "example 4" which looks like the profile of a board having had a transition to a larger radius dialled in higher up. Your outer strings thing bothered me when I first thought about it too, but my biggest thought was to the "non-linear" change in action.

Conical for president.

[westhemann]

"Tube" is more accurate than "valve"

[Prostheta]

I won't even ask why you think that. I'll leave you to wallow in your ignorance as an example to others on what not to do. :

[westhemann]

"Hood" is more accurate than "bonnet" for the thing that covers the vehicle's engine..and "bloody" is not even a proper expletive...

A hamburger is a better meal than fish and chips ,and Mr. Bean is not funny.

And it is spelled "color" and "Aluminum"

[westhemann]

History is defined by the winners, and after all - conical is a winner.

Oh..and by the way,since your definition of "compound radius" being different from "conical" does not appear anywhere that i can find on a short (10 minute) internet search,seems like "compound" is in fact the winner.

Wikipedia defines a compound radius as "radiused at the nut,with a linear bridge"....

By 2he way,I prefer a simple 10 or 12" radius...around here we call that a "Texas beer can" radius

[Prostheta]

What the hell is a linear radius at the nut? What the hell is a "linear radius?". Infinite?

[Ken Bennett]

Gah, I spent an entire hour trawling through links and some of my books trying to find reference to this and drew blanks. Curses. I think that (surprisingly) the Wikipedia article was closest when referring to "example 4" which looks like the profile of a board having had a transition to a larger radius dialled in higher up. Your outer strings thing bothered me when I first thought about it too, but my biggest thought was to the "non-linear" change in action.

Conical for president.

Well, we agree on the main point: the bridge must be altered if the fretboard is altered.

It may not be absolutely necessary, but a compound radius feels pretty good. It's definitely an improvement over a 7.5" constant radius.

I have tried different things and settled on a 12" radius for all my guitars and basses.

That may change if I build a bass with 6 or more strings or if a customer wants a tighter radius at the nut.

Edited November 13, 2010 by Ken Bennett

[westhemann]

What the hell is a linear radius at the nut? What the hell is a "linear radius?". Infinite?

Linear bridge..not linear radius...Linear....in a line...no radius.....flat.....

Calm down boo....

Means a radius at the nut,flattening out to no radius at the bridge.

[Prostheta]

Bleh. Wording is bandied around so easily, and often without thought. Fair enough. The plebians can be left to wallow in their inaccurate descriptions of subtly (well, hugely) different concepts using ineptly broadened terms. I'll just stand here in my sturdy rubber boots whilst you splash around in your own filth then. :

As you can tell, my beer testing is progressing well. Conclusions to follow.

[westhemann]

I'll just stand here in my sturdy rubber boots

Won't you look silly?

plebians

You are a plebian as well..if you don't know this,maybe your the one with the ineptly broadened terms?

Beer is awesome,but not as awesome as Tequila...

Thus spake the tequila drinking Plebe

[Ken Bennett]

What the hell is a linear radius at the nut? What the hell is a "linear radius?". Infinite?

Linear bridge..not linear radius...Linear....in a line...no radius.....flat.....

Calm down boo....

Means a radius at the nut,flattening out to no radius at the bridge.

Even after reading the wikipedia article, I couldn't imagine this ever happening in real life, a radiused nut and a flat bridge. But I understand it in theory, and I see how it is a type of compound radius that is not conical.

Then I got a call from Nechville Banjos. They are sending me a neck to do a fretboard inlay, and wanted to remind me to be careful not to change the compound radius when I level the inlays. Radiused fretboards on banjos is a new thing. Nechville may be the first. I have talked with them about it before. They said that their radius is not exactly like a normal compound radius. I wonder if that means that they are leaving the bridge flat?

Also, some classical guitar makers use radiused fretboards now. Do they have flat bridges too?

These banjos and classical guitars may be two examples of the non-linear compound fretboard radius as described in wiki piece.

I'll measure the Nechville. It should be easy to figure whether it is a cone section or not. And I can find out whether they are using a flat bridge.

Edited November 14, 2010 by Ken Bennett