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hi

Two questions here:

My first question regards the "optimality" of compound radiusing the fretboard.

Now, I realize that compound radius is the phisically right way of doing it, but is the difference from the traditional way really that noticable to be worth the extra trouble (assuming that I want to be able to achieve the lowest possible action)? - Im talking about flat-ish radius here - 12" and above

the second question is what's the best way of doing a compound radius board?

will having a compound radius block machined and working it with sandpaper on the board (with small movement) be a good method, or should I go through the trouble of building something like this:

and using is a-symmetrically to get the different radius at each end (I have a belt sander and a metal shop free access to build it).

Or should I just forget all about it and get one of stewmac's aluminum radius blocks?

I will welcome any thaughts/suggestions/advice with great thanks

Cheers, Binya

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Compound radius is the way to go. If the fingerboard was the same width at both top and bottom, then it could be thought of as a cross section of a cylinder, but it's not. A fingerboard is a cross section of a cone which has different radius' at all points. Very small 'single radius' fingerboards are prone to fretting out, which means the string loses clearance when you bend it. Compound radius solves this problem, so the strings can be set lower without fretting out. It's quite difficult to build a jig to make a compound radius by machine, but luckily it's easy with a jack plane. If you align the edges of the plane with the center of the FB, you'll get a cylinder. If you align the edges of the plane with the sides of the FB, viola....er voila! A compound radius is achieved. This sounds hard, but in practice it's easy. Just use a fairly long body plane. Mine is 22", but I'm sure you could get exellent results with just a 12".

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Compound radius is the way to go. If the fingerboard was the same width at both top and bottom, then it could be thought of as a cross section of a cylinder, but it's not. A fingerboard is a cross section of a cone which has different radius' at all points. Very small 'single radius' fingerboards are prone to fretting out, which means the string loses clearance when you bend it. Compound radius solves this problem, so the strings can be set lower without fretting out. It's quite difficult to build a jig to make a compound radius by machine, but luckily it's easy with a jack plane. If you align the edges of the plane with the center of the FB, you'll get a cylinder. If you align the edges of the plane with the sides of the FB, viola....er voila! A compound radius is achieved. This sounds hard, but in practice it's easy. Just use a fairly long body plane. Mine is 22", but I'm sure you could get exellent results with just a 12".

about the hand plane method: I own a 18" plane (and some skill as well) and understand the logic behind your way of doing it, but I don't see myself achieving a consistent and "correct" radius across the width of the board quite so easily. got any tips for that?

Edited by avdekan
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Without wanting to come across like I’m re-opening that huge tanker of worms:

A fretboard is a compromise between practicality and the PerfectSystem (which doesn’t and will never exist as I will explain). There are many physical shortcomings which employed methods such as compound radii, compensated frets, nuts, etc. can only improve upon, and in a lot of cases detract from the practical maintainability of the instrument. Ever considered replacing or simply just recrowning compensated frets? This is stuff epic nightmares and wasted time are made of.

Anyhoo, compound radii. A compound radius is – as mentioned – a cross-section from the surface of a cone which possesses two radii at either end and a taper. Primarily this helps with the overall action of the string around (as opposed to “across” by implication) the fretboard as the bottom surface of straight strings are (ideally) held above the crown of the fretwire at marginally larger radii than the fretwire crown’s surface radii. This is barely perceptible in practice, and probably not even achievable given the flexible nature of the materials we work with and the balance of forces counteracted in them during use. When a string is bent however, the compound radii no longer works perfectly (in theory). It works better than a cylindrical radius of course, although there are still problems due to the string path being perturbed from a straight line to a skewed line. If you extended string paths beyond the nut as a straight line, the bottom surfaces of each string would eventually intersect at a point as they themselves form lines around a cylinder with a (theoretically) perfect distance above the fret crown surfaces. Bending a string from it’s resting state along the side of that conic section still possesses the potential to “fret out” same as a cylindrical section, only is far less likely to do so. I haven’t even gone to the lengths of factoring in string gauges to my pedantatheory :-\

Compound radiuses are still a degree of compromise, although a magnitude better than single radii. This of course – same as most of my posts – doesn’t answer the question, but hopefully it illuminates and encourages discussion and ideas on the inherent flaws and the compromises we balance or accept in our step-above-tea-chest-bass instruments :-D

I think single radius instruments are fine, as they are easy to maintain and don’t require excessive time and skill to achieve excellent playability. Compound radius instruments are more difficult to create, and require a level of understanding from the owner or person maintaining the instrument to keep it working well.

In reality, most people will hike up the action and fiddle with their rods (har har har) than consider slightly more dynamic three-dimensional geometry!

Sorry to go off-topic. I wrote this at work and am theoretically getting paid to do so which makes it excusable.

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I look at it like this - A 10"-16" compound radius board may have a noticable advantage over a straight 10" radius board, but not so much over a straight 16" board. Speaking in terms of low action and fretting out.

I like a 16" radius, and I don't find a compound radius board really any more confortable to play, so I'll not fool with one.

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I look at it like this - A 10"-16" compound radius board may have a noticable advantage over a straight 10" radius board, but not so much over a straight 16" board. Speaking in terms of low action and fretting out.

I like a 16" radius, and I don't find a compound radius board really any more confortable to play, so I'll not fool with one.

16" radius is tough to play barre chords on though. Personally, I can get very low action with 12" radius and a slight fallout past the 17th fret

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+1 on the straight 16" Radius

<opinion>

I have played most of radius available and none play as well as my 93 RG470. It has an 1 11/16" - 2 3/4" with a 16" radius and a super slim Wizard Neck. A neck is a total package and as long as it is comfortable I say use what you like. Hell that is why we build guitars....

</opinion>

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16" radius is tough to play barre chords on though. Personally, I can get very low action with 12" radius and a slight fallout past the 17th fret

I've never felt that way, but everyone is different.

I've had some pretty low action on 12" boards too, but I don't think they feel as good. I guess it all depends on your hands.

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This is also a reason why I re-radiused the saddles in a TOM to suit a 16" radius rather than the usual 12" for my 27" scale Explorer retrofit neck (obviously the fingerboard and frets have been radiused to 16" also). I prefer 16"-20" (hohoho) as smaller radii play slowly with my style.

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avdekan, making an extremely even compound radius with the plane is quite a bit easier than you would think, especially if you're skilled with your plane, which you are. I was skeptical at first too, but I was bolstered by William Cumpiano's exellent book and gave it a shot with an inexpensive chunk of Ipe. It came out so good I did the second one with some brazilian rosewood (!) I have stashed. No problems planing either one. Like many things you do with a plane, your fingers will tell you more than your eyes can see. I calculated the two radii (?) a simple, but probably stupid way. I made a pile of miniature cardboard FB's with the same relative dimensions and taped them together edgewise until they made the cone cross section. Then I just measured the size of the top and bottom circles. If I were smart, I would have done this in a CAD program real easy. With a template for the top and bottom, planing the FB to match the curves was a piece of cake.

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