Compund Radius Disparity

[MrMuckle]

What's the greatest difference in radii one can have on a guitar? 7.25" is very comfy at the neck, but is 16" at the bridge overkill? I guess what I should be asking is, given a certain radius at the neck, what is the minimum you need at the bridge so you don't "fret out" when bending?

[Woodenspoke]

I would no go past 12 with a 7.5. But I have never tried it with a 16 which is really flat. The other issue is the bridge. Most bridges are 12.. Figure out the bridge radius first,

[Buter]

And...

If your nut end is 7.25" and your bridge is 12", that is not the radius you put in your fretboard.

If you already know this just tell me to Foxtrot Oscar - what you are aiming to achieve is a constant cone shape with the strings and have the fretboard a constant distance from the strings (not taking into account relief, higher action required near the middle of the strings and fretboard fallaway...). I'm not gonna do the math but if you have a 7.25" nut and a 12" bridge radius, the radius at the end of the fretboard will be something like 10-10.5". If you put a 7.25-12" radius into the fretboard, your bridge will not be flat enough to benefit, in full, from the compound radii and the outer strings will be the ones that the action is based upon, making the middle strings require a higher action than needed (but still lower than a cylindrical shaped fb).

There's a formula in Dan Erleweine's setup book that will tell you how to figure out the radius of a cone at any given point on the cone. The book is well worth the money.

I spent a lot of time making various jigs and trying different ways of doing coumpound radius' and I've gone back to a single radius. What I've found is that, for me, it was a lot of extra work without any perceived benefit. Perhaps others with super sensitive fingers could tell you the exact radius of any given fb, but it didn't really make too much a difference to me. In fact, I had one where I could get the action really low, and ended up raising the action more than needed just because I liked the feel better. Go figure.

Good luck

Buter

[Woodenspoke]

Maybe you mean the strings radius at that point using a 12 bridge. Try finding a fixed bridge that will be perfect.

Guitar building is not an exact science as evident by whats been done. But a compound radius is a refinement none the less. I have never seen a fallaway on a compound board or heard anyone consider adding it? Not that fallawys come up in discussion here all that often.

I dont know of any way to create a compound radius with a constant string height. But I have never noticed a huge difference except the ability to lower the action.

[Buter]

Hi George

Not sure if you are misunderstanding me or just being a pompus ass.

I was simply trying to point out that if you are going through the hassle of doing a compound radiused fb, you are probably doing it to get the lowest possible action so you might as well find out what bridge radius will work best with your camber or which camber will work best with your selected bridge.

If you are running a 9-12" camber, a 12" radius bridge is not ideal, a 14 or 16" radius would be preferable to gain maximum advantage of the cone shaped fb.

It is easy enough to work out the radius anywhere on a cone and from that, knowing your desired nut radius and your bridge radius, you can find the perfect radius for the last fret on your board. On the other hand, if you are using a pre cambered board with a compound radius, you can find which bridge radius is the closest to ideal.

The constant string height thing was one of those things that made sense in my head but looks like utter shite to anyone not stuck inside my head with me. By constant I was thinking of the lowest action possible for every fret (which, of course, is nothing like a constant distance). Fall away is something that has only just been pointed out to me and was just one of the factors that would make my 'constant' string height unrealistic.

Compound radius fb's are indeed a refinement and are ideal for anyone looking for the lowest possible action. The ability to make a cone shaped fb is also a great trick to have up your sleeve. Super low actions don't suit all styles or all players and I've found that a 12" radius works great for me and I don't really want the action any lower than it is on a 12-incher.

TTFN

Buter

[Woodenspoke]

OK Foxtrot Oscar