Hi, I don't play an instrument (yet?) but found this site and was intrigued. Trying to read up on the tech details to try a build. It seems that a lot of the CBGs seem to be in open G tuning. What scale length does that correspond to? Sorry if this has been answered already, but I haven't found it, maybe I just haven't found the right phrase to put in the search box.......
There may be some reason a particular tuning would require a particular scale length, but I don't know what the reason would be. Let me think about that question a bit. String tension is the only reason I can think of. Rather than explain it all here, you can read about string length and string tension at this link: Liutaio Mottola. If you exceed the string tension by a lot, then you break the string. Other than that, you can use the open G tuning with any scale length, assuming you pick the right strings.
When selecting a scale length, I consider ease of fingering and my preference is for a shorter scale length instrument. Most of the ones I make have a 50cm (a tad less than 20"), but then my instruments all tend to be diatonically fretted (seven frets per octave instead of 12 like the major scales) for easier learning/playing for novices. For chromatically fretted instruments, you will likely want a somewhat longer scale length so there will be sufficient room between frets for easy fingering, especially above the 12th fret.
When working with a new scale length, I often look to see what sized strings similar instruments use and either try them, or guitar strings of similar size. For instance if you decide on building a 3-Stringer, say a 24" scale, chromatically fretted, tuned to G-D-G', you can look at the standard set of guitar strings: E-A-D-G-B-e and see that the A-D-G strings would work if you tuned A back down to G. So, as a first attempt, you could try the 3rd, 4th and 5th stings from a set of standard guitar strings. If you are going to use magnetic pickups (pups), however, you should make sure all your strings are steel, and you may find you need to go with electric guitar strings. Piezoelectric pickups will work on all types of strings, even nylon.
Also, here is a link to an easy to use string gauge calculator recommended by Diane of Chicago.
You got it! I wish I could say things so concisely.
tone = scale + string gauge + tension
I think that the 2 main reasons open G is so popular is that it is a very "singable" key and most players use their CBGs to accompany singing....
If you want sort of a "middle of the set" (not using the heaviest string "E") selection of strings, you would be using A-D-G (5-4-3) out of a typical set... and a GDG tuning would be easy to get to.
A little experience will let you marry string gauge and tension and scale length to get a CBG that plays how you want it to feel...
Open G is popular because it is very easy to sing to and will "fit" the ADG strings...
Remember tone = scale length + string gauge + tension
You can adjust any of these to get to a sound you want... a little experience will let you find a combo that fits you.
the b est,