Well you can convert a 3 String CBG into a 4 string by either adding a 4th string to the existing neck (which may require making some extra mods to it) or by replacing the neck. I'm planning on converting my 4 String Cigar Box Guitar into a 6 String (maybe a 7 String) by making a new neck for it. However it'll be wearing Nylon strings to keep the tension down & tuned to Open G (but down a Half step so Open G flat). I also wanted a Russian 7 String Guitar but they're very overpriced.
it all depends on how the 4 strings are tuned. you could tune it GDgd then just use the GDg and ignore/mute the d string. If you wanted to use all the strings then just play the same fret on the d as you are on the D string it will just add an octave note. Shane sometimes uses other tunings than GDg .
You'll really need a Special Conversion kit. The next idea I had was to convert my 4 String Cigar Box Guitar into a 6 (or maybe a 7) String cause I don't want to built a new instrument & get another Cigar Box, I wanted to simply swap the neck
Your 3 string guitar is usually tuned ( 1 - 5 - 1 )
The 1 is the root note of your chord and the 5 is the 5th note of the chord and the other 1 is the root note at a higher octave.
The 4 string is usually tuned ( 1 - 5 - 1 - 3 ).
Your choices are:
A: Keep the 3rd note string of your 4 string guitar tuned as is and add that note to the chord you are playing.
B: Mute the 3rd note string.
C: Tune the 3rd note string to a 5th note at a higher octive than the other 5th for a fuller 3 string tone.
I think C you'll get a much fuller sound. Well we could have a 7 String version tuned DGBDGBD like a Russian 7 String Guitar cause whatever yo do on the bottom 4 strings can be done on the top 4 as well. Converting a 4 string Cigar Box Guitar to support more strings might require making a new neck.
I made a Baritone conversion neck and put it on a Strat. It has Dulcimer fretting, I call it the Ducitar. 6 strings at 28" scale.
It's tuned open C : C/G/C/B/C/C. You can play Bass chords on the 3 top - lower tuned strings, Baritone Guitar on the 4 bottom - high tuned strings or just fret the 2 - C strings while strumming the others for Dulcimer.
Takes awhile to get used to it, but it's fun.
Actually it's G not a B. Well Converting a 3 String CBG into a 4 String could be for if you want to advance to more Strings but you don't want to make a new instrument. It might save alot of money because you're simply rebuilding an instrument. I've modified my 4 String CBG (that I made w/ my Father) into a 6 String by making an attachment to widen the neck. It's a Sawtooth Profile so I had to sand it smooth. Because the neck was shorter & I ran out of really heavy gauge strings, I only had 7s available w/ me so I had to tune mine up a Minor Third from E Standard to High G Standard so yeah a Terz Guitar Conversion.
I was able to get away w/ John Pearse #450 Strings for my 4 String Conversion Cigar Box Guitar (it used to be a 3 String), but because the scale length is 2 inches longer than a Standard Tenor Guitar (which would be 23 inches) the GDAE Tuning (I use it to play Violin pieces down an Octave, I'm working on Vivaldi's 4 Seasons on Tenor Guitar in GDAE Tuning) sounded much more solid on the Low & High Ends.
J.N. Guitars made the Cask Guitars which are Cigar Box Tenor Guitars. They're also working on the 6 String Version called Cask VI:https://www.youtube.com/watch?v=_3-uW_OAURg
You were right Oscar about that stated B being a G instead, my mix up.
All my 3 or 4 string CBG's have been 25" scale except for the last 2 I built were 24" scale.
Love those guitars you posted, they look great.
The JN Cask Cigar Box Tenor Guitars are perfect for Orchestral String players that wanna strum
We would need to make a conversion kit because let's say you want a 4 string Cigar Box Guitar but you don't want to build a new instrument. Modifying an instrument could save you money.