Glad I searched the archives before I was about to post.
I just finished building a mahogany baritone uke sized cuban tres for myself:
View attachment 137554
I have an inexpensive cuban tres steel string from Paracho, Mexico, via Musician's Friend, but what kept me from really enjoying it was the wide neck, steel strings, and small guitar-size deep body which is still a lot bigger than I like. I find ukes much more comfortable to play and having been born in cuba but not back there in 60+ years, have become enamored with the sound of the tres cubano as played by masters - look up tres cubano 4 genios convergencia for a very sweet example. I am just getting started and enjoy this one much better than the real version.
For those unfamiliar, with the three string pairs, the chords and scales are like an uke with the A string missing, easy to translate and learn, at least at my casual level. There is an excellent little guide booklet, Cuban Tres Guitar Chord and Scale Book, by Rudy Furlan, that explains the tuning, scales, and chords with workarounds for the chords that need more than three notes - online for download at
https://docplayer.net/18378726-Cuban-tres-guitar-chord-scale-book.html
A few points to consider for converting an inexpensive baritone uke - assuming you will be using nylon or flourocarbon uke strings, not looking to put steel string tension on a nylon string instrument (above comments apply):
-If you are not into replacing the bridge, you could try putting notches into a new saddle to reposition the strings - this worked for me in converting a small steel string. You'll likely need to start with a new saddle as these notches will be quite deep to hold the strings in place at such an angle from their original paths, but if the action is already too high it may be a quick fix with existing saddle. You will have to make a new nut of course.
-Drilling - Don't do this on anything other than a cheap uke that does not have high monetary or sentimental value. If notching a saddle doesn't work, you could most likely drill 1/16" or smaller holes through the bridge and top and use small glass or metal beads on the underside to keep string knots from pulling through. You likely have a fan brace right in the middle where two strings need to go, and may well have fan braces where you'd want some of the other strings. I suggest looking carefully with an inspection mirror to get an idea where your braces are, put a tape marker on your drill bit and clear the dust regularly - if you see white wood dust or are going deeper than you expect, pull out and start over at an angle to miss the braces.
- On mine I have an 18.5" scale length, meeting the body at the 12th fret, which has the bridge in pretty much the same place on the body as on a good baritone that I have. The approximate flourocarbon string sizes that work on mine are:
1. Low E - .041 inch 1.05 mm
2. High E - .024 inch .62 mm
3. Mid C - .029 or .30 inch .74 mm
4. " " " " "
5. High G .022 inch .57 mm
6. Low G .036 inch .91 mm
I've found an unwound flourocarbon .041 inch / 1.05 mm in the Living Water Baritone Low D set that works for me on the low E. if your scale is longer then normal baritone strings should work fine. If you don't mind wound strings you'll have more choices. You'll have more total tension with six instead of five strings, so don't go too thick and avoid high tension string sets.
Hope this helps,
M Vinsel
Monroe, Washington USA