I highly recommend using the latest and greatest version, instead of this one. This one will not be updated anymore.
Version 4 is available here: https://www.thingiverse.com/thing:5745382

I plan on making a upgraded version of my project where there will be a rod that stabilizes the neck and adjust string action (height).

Hello there. I designed a 3 string ukulele-like, guitar-like, balalaika-like instrument that can be tuned however you like or played however you like. I used nylon guitar strings, but you could experiment with metal tuning pegs. I've experimented with open C CEG tuning, balalaika EEA tuning, and ukulele minus one tuning CEA and it all sounds great.

https://youtu.be/LNCmR7EJ6GE

Video comparing the instrument printed in PLA and PETG

https://www.youtube.com/watch?v=Eq6zMpVo5cQ

Parts list: Chrome Tuning Pegs Machine Heads https://www.amazon.com/dp/B00EQ2ABD4

You can use other ukulele tuning pegs if you want.

I bought fender nylon strings, but you can use ukulele strings or experiment with another type of string. https://www.amazon.com/dp/B003B07GXA

Also, you will need an adhesive to hold the neck together. The neck and body slot together, but for the adhesive I used Krazy glue.

The strings need tied on at the bottom like on a ukulele. The head-stock has 5 holes so you can play this instrument left or right handed.

I made a demonstration video of the project: https://youtu.be/LNCmR7EJ6GE

Update: I created 5 more bodies that you can use. The model you see in the video is model B, which stands for Balalaika. I've also made a circle body (model C), an oval shape body (model O), a guitar-like body (model G), a V shape body (model V), and a body that looks like strat (model S). I tried the model G body and it looks nice, but I used a little too much glue.

Update: I've added some more wacky bodies, including a crescent moon body, heart body, and a star shape. I cannot print some of these bodies because my Prusa Mini+ is not large enough. I will include a .step file soon.

I've added an option to convert model B (balalaika body) into a V shape body (model V) if your printer is too small. I've included the file model_v_upgrade. Print two of the same file and glue them onto the bottom of the model B body. This part doesn't need a lot of infill. I also added a ukulele style body (model U).

I have also included a .step file of Model B. You can customize this however you want. If you move the nut or bridge, then you'll have to adjust the fret spacing.

I've made a functioning fretless neck with finger guide, great for eastern music. I have also made a diatonic neck for those who want to use their instrument like a strum stick.