Banjolin (Banjo Mandolin)

As an luthier & printer, I believe the banjo is a perfect instrument for printing since the component that has the biggest effect on tone (the drumhead) is a standard component purchasable at any music store. Printing can even improve on the banjo in two major ways; weight & water resistance, for a great cheap travel instrument that still sounds great. I opted for metal frets because metal strings would eat through plastic frets in a single practice session.

Banjolins are small banjos tuned like mandolins, and so they are played primarily with a pick. To learn to play it, look for a tutorial on mandolin playing rather than banjo playing. 

You can make and play the Banjolin without the Resonator and Rest and it will be quieter and more muffled. The resonator redirects the internal sound pressure waves back out the front projecting the sound outward much like the hole on an acoustic guitar.

Printing Notes

The 3MF files show the correct orientation to print these models No Support Needed

I have prepared the 3MF files to optimize strength on the parts that need it. I print this model with a 0.8mm Nozzle for most parts and a 0.4mm nozzle for other parts that need the accuracy. You can use any nozzle you want but keep an eye on which parts I prepped with 100% perimeters and that the neck especially needs a very high infill.

I have printed mine with PLA which has been perfectly suitable, The original prototype has held up for 2 years, though there were some cracks in the Ring after 2 years of wear and sun damage so if you have a stronger material, the Ring is the most important piece to use it on.

Non-Printed Components

• Threaded Inserts
  • Ruthex M2 (8)
  • Ruthex M4 (13)
  • Ruthex M6 (1)
• Hex Bolts
  • M2 x 10mm (8)
  • M4 x 20mm (12) 
  • M4 x 40mm (1)
  • M6 x 20mm (1)
• String Hardware
  • Stewmac Banjo Fretwire
  • Strings (.037 .024 .014 .10)
    • Get an electric guitar string set that has 4 strings close to these values
  • Gotoh Planetary Ukulele Tuning Keys
• Drum Hardware
  • Remo 6 inch Tom Head (Any brand should be fine)
  • Lug Screws (Just Music Justin Spannschrauben JTR42)
  • Lug Nuts (Gibraltar SC-LN 7/32")

Tools Required

• Drum Key
  • For tuning the head
• Metal Files 
  • For shaping the frets - A set of fret files is ideal but one large flat file and one small metal file is sufficient.

Assembly Instructions

Prep Work

• Insert all the threaded inserts

• Glue in side dots
  • Using a contrasting color filament to the neck, glue the end of a strand of filament into the holes on the side of the neck and cut it flush to the profile of the neck

Fret Work

If you don't have the tools for this step, you can take the neck piece to a local luthier and they can do it for you. 

1. Press or hammer fret wire into each slot
   • I carefully heated mine with the side of a soldering iron which made it easy but very risky
2. Level and dress the frets
   • If you don't know how to do this, watch this tutorial
   • Note: This small instrument does not have a Truss Rod, If you do have a problem with the neck bending, try printing the neck with a sturdier filament or higher infill

First Assembly

• Attach Tailpiece to Rim (Put Strap Pin outside bolt)
• Attach Neck to Rim (Put Strap Pin on outside bolt)
• Attach Headstock to Neck

Drum Assembly

1. Press square lug nuts into the bottom of the rim
2. Put Drum Lugs through the ring and attach the ring and drum head to the rim
3. Tune the drum to a fairly high note but not so high that it breaks the ring
   • If you haven't seated a drumhead before, watch this)

Final Assembly

1. Attach the Resonator to the back of the Rim
2. Attach the Rest to the resonator
3. String up and tune the banjolin
   • Here is a good tutorial, though on My model there are only 4 strings with ball ends not loops and they are held in place by bolts on the tailpiece not by hooks
   • The nut will slide around a bunch as you get it in tune but as the tension rises, it will stick in place. You can use a little glue if you want.
4. Move the bridge until the 12th fret makes a note exactly 1 octave higher than the open string on each string
   • You will likely need to angle the bridge to achieve a good intonation on each string
5. File the string slots on the nut and bridge to achieve the desired string height
   • This is somewhat optional, but will greatly increase playability

Bridge Notes

Every instrument will come out a little different which makes the bridge and nut setup the last step to compensate for everything, maybe it's the brand of drum head you chose or how tight your printing tolerances are or what filament you used.

I've included the bridge model that worked for me but if it is too tall or short for you, you can create your own version with this OpenSCAD file I made awhile ago for this very purpose.

Finally

I know that this looks like a lot of work but it's not as hard as it looks and it's worth it. 

There is no case where a 3d printer today can print out a fully formed instrument that is more than a toy. After 2 years of testing and iteration I believe this Banjo is worth the time it takes to build (which is still way shorter than a traditional mandolin kit) and if you cant do the labor yourselves there are local instrument builders who can professionally do the task of fret installation for less $$ than you might think. All in all you should be able to build this project in a weekend even if you have never looked into instrument building.

Happy picking!