Soprano Ukulele (fully functional and easy to print)

Body length is 240mm, so make sure your print area is large enough.

The instrument is assembled from several printed parts that are glued together: body, back lid, neck, headstock, fretboard and bridge. Saddle simply slots into the bridge, there is no need to glue it.

You will also need ukulele tuning machines and ukulele strings.

The neck is designed for embedding a “truss rod” for increased stiffness. You can get away without using it, depending on your print settings, but I don't recommend that.

Printing

I used PLA for all parts, but feel free to experiment with other materials.

Use at least 3 perimeters and 15-20% infill. Print large parts with 0.2mm layer height (those can benefit from a 0.6mm nozzle as well), fretboard and bridge with 0.1mm layer height.

You will have to use supports for the cutout in the neck, but it should be very easy to remove them and the supported surface won't be visible.

Manual multi-color printing

I use a simple technique to print with multiple colors in one layer:

• In PrusaSlicer, increase the number of extruders
• Assign different colors to both extruders (optional, just for visuals)
• Set Tool Change G-Code to:

{if layer_num >= 0}
;TOOL_CHANGE {previous_extruder} -> {next_extruder}
M600 Z100
{endif}

• Add the object you want to print (multi-part STEP should work automatically; if you select multiple STLs, they should be loaded as parts, if not, add the first part, right click on it and choose Add part → Load for every other part)
• Assign extruders to respective parts
• Disable Wipe tower if you want, though I tend to use it, located at the edge of the printing area and with No sparse layers enabled, to move extruder away from the printed object before filament change and to prevent oozing after it
• Slice and print

Usually it is sufficient to do the color change in two layers, so with 0.2mm layer height you need to create an object of 0.4mm height embedded into a flat surface of the main object. Surfaces you can use are soundboard, back lid, headstock, fretboard and the back of the neck. I usually simply extrude a properly scaled and positioned SVG drawing and do a boolean cut with the main object, then export the parts as multi-part STEP or individual STLs.

You can of course use more than two colors, just add another extruder or two, but don't forget to keep track of the order of color changes (G-code preview/visualization in PrusaSlicer can help).

Non-printed parts

You will need ukulele tuning machines (I used Ortega OTMUKDC/OTMUKSTD) and soprano ukulele strings (I used Aquila Red Series 83U).

For the “truss rod” you need:

• M3x40 allen bolt
• M3x20 coupling nut
• M3x130 threaded rod
• M3 washer - 7mm outer diameter
• M3 washer - 9mm outer diameter

Assembly

Prepare the printed parts and fasteners. Roughen the surfaces that will be glued together (optional, but recommended).

Body

Glue body and lid together.

Glue on bridge. Use dowels to align it in place. This is the most important joint that will have to withstand the pull force of the strings, so it's best to use a good quality epoxy.

Feel free to swap these two steps if you find it easier that way.

Neck

Glue neck and headstock together. It may be necessary to sand down the mating areas a bit for a perfect fit. Use the M3x40 bolt with the smaller washer and the coupling nut to hold the parts together. It will be necessary to remove the bolt and the nut afterwards, so make sure you will be able to do it.

Sand down the headstock part of the fretboard area until the surface is perfectly flat and even.

Remove the bolt and the nut. Screw the M3 locknut on the threaded rod, just enough so when fully inserted together with the larger washer into the neck there is 10mm of it visible in the top pocket.

Insert the nut into the top pocket and fasten the rod so that there is 3mm gap on the rod side and 7mm on the other side.

Put back the bolt and tighten lightly.

Glue on fretboard. Use dowels to align it in place.

Wrap up

Glue body and neck together.

Insert the saddle.

The assembly is complete. Go ahead and install your tuning machines and strings.

You can adjust action by using higher/lower saddle. After initial tuning, check whether the fretboard is flat, if not, tighten the bolt at the headstock to compensate for the pull force of the strings.

Customization

Feel free to make any modifications you want. Changing bridge or headstock shape, or even sound hole shape (as long as the area stays the same) won't affect the sound, as well as decorating the soundboard or any other flat surface.