3D printing is used here to transform an abandoned portafilter into a small stringed instrument. The electroacoustic mini-instrument can be plugged into an amplifier for control of gain or added effects. In this tutorial you can see how to make the most simple version. The first step is to find a a discarded portafilter (preferrably the kind with a hexagonal cavity in the back of the handle)
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Step 1: The Portafilter
I discovered a bin of discarded Portafilters from expired espresso machines at Alan Steel in Redwood city. They reminded me of miniature banjo frames. I decided to make appendages to transform this transporter of coffee into a transmitter of the plucked string.
Other components required:
access to a 3D printer or printing hub
Steel dowel pins (size: Metric Type 316 Stainless Steel Dowel Pin, M3 Diameter, 28 Mm Length)
Piezo Disc with wire leads
3.5 mm phone jack
3.5mm audio cable
a small zip tie
Step 2: Soundboard Wrapper
If you happen to find a portafilter of the same dimensions as the one here, you can download the attached STL files and print the components. The little sound board will fit snug over the filter cup turning it into a small resonant chamber. The neck fixtures into the cavity in the back of the handle. These may vary so you may have to redesign your own models to fit your portafilter.
Step 3: 3.5mm Audio Connector
If you can find this model of portafilter you are in luck. Because the 3.5 mm from Philmore perfectly press fits into the coffee outlet. Sometimes there is luck!
Step 4: Insert Frets
7-A4 dowel pins make great press fit frets. The equation (remaining distance to saddle/18 for the next fret distance) for fret distances is used to separate these slots in the CAD model.
Features may vary on the protafilters. The ones I found had differing orientations in the hexagonal cavity in the handle. This required modifications to the cad file such that the neck was aligned with the sound board.
Step 6: Assembly
Attach the piezo disc to the audio jack inside the portafilter. Plug the microphone into an amplifier to test it. If the connection is clean, glue the piezo behind the sound hole on the underside of the soundboard.
Step 7: Bridge
You can use a small piece of wood doweling as a bridge. Or you can print one with the attached STL file.
Step 8: Tuning Pegs
1/4 sized violin pegs are required. Two of them should be shortened so that their turning knobs do not collide when turning. Tuning pegs often come with a string hole. This will likely be too far out for this instrument. Alternate string holes must be drilled into the tuning pegs closer to the turning knob. Tighten the strings while firmly applying pressure on the peg into its hole.
Step 9: String Up the Javalele
Tiny channels are provided in the model to guide the string to its respective peg. On the bridge side, the strings can be tied as you would a classical guitar.