When it comes to custom parts for musical instruments, Big Blue Saw is the top choice for the instrument makers and musicians in the know. Over the years, we've made specialized guitar capos, sitar bridges, replacement accordion parts, and much more.
I've never seen an entire musical instrument using waterjet cut parts, though, so I set out to create one. After considering several possibilities, I decided to build a simple thumb piano. A thumb piano consists of a set of tine each tuned to a different note. When plucked, the sound of each tine resonates in a chamber to amplify the sound.
I started by using the free xylophone bar length calculator from Windworld. I input the longest bar length of 4 inches, and the calculator spit out the lengths of all the bars such that they would form an octave plus one higher note. The shortest bar was 2.83 inches accoding to the calculator. From there it was easy to design a "comb" with the various tines.
Next, I needed a resonating chamber. The best way to do this with waterjet cut parts is via the stacking technique, described in its own article. I designed a plain flat piece for the bottom, pieces with cavities for the middle layers, and a top with a resonating hole for the sound. I added holes so that I could bolt all of the pieces together, including the comb. Finally, I added two more small spacer pieces so that the comb could rest slightly elevated from the top of the resonator.
With this design, I could use just about any material and thickness that would be stiff enough for the tines to vibrate. I chose 1/8" thick aluminum 6061 alloy as it's relatively inexpensive and this was just a prototype instrument, after all.
After the parts were waterjet cut, I bolted them together using #10-24 machine screws.
Now it was time to play. How does it sound? Check out the video below.
OK, it's a little out of tune. This is partly due to the calculator I used being designed for free floating xylophone keys, not tines which are all connected on one end. The higher notes sound more musical than the lower notes, so if I had to do it again, I'd start with the longest tine being around 3 inches. I would also consider using more and thicker bolts to hold the case together, as I noticed sublte rattling of the layers when the notes are struck. Plucking one note can cause the others to ring a little bit, so I would change the design to isolate the notes a little better, perhaps by using multiple combs. Finally, brass might make a better choice than aluminum for the material, as it's a more "musical" metal.
If you've got any more ideas for improving this thumb piano, let me know in the comments section or by e-mailing firstname.lastname@example.org.