OpenSCAD sourcecode coming soon. Please note that this is an four tone instrument not a signalling device. Instead of blowing in with full force you should find the correct amount of air for each tone. Several of these whistles where printed on the Linuxwochen event (2015 in Vienna Austria) http://www.linuxwochen.at/wien/ This whistle design is based on some accumulated experience. The gemstone shape naturally emerged due to the design restrictions. I found that sound quality (lack of airiness) strongly depends on the used filament. (I used 0.1mm layer height and 30% infill) Btw: FDM ... fused deposition modelling - if you didn't know yet