Summary

I used pfh's excellent sopranino as a starting point. In the end, I only kept the original fipple, but having a functional and in-tune starting point a fifth down was invaluable.

On a well-calibrated printer it prints nicely in PLA upright without supports. I added a brim to ensure it didn't get knocked loose during printing. There are some non-trivial bridges at the block and fipple windway, but if axes & extruder are cal'ed and temperature is tuned, it's doable. I used 30% infill. Ensure that your extrusion is good and your filament is dry to achieve an airtight print.

It's fairly in-tune. Fingerings are a bit different than on soprano recorder, but can be found here:
https://www.mollenhauer.com/en/service/fingering-charts

2024-11:
I've attached a fingering chart for the best-intonated fingerings I've found for this recorder. I hope to revise the design to improve intonation further in the future.

2024-03-24 update:
-Spectrogram of a scale recording on this recorder with the target pitches overlaid in dashed lines.
-OpenWIND plot of the bore & vent admittance function for some of the fingerings has been added.