Needed a presta to schrader valve adapter to fix my mtb flat tire. So I 3D printed one. Works well in a pinch but not for everyday use. Getting the threads and general fit on something this small is a challenge for most printers. Including my Ultimaker 3.
Designing the model was a bit of a challenge because Presta valves use a non-standard metric thread. Check out my blog post tutorial on how to create your own unique threads in Fusion 360.