I redesigned a tool which helps you to tie up a balloon. My girlfriend found a picture of something like this online. I redesigned the modell by myself in SolidEdge ST10 Education.
I printed with support, but if your priter is dialed in well, you won't nessecary need a support structure.
If you want to remix or to customize my balloon knot device, feel free to use the SoldEdge Education .par file, which also uploaded.
Knothilfe.par | 512.0KB | |
Knothilfe.stl | 386.7KB |