This is a remake of Hiroko Price's funnel (kitahiro921). Her design is great, but seemed just a bit fragile to me. Besides, I wanted to learn how to design something like this in FreeCAD, so I created my own version. The wall thickness on this one is around 1.2 mm, a very small increase over the original but enough to make it a bit stronger (on my printer, anyway). I also added a small lip to the top to make that edge a little bit more robust.
Thank you so much Hiroko for the original design, and for allowing me to post my version of it. Also thanks to Duncan Gunn (DigitalDunc) for posting the FreeCAD file for his Offset Funnel. You inspired me to post the source file for my designs as well.
The wall thickness was adjusted so it prints well on the MG M3 with a 0.35 nozzle, with the extrusion set to Auto. With something this thin, getting the ratio right is key to having it print well and having decent strength. If you need a different wall thickness, I've included the FreeCAD source file, or drop me a note and I'll try to help.
Designed in FreeCAD using Loft and Cut
Designing this was a learning process for me, I had not used Loft before. What fun! It's a very easy way to create shapes like this. If you are a FreeCAD user, I've included the "source" file.