This is a common conical funnel that can be modified easily in OpenSCAD to generate whatever custom settings are desired.

This was my first attempt at creating a model from scratch in OpenSCAD and my first time properly using variables and modules.

Using OpenSCAD, you can set the following parameters:

-Length of the tube ( small end )
-Height of the the funnel cone
-Wall thickness of the entire model
-Diameter of the top of the funnel
-Height of an optional 'lip' at the top of the funnel
-overall model smoothness