Customisable, parametric 3,4, 5 (or more) sided funnel

VERY IMPORTANT.

The STL files that this generates give a solid object which isn't much use as a funnel. To get a hollow funnel, your slicer settings should be NO TOP and BOTTOM LAYERS, NO INFILL and 3 OR MORE PERIMETERS (SHELLS).

Sometimes a circular funnel is no good if you need to get in a tight space or want it to fit unobtrusively in the corner of a planter for example. This code will make a triangular, square, pentagonal or whatever sided funnel you want.

There are only two variables you need to input, the size (width) and how many sides (3 for triangular, 4 for square, 5 for pentagonal etc. The higher this number, the more "round" the funnel will be. All other dimensions are derived from these two inputs although if you want, you can play around with the Open Scad variables to alter the other proportions. The height will be about 95% of the width so if you maximum print height is 150mm, don't make the width any more than this.

Note that this uses the $fn function of Open Scad to limit the number of sides of a circular object. Therefore, the width you put in is actually the diameter of a circle which will touch the corners of your funnel. So, if you wanted a square funnel that was 100mm across the flats, you would need to multiply this by about 1.4 which will give 140mm across the corners.

I've included a few stl files as well as the Open Scad file to give some idea of what is possible.