An OpenSCAD parametric funnel with some options like

• outer diameter, stem diameter, stem length, cone angle
• air gap (so air can escape while stuff flows in)
• “turbo” fins (number, angle, depth), also good for holding filtration paper away from the funnel walls

This is a vase mode model, so it needs only a few grams of filament and prints fairly quickly. If a funnel gets messed up beyond cleaning, not much plastic is wasted.

Printing:

• use vase mode
• set extrusion width to 0.7mm (or more) for stability (0.4mm or 0.6mm nozzle)
• set bottom layers to 0

A note on “turbo” fins

I'd like to comment on those turbo fins: I consider them mostly useless. Some think that a vortex speeds up flow, but that is true only under some conditions: e.g. to get water out of a bottle. The vortex forms a stable air channel in the center, so air can get in while the liquid pours out. Without it the rising air bubbles get into the way of the falling liquid. The same problem can arise when funneling some liquid into a bottle and the funnel covers the whole bottleneck. Then a vortex can help – if it is strong enough to indeed form an air channel. I've seen “turbo” funnels, where those ‘turbo’ features are way to shallow to bring the vortex up to speed, and most design's vortex fins actually get very steep near the bottom and thus slow down any vortex motion…

If the funnel does NOT close up the bottle neck, air can escape at the side, and a vortex is not needed at all. Actually it's counterproductive, as the centrifugal force counteracts the water getting down.

My conclusion: If your funnel can block the bottleneck, use a funnel with a built-in air gap.

However I implemented turbo fins for 2 reasons:

• For you to try out if they actually can help funneling. I also implemented a version with fins that do not get nearly vertical near the bottom.
• These fins can be useful for filtration. They keep a gap between filter and funnel wall and thus allow already filtered liquid coming out at the side to easily flow down. Many coffee machines use those fins, too.