Morphed objects?

[DaveR]

This sort of question comes up often. A search will turn up a number of threads. Start with these:

Reducing square duct to round duct

I have a square duct of 20* 20 mm outer dimension whitch I want to reduce to a round duct of 10 mm outer diameter via a kind of elbow bend. Both ducts have a wall thickness of 1 mm. Is it possible to do this by means of the extrusion tool, follow me tool or else way?

Push/Pull a circle from a rectangle

Gday guys just need a little help here. I would search but don’t even know what terms I would search for. Basically, I want to create a headlight bucket for an RC car I’m going to get 3d printed. The rectangle will be the top (18x22mm) and dropped about 5mm below the rectangle will be an 18mm dia circle, nice and centralized to the rectangle. Hopefully you can see this from the picture. Question is, how do I stretch or whatever the term so I have a surface, so it would look kinda like funnel …