Quick Fillet is a simple tool for making curved surface (quads) by using cross section edges.

It use edges from 3 orientations to calculate the rounded surface.

The requirements are :

1. The number of edges has to be even (2, 4, 6, 8 ...).
2. Select 3 set of edges. Although they can be any orientation (they can be flat.... the tool will not error ! ),
   for the best result, they should be representing 3 directions.
3. The number of edges has to be the same for all edge set. So let say if it is 4 edges on one side, it should be 4 + 4 + 4.
4. The tool will automatically determine the separation of edge sets, by using "sharp angle".
   The sharpest angle locations will be used for edge sets seperation.
5. If separation is not correct, you can change it by using the offset index in menu (lower-bottom screen).

To completely create a "rounded head" for cylinder or any mesh, theoretically it need 4 fillets.

And theoretically you can use it to fill a flat triangle.....

Usage

Blender Edit mode >

Right click in the 3d viewport , select Quick Fillet at the bottom of the blender's context menu.

Updates

Version 1.2.0

• Fixed a calculation bug that cause symmetrical errors.

Version 1.0.1

• Fixed the face normals and minor bug

That's it ! : )

It is a free addon. Hope that it is useful for you !

https://x.com/kushirosea