I should draw the rib between these two cylinders. Can someone tell me how to make sure that the upper edge of the rib fits perfectly with the edges of the cylinders? Thank you.
I think you could do it in two ways, as long as your software allows you to:
build a surface (a line) that has as edges the initial and final arc segments image1
1) Extrude image surface2
2) Use the surface to cut an image extrusion3