Solidify problem with borders 2.79 I take a circle, extrude it, and solidify and obtain a kind of cylinder.
If I deform the cylinder, the border becomes skewed.

How can I have a flat border as if the cylinder was cut with a knife?
You can solve this easily in Blender 2.82+.  

In the Solidify Modifier


Set Mode to Complex.  
Set Boundary to Flat.