Armature Deform with sharp limits I have a requirement to rotate part of an object, leaving other area intact, so have created a bone and defined the vertices belonging to the bone. Since the part to be rotated is very sharply delineated I am using manual vertex assignment. However, when the the part is deformed some portion of another part of the object is also getting deformed, which is not desired. I tried setting the paints in the weight paint mode, but here also the brush either includes the unwanted portion or subtracts from the part itself. 
A related query is: I have seen highlighted lines extending from vertices to neighboring vertices, that seem to be indicating weights (or influences? not sure...  I am new to blender). What's the logic of applying these weights and is there a way to change them? They are sometimes seemingly arbitrary. In the attached figure for example, A influences B and F but not C. Why? And how, if at all, to change this influencing?
I found a workaround: 
1) In edit mode, select the vertex group assigned to the bone and hit P to separate the selection from the main object
2) remove the vertices from the main object that belong to the bone (there's actually just one in this case)
3) In object mode select the main object and the separated one and hit ctrl-J in order to join them. Now if I select the vertex at the tip of the part to be moved, there is no influence shown to the main part vertices. Maybe there is a double vertex at that position, but that doesn't create any problem for me for now.