Cutting a circular hole in a hollow cylinder without distorting the cylinder Whenever I try to cut out a circular hole in either a cylinder or sphere the polygons around the circular hole always have distorted normals after smoothing. Is there anyway to fix this. I've tried using the remesh modifier but wind up with some pretty ugly results.
you could use the Knife projection (in front mode of the circle ) 

select your cylinder and your circle  go into edit mode of your cylinder
and click while you are in Edit mode  in the T-panel on Knife Project