Hi to all, i need to make a simple offset cut on my curved surface, i usually do that in this way:

1. Project a Split Line of your sketch onto the surface (Insert, Curve, Split Line… Projection)
2. Offset (Copy) the Split Faces a depth of zero (Insert, Surface, Offset…)
3. Cut-Thicken each open profile (Insert, Cut, Thicken…)

The problem that i have is that the offset copy is not perpendicular to the surface as you can see in figure, so the cut will be skew...

Can anyone help me?