Using Ruled Surface as parting line for face draft

[Anonymous]

I have a stamping die detail where I need to start the draft angle 6.35mm from the surface.  This in initially was sent to me as a .stp file.  My issue with the top surface of the part having various contours.  I cannot get any function to work where I can create a parting line that is 6.35mm down in the Z axis AND also following the same contour as the surface face.  I was able to get a ruled surface to create a sort of parting line where I'm trying to start the draft angle but am stuck from there.  I'm using Inventor Professional 2020.  Thank you for any help/advice given.

[johnsonshiue]

Hi! I took a quick look at the part. First, the solid body is a bit far from the origin. I relocated it back to the origin. Second, Ruled Surface may not help this case to create the parting line. It is better to use the base surface. I used Delete Face -> Heal to remove the cutouts. The surface becomes very smooth.

Please take a look at attached part and see if Face Draft works more desirably.

Many thanks!