Ok, what I'm trying to do here is use the sketch on the top plane to remove material from the concave face outwards, leaving a 1mm rim around the window to it can be mounted in a case.

I've tried using a cut-extrude reversing the offset and choosing the side to cut.  Unfortunately, the only option is "through all", which is not what I want to achieve.  I need make a 1mm deep cut outwards...

If the piece part was flat, clearly this would be a simple planar face cut extrude...because the part is bent like a banana, it's giving me grief!

Either I need more sleep or more caffeine...my brain isn't working today and can't see the wood for the trees to solve this issue :/

Message was edited by: Jason Aspinall