Extract hole feature from 3D model

Hi, I have a 3D model of a part that includes a number of holes. I need to machine these holes using RhinoCAM, but I somehow have to extract the boundary of the hole? I have a number of holes and selecting each one and extracting the curve is taking a long time. I’m new to Rhino and would like help to be able to machine these holes without too much work?

graham, _DupFaceBorder is what you want I’m pretty sure.

Hi carve cream, thanks for the tip, will give it a go