Creating spherical holes with subd

Rhino
1

Hi all,

I can’t quite work out how to get perfectly circular holes in subd mode.
I’ve tried slightly extrude the center, and scaling the resulting face, then extruding into the opposite direction (apologies for the lack of technical terms), as below:

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The only issue with this is the holes/dents appear somewhat rectangular and do not have the sphere like quality I am after.

2
3

Thanks for that video, it was quite insightful - However, it doesn’t seem to work too well if you aren’t using a flat surface. This ellipsoid has a convex surface and doesn’t seem to respond too well when I try that method.

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image1881×681 331 KB

4

I was actually able to use the control points to turn my original subd dent circular, so that worked quite well!