It would be helpful to add a “OnSurface” option in the command line upon drawing a circle object. Also, a centermark helper could be temporarily placed in the exact middle of the picked surface to make it easier for the modeler to build a circle in the ideal position. This is mostly useful for people working on architectural projects or mechanical parts for CNC-machining.
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Hi @Rhino_Bulgaria,
Try the attached script.
circOnSrfNormal.py (1.1 KB)
There is a point instead of a centermark cross.
Rhino’s “Point” needs to checked in the Osnap menu.
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A macro may help for now -
! CPlane Object Pause Circle Pause Pause CPlane Undo
-Pascal
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Wow, this works on freeform surfaces as well. Really handy for situations where a hole must be created normal to a complex panel. 
@pascal Pascal, your macro also works, but it performs best on flat surfaces since it’s based on plane approximation and flat surfaces naturally have a predictable CPlane.
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