Cutting holes in thin surface

[BrianO]

I'm modeling and visualizing a performance space from the interior; the space has a barrel vaulted ceiling that is to have windows cut into its side through the curve. Up to now I have used the ceiling as a polyline pulled to be an extrusion with zero thickness and it's exactly what I need. (need to have an open interior)

In a trial of cutting holes into the 3D ceiling, it only worked the first time and subsequent operations turn the ceiling surface into a solid. I'm using the Push/Pull tool in Sub-Face mode to make the cuts. I'm not sure why I can't repeat the results from my first attempt, that has two windows and circle and square pulled through the thin, non-solid arch. File attached. I don't know that anything changed in my process.

How do I prevent solids in this operation?

thanks.

Brian

[bcd]

You can shell your ceiling by a small amount (1/4") and then perform the subtractions.

An alternative is to extract Nurbs Surfaces from the completed ceiling.

[Jonathan Pickup]

I think that's a bit of a bug (or just the way its designed to work, because it does the same thing if you extrude the shapes and use subtract solid.

If you shell the main shape first, then you can subtract the solids and keep the shape.

[Kevin McAllister]

Extruded shapes used as surfaces with zero thickness often misbehave in my experience. If you want to keep the zero thickness surface, convert it to NURBS and use the project tool to cut the window holes. It is better behaved.

Kevin