Thanks Michael. I put everything back on the default style and tried it with the selection box. For me it cuts all the way through rather than creating a pocket. Why?

If I do it the way shown in your second video then it works as expected.

Video is here, file is attached:

https://www.dropbox.com/s/yr3f31id7zwx47k/CutThrough.mp4?dl=0

Also what did you press in your first video to switch to polygon rendering?

Andy