Hi Michael,

Clear ! Thank you very much for all these explanations.
Yes I watched your 3 video tuts, but maybe due to my bad English spoken understanding for sure some teached stuff you told was lost for me...
I am learning English spoken a bit more with audio books, so I hope this will be resolved soon enough O:-)

About what interest us here, I have almost what I needed except one : how can I bolean-cut perpendicularly to my inclined surface in my example ?
Say I need to cut the ellipse perpendicular to the side, but as you know my piece is not straight (surface is curved a bit) nor vertical

So what is the best and clever way to project my cutting bolean axis perpendicular to what I have to cut ?

Cordially,
Guy