Hi Ron,

Here is how BVM do it at, 3.45min.
https://www.youtube.com/watch?v=qHi8PtEbvsI
Actually the video doesn't show too much detail of what is laid underneath the hinge "cut".. There is a strip of Mylar laid in during moulding. this strip of mylar becomes the hinge .The trick ,and skill of the builder/factory worker, is to cut through the glass/balsa layers, without cutting the Mylar..