@ Andy

The flange itself adds a lot of strength to the board. By the way, my next project is to print a back for my 5 X 7 Linhof Kardan Bi. I've lost track of my 5 x 7 to 4 x 5 reducing back so just for fun I thought I'd try to print one - I'd have to make it in two pieces due to the size. I have a couple of 4 x 5 Technika backs floating around here so all I need is the square plate and light trap.