I am having a difficult time trying to edge joint some 8' boards. I'm not able to get as straight of an edge as the shorter pieces that I normally joint. I tend to get a cup in the middle. I am sure this is because of my technique. My table length is 59" and I have a 40" long fence that is 6" high on my jointer.
Is my difficulty the nature of the longer boards?
What can I do to improve my results?