Dave,
Thanks for that detailed explanation, initailly my blades did hit the lower chrome edge of the frame, but I adjusted the blade position on the spline so they neither struck the side edge or the bottom edge of the screen frame. But then some time later they developed the clunk...... I was very aware of the locking screw coming loose and always used blue locktite. I'll get Matt at Life's to have a good look at what is going on.
Again many thanks for taking the time to respond and the detailed explanation
