Thanks Kevin.
Might have found the problem, a build up of gunk in the top of the bladeholder. It was allowing the blade to slip past the stop, therefore the tension was off every time it slid passed needing more force on the screw to hold the blade, more tension more force on the screw....
It's been ok since, a little bending on #2.0 blade but not bad. My father in law has a small machine shop ( before he retired he was a toolmaker) and I'll get him to turn the ends flat, maybe see if he can replicate the spinning ends.