Glen, the porter Cable applies the pressure directly like most blade clamps do. the DeWalt has an extra part in between the screw and the blade.
Uh-huh, that's what my pic and diagrams clearly show!
Those always have at the end of the arm a screw going through and that one is about 1/2" away from the end of the arms:
Except in the case of the Craftsman I had before my Porter Cable, which by the way also squeezed the blade. The thumbscrew didn't contact the blade at all.
Anyway, my point here is that I solved my problems with spiral blades on my Porter Cable saw. In my case it didn't have anything to do with sanding the thumbscrew or the grub screw (which I did do to help keep blades from slipping). Even with them sanded, the thumbscrew was still twisting the ends of the spiral blades 'til they snapped. It wasn't a matter of too much tightening, because if I didn't tighten them that much, I couldn't get any real tension on the blade. If I'd had some Delta/Dewalt thumbscrews, life would have been much easier, but I didn't know they were setu up that way.
So, caselman74, take whichever advice you choose. I can tell you that if I had to do it again, I'd order some thumbscrews from Delta or Dewalt.