Check that you haven't tightened the screws of the cutting heads too much, and make sure the the cutting heads are parallel and not crooked.
The correct position for the two blades are, the lower blade is marginally forward of the upper blade, but both MUST be parallel. The two screws which retain the blades together should only be turned until the screw starts to tighten then given a slight further tightening to secure them.
Davymac, July 2009
