It may not be caused by a dull rotary blade afterall though continued use will have that result. The next time you pick up your rotary cutter - take a moment to dismantle it and to look closely at the shaft of the holding screw. I was having 'sudden braking' and 'jerky starts' while using my frequently used Fiskars rotary cutter - it was oiled, delinted, and blade changed - but the problem continued. Closer inspection of the various parts showed me several deep scores in the screw shank (the part that goes through the head of the cutter and the blade opening). Over the years, the blade action has scored a line around the screw shank and the inside edges of the blade are now catching in this groove - the blade suddenly stops rolling and brakes roughly! If you do see any sign of metal shavings around the opening of your rotary cutter - then check out the screw shank and consider replacement. Jennifer in Ottawa