I just started getting a ragged cut the past few days. This is the 4th season for this set of blades and the lifts are badly worn. I had gotten lazy and had been sharpening my blades on a steeper angle to save time. I took an hour and reground the ~30 degree angle and am now getting two strips where the outside spindles are. The center is a good cut. Do you think new blades will cure this or is it more serious, like a slipping belt?