My laser programmer and laser operator are struggling with cutting straight parts. The parts are 11ga CRS 3"x 30" rectangular blanks. When they pull the parts they come off in an hour glass shape. The mid section of the blanks are about .025" smaller than the ends. From my 20 yrs experience I only remember banana shaped parts. We are cutting out of a 48" x 120" sheet, we are using nitrogen for clean cutting. Any help would be great.