I used to rarely ever change them, but eventually it started cutting such jagged lines that I was wasting fabric, so I caved and bought new ones. Oh, wow, was I ever happy!!! Since I do a lot of small pieces for applique on my quilts & basically only use my scissors to cut the backing fabric, it ends up that I change it out for every yard or so of quilt. Soaking my cutting mat helped them last a bit longer. Wish I'd known that trick earlier on since some of the cut marks don't come out (prob also due to using such a dull blade that I had to apply a lot of pressure to get my cuts).
I figure I change my blades on about the same schedule as my needles -- every 8 hours or so of use.
Oh, and btw, I have a 28mm Olfa. It came in some quilting kit I got years back & I haven't seen the need yet to move up to the next size, but that probably affects how often I have to change them since my blade has to go through 2-3x the number of rotations of the larger rotary cutters.
Last edited by Bree123; 07-24-2014 at 10:00 PM.