We recommend changing the blade on your Omnigrid® rotary cutter often. In fact, it's ideal to change it every time you start a new project. If you are using a heavier or lofty fabric in your project, you may need to change it more frequently. A sharp blade will make your rotary cutting easier and more accurate. It will add to the life of your mat, and because it cuts more smoothly, it is a safer alternative to a dull blade.