Because our knives are made of high-carbon/high-chromium forged alloy tool steel, they can go significantly longer than the knives on most "bargain" chippers without sharpening. Still, as with any cutting tool, keeping a sharp edge is important for maintaining peak performance. When the chipper starts to "bog" down, and/or vibrates and requires that you regularly force the material downward into the chipper chute, it's usually a sign that the knife is dulling. Many customers choose to get an extra knife to have on hand. That way, you can keep working with a minimum of downtime. The replacement DR Chipper Knife Kit comes with all the necessary hardware. Hardened steel knife Hardware Please refer to your owner's manual for sharpening and installation instructions. Please call us toll-free 1-800-687-6575 if you have questions about your DR. TIP: If chipping a lot of soft wood (pine, spruce etc.), and pitch build up is observed on the knife, it is recommended to occasionally chip some hard wood to clean the pitch off the knife.