The main difference between a grinder and a sander is that they are generally designed for different tasks. Grinders are designed to cut through the material instead of removing material. This makes grinders ideal for people who want to remove large amounts of material in order to expose the grain of the wood. Although specialized grinders are capable to cut, shape and carving different types of material. Sanders, on the other hand, are designed to level out surfaces and smooth away light amounts of material in order to create a uniform surface. Sanders work well for people who want to clean up an untouched piece of wood. Sanders typically have a lower speed than grinders and are used for lighter sanding tasks such as preparing surfaces for finishing. They have a softer pad that conforms to the surface more, which leads to less scratching. Sanders also come in random orbit sanders which move in random patterns and don't cause swirl marks.