A burr is a raised edge or small pieces of material remaining attached to a workpiece after a modification process. It is usually an unwanted piece of material and when removed with a deburring tool in a process called 'deburring'. Burrs are most commonly created after machining operations, such as grinding, drilling, milling, engraving or turning. It may be present in the form of a fine wire on the edge of a freshly sharpened tool or as a raised portion of a surface; this type of burr is commonly formed when a hammer strikes a surface. Deburring accounts for a significant portion of manufacturing costs.