Abstract: An apparatus and method is disclosed for sensing material build-up, such as the undesirable build-up of cotton in a mechanized cotton harvester. A tube is mounted for eccentric rotation adjacent an area where build-up occurs, such as near a doffer. The tube is biased by a spring into one position and is eccentrically rotated against the spring by forces applied to the tube by accumulating material, such as cotton. A switch is mounted within the tube, and, as the tube rotates, the state of the switch changes in accordance with the rotation. A signal generated by the switch is used to alert an operator.