Abstract: A starter mill adapted for use with a whipstock to mill a window through the casing of a well for deviating the direction of drilling. The starter mill includes a bearing nose which is utilized to indicate completion of the milling process. As the mill nears completion of the milling process, the bearing nose will become wedged between the whipstock face and the casing preventing further downhole movement. The bearing nose will engage whipstock and casing, allowing the work string to continue to rotate although the decreased torque resulting from the absence of milling provides a clear signal that the milling operation is complete. The cutters of the mill are spaced a predetermined distance from the bearing nose to ensure completion of the casing window.

Abstract: A section mill for cutting through well casing, the mill including multiple sets of cutting blades which are selectively engaged to continue cutting operations as blades dull. The cutting blade sets are selectively indexable such that as a first set dulls or fails a succeeding set can be utilized following retraction of the first set. The section mill includes a central mandrel having offset cammed surfaces which engage the cutting blades and cause them to expand outwardly. The mandrel is axially displaceably by a piston affected by hydraulic pressure. As the mandrel is axially displaced the indexed cutting blades are expanded by the cammed surface. Indexing is accomplished by a cam drum which allows the mandrel to be rotated relative to the cutting blades in order to align the next cammed surfaces with their respective cutting blades.