Underreamer with adjustable arm extension

摘要

An underreamer having an adjustable arm extension includes a cam for urging the arm outwardly in an opened position, and a stop pin which engages a slot in the arm for limiting the maximum arm extension. An insert for the arm has a surface which overlaps a portion of the slot to establish an effective length for the slot. By changing the configuration of the surface on the insert, the arm extension can be adjusted.