In one aspect of the present invention, an expandable tool for an earth boring system comprises a mandrel with a sleeve positioned around the outer surface and a blade disposed in a slot formed in the sleeve. The sleeve is also configured to slide along the tubular body. The blade comprises an interior slide groove located on an interior surface and an exterior slide groove located on an exterior surface. A sleeve protrusion is configured to extend into the interior slide groove, while a mandrel protrusion is configured to extend into the exterior slide groove. The blade is configured to shift laterally out of the slot as the sleeve slides axially, wherein the interior and exterior slide grooves are oriented at different angles and as the sleeve slides axially along the length of the mandrel, the slide grooves lock the blade in a pre-determined position through a wedging effect.