Expandable raise bit

Claim 1

A raise bit for enlarging a first hole into a larger second hole by being drawn through said first hole and disintegrating earth formations surrounding said first hole, comprising: a drive stem; a raise bit body connected to said drive stem, said drive stem defining a bit axis of rotation; primary cutter means positioned on said bit body for disintegrating the formations out to a first radial distance from said bit axis of rotation; secondary cutter means adapted to be connected to said bit body selectively located in a first position for disintegrating the formations between said first radial distance and a second radial distance from said bit axis of rotation, said second radial distance being greater than said first radial distance, and selectively located in subsequent positions for disintegrating the formations between said first radial distance and subsequent radial distances from said bit axis of rotation, said subsequent radial distances being greater than said second radial distance; and expansion means adapted to be located between said secondary cutter means and said bit body for locating said secondary cutter means in said subsequent positions.