Down reaming apparatus

An apparatus adapted to be attached to a drill string, said down reaming apparatus having a frame and a rotatable cutterhead, said down reaming apparatus comprising:

• an upper stabilizer having an upper stabilizer hub adapted to be oriented around the drill string such that the drill string is rotatable relative to said hub, and a plurality of wheel assemblies radially attached to said upper stabilizer hub, each of said wheel assemblies having a compressible wheel means adapted to be oriented against a bored hole wall and a rotatable overload wheel means having a radius less than that of said compressible wheel means such that said overload wheel means is oriented against the bored hole wall upon compression of said compressible wheel means;
• a weight assembly having a plurality of plates stacked in a plurality of layers, each of said plates having a plurality of tie rod openings, a plurality of tie rods adapted to be placed through said tie rod openings of said plates, and means for securing said tie rods to secure said plates on the frame of said down reaming apparatus such that loads from rotation of the cutterhead are into said weight assembly;
• and
• a lower stabilizer having a lower stabilizer hub having an inner race attached to the cutterhead and an outer race rotatable with respect to said inner race, and a plurality of wheel assemblies radially attached to said lower stabilizer hub, each of said wheel assemblies having a rotatable wheel on a wheel support and a compressable bumper between said wheel support and said lower stabilizer hub, said wheel support being pivotally connected to said lower stabilizer hub whereby reaction of said wheel against a bored hole wall causes pivotal movement of said wheel support against said compressable bumper.