Cutter head for pit-boring machine

A cutter head for a pit boring machine which is employed in reverse circulation drilling, comprising:

• a hollow open-ended main shaft;
• a pilot cutter at one end of said main shaft;
• supporting members spaced at intervals around said main shaft and each having one end fixed to the circumference of said main shaft and extending radially of said main shaft and away from said one end of said main shaft at an angle .alpha. relative to a line perpendicular to the axis of said main shaft and at an acute angle .beta. to the axis of said main shaft;
• a stabilizer at the other end of said main shaft and connected to the outer portions of said supporting members;
• gauge cutters on the outermost ends of said supporting members;
• and
• cutters attached to said supporting members at intermediate positions between said gauge cutters and said main shaft, said cutters comprising rotary cutter means rotatably mounted on the supporting members and drag cutters fixedly mounted on said supporting members, said rotary cutter means and drag cutters lying along a spiral line along a conical plane defined by the edges of said supporting members facing toward said one end of said main shaft and extending from the outer ends of said supporting members to said main shaft, said rotary cutter means each being at least one disk having teeth on the circumference each having the ends toward said one end at a distance from the supporting member on which it is mounted which is greater than the distance between tips of the drag cutters and the supporting member on which they are mounted, said rotary cutter means each having the axis of rotation at an acute angle .theta. relative to a radius perpendicular to the axis of said main shaft, said angle lying in a plane perpendicular to the axis of the cutter head.