| 摘要 |
A drag bit excavating device comprising a core extending along an axis; a bit carrier supported on the core; cutter bits supported by the carrier along a three dimensional spiral having constant pitch and increasing radius along at least a portion of the axis, the carrier being relieved to provide radially extending spaces between the turns of the spiral; a frame supporting the core, carrier, and bits for rotation about and advance along the axis; and a drive to provide rotation, whereby the bits slot the material to be excavated while the material between portions of the resulting slot extends into the spaces to be subsequently broken away. |
