Gear rack for a mining machine

In combination with a mining machine adapted to move along a conveyor, a rack comprising a plurality of rack segments supported end-to-end for limited lengthwise movement along the conveyor, said mining machine including a drive means having spaced-apart spur gear drive wheels for meshing with gear teeth on opposite sides of said rack segments each of which comprises an elongated rack body having a rectangular cross section with arch-shaped upper and lower surfaces along the length thereof, opposite end portions of said rack body having a vertical hole along the height thereof intersecting a horizontal hole extending across the width of the rack body within a horizontal plane of symmetry thereof, and attachments projecting at uniformly-spaced intervals from opposite lateral sides of said rack body and rigidly attached thereto symmetrically with respect to said horizontal plane of symmetry, each attachment having involute toothed flanks extending upwardly and downwardly from said horizontal plane of symmetry such that inverting a rack segment 180.degree. relocates downwardly-extending toothed flanks of the rack segment to extend upwardly for driving engagement with said spur gear drive wheels of said mining machine.