| 摘要 |
A support and positioner for a rock drill has an extendable and retractable feed boom pivoting about a pivotal support arranged laterally below the axis of the feed boom, so that when the boom is swung downwardly to maintain a desired line of advance of the drill, the boom rocks forwardly so as to increase axial drilling thrust and the extent of forward movement of the drill, and reduce the bending stresses imposed on the drill steel.
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