| 摘要 |
A drill rig includes a main engine which drives a drilling spindle through a clutched transmission. A protective cage surrounds the spindle when the transmission is in gear to prevent workmen from being injured by drilling tools. An auxiliary drive motor operates the spindle for a limited number of revolutions when the transmission is in neutral and the protective cage is open to permit workmen to rotate the spindle to add and remove augers, couple and uncouple drilling rods, and perform other necessary tasks.
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