| 摘要 |
A chuck and drill bit combination for insertion into a front end of a percussive, down the hole drill forming a part of a cluster drill assembly, for selectively engaging and disengaging the chuck and drill bit during drilling operations includes the bit and chuck each having splines and grooves adapted to overlap and engage each other in a first stop position and further adapted to disengage from each other in a second stop position, whereby the bit is restrained from rotational movement but capable of axial movement in the first stop position and capable of both axial and rotational movement in the second stop position, to provide automatic indexing of the bit so as to position the bit's gage drilling buttons in a preferred position outboard of the drill centerline, to maintain maximum borehole diameter.
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