| 摘要 |
An apparatus for controlling the forward and return movements of a drilling spindle operated by a primary actuation element which determines the forward speed and the total forward stroke of the drilling spindle. A plunger assembly operatively connects the primary actuation element with the drilling spindle. Reversing valve means act via the plunger assembly upon the drilling spindle for initiating its rapid forward and reverse movements. Means are provided for triggering forward movement of the drilling spindle during a portion of the time that the drilling spindle carries out its rapid return movement, said means including adjustable means for selectively determining the point in time during rapid return movement of the drilling spindle that its rapid forward movement should be initiated.
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