| 摘要 |
A lead screw tapping unit is disclosed wherein a tap or thread forming die is mountable on a tool support spindle which is longitudinally movable with a nonrotatable quill. The spindle is rotatably driven by a reversible drive motor and has a lead screw carried thereon which cooperates with a lead nut to effect controlled inward feeding and withdrawal of the tap relative to a workpiece. The lead nut carries a cam bushing which is operative to actuate a safety switch and deenergize a drive motor to stop rotation of the spindle should the spindle and tap undergo a thrust overload condition, or if seizure occurs between the lead screw and lead nut.
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