| 摘要 |
1466962 Arbors E D HOUGEN 22 Feb 1974 [26 Feb 1973] 39190/76 Divided out of 1466961 Heading B3C [Also in Division B5] An arbor for an annular hole cutter comprises a shank member 32 having a forward end for supporting a cup-shaped annular cutter 14 which cuts a circular groove through a thick workpiece and forms a round slug within the cutter, the shank having a central bore 34, a pilot member 124 axially slidable in the bore and having a drill point 126 and a shoulder 128 adjacent to, but spaced axially rearward from, said drill point 126 wherein the pilot member is held in an axially forward position by a spring 70 to project the drill point forwardly of the cutting teeth 58 of the cutter 14, and is characterized in that a yieldably resisting retraction means, e.g. a spring and ball detent 136, 138, resists retraction of the pilot member within the bore 34 until the retraction force exceeds a value in excess of that required to cause the drill point to cut a pilot hole in the workpiece and thereafter permits axial retraction of the pilot member at a force substantially less than said value. In operation as the arbor is advanced towards the workpiece the drill point does not cut a hole under the influence of the spring 70 only. When a shoulder 134 engages the detent ball 136 an axial force is generated to produce cutting by a drill point. When the shoulder 128 engages the workpiece a higher force is generated to overcome the spring detent so that further feed of the arbor continues with a reduced axial force on the pilot member and no further drilling takes place by the drill point 126. |
