Apparatus for drilling a hole having an undercut space

An apparatus for drilling a hole having an undercut space, said apparatus comprising:

• a shank;
• a first circular member fixed at its rear end coaxially to said shank;
• a stopper fixed to the periphery of said first member;
• a sleeve in telescopic engagement with said first member, said sleeve having an axial slot in slidable engagement with said stopper, said sleeve also having an inner flange forward from said first member;
• a drill spindle fixed coaxially to the front end of said first member, said spindle extending through said sleeve flange;
• an undercutter engaging with the side wall of said spindle slidably therealong through said sleeve flange;
• a second circular member positioned coaxially between said first member and said sleeve flange and between the cylindrical wall of said sleeve and said spindle, said annular member engaging with said undercutter to axially move therewith;
• a spring interposed between said sleeve and either of said undercutter and said second member to bias said undercutter and said second member rearward;
• a pair of pins fixed to said first member, said pins extending perpendicularly to the axis of said first member;
• a pair of cams supported rotatably by one of said pins, each of said cams having a pair of steps on both sides of the associated pin, said steps facing in the same direction;
• a pair of first rods extending axially through said second member, each of said first rods abutting at its rear end on one of said steps of one of the cams and at its front end on said sleeve flange;
• and
• a pair of second rods extending axially of said first member, each of said second rods abutting at its rear end on the other step of one of said cams and at its front end on said second member.