| 摘要 |
<p>A boring device (10) is used for producing undercuts at the end of holes drilled in masonry, concrete or rock. It has a rotating shaft (12) with a central bore (38). There is a cutout portion (14) containing a rocking lever (18a, 18b) on a central pivot (16). The lever has a cutter (20) at its lower end; the lower end of the lever is forced outwards by a sloping surface (28) on a plunger with a conical end (36) which is pushed against the end of the previously drilled hole. A spring (22) returns the lever to its non-operative position when there is no pressure on the plunger.</p> |
