| 摘要 |
<p>A drilling assembly includes a drilling tool having a shank and a drill bit at the leading end of the shank and having cutting edges. The assembly further includes a collar adjustably and arrestably mounted on the shank, and an abutment member having a central passage into which the tool element is received at least during terminal phase of the drilling operation. The collar has a convex contact surface, and the abutment member is formed with a depression bounded by a concave contact surface, the two contact surfaces sliding on one another when the tool element is pivoted to form an undercut hole in a support structure. The abutment member abuts against a surface of the support structure around the open end of the hole, and is prevented from rotating with the tool element either by pins which penetrate into the support structure, or by a layer of friction-retarding material, such as rubber, interposed between the abutment member and the surface of the support structure. The abutment member may have a tubular centering projection receivable in the open end of the hole in the support structure, The shank of the tool element has at least one helical recess for forwarding particulate material out of the open end of the hole, and the drill bit is formed with cutouts at the cutting edges in the regions of the turns of the helical recess.</p> |
