| 摘要 |
To make holes with an undercut, the drills (1) used have a drilling head (6) with lateral cutting edges (7, 8) projecting laterally from the stem and are provided on the drilling stem, at a distance from the drilling head, with a thickened portion (10) serving as a swivel bearing and, approximately at the same distance from the thickened portion, with a collar-shaped depth stop (2). …<??>In order to prevent the drill from jamming in the wall when drilling downwards and when drilling relatively long holes, the drilling stem has at least one step (12), in the form of a cylindrical section of reduced diameter, which constitutes a sharp-edged transition and adjoins the thickened portion (10) in the direction of the depth stop (2). …<IMAGE>… |
