| 摘要 |
<p>The tool undercuts previously drilled hole in a masonry wall, utilising a screw-jack to pivot two cutting blades between axial and radially extended alignments. An externally milled nut is rotated by hand to operate the screw jack, being mounted on an externally threaded sleeve which is in turn mounted on the tool shaft. The blades may pivot about diametrically opposed axles positioned tangentially on the shaft, and may pivot and cross to gain the radial position, or may pivot in opposite directions. A sleeve with terminal ball bearing supports may connect the nut to a collar, the collar being coupled to the blades at points offset relative to the axles.</p> |
