Usually performed in a machining center where a specially adapted tool is pressed, during rotation, into an existing round hole to reshape it.
The face of the tool consists of a cutting edge that runs along the entire outer edge. The tool is conically shaped and angled in relation to the center line of the pre-drilled hole. Because of the way the tool base is mounted and rotates freely, a wobbling movement occurs which, while the tool is pressed into the hole, causes the cutters to cut one edge of the inner surface of the hole at a time and reshape it according to the cross-section of the tool.
