| 摘要 |
An apparatus useful for forming in a curved surface, an enlarged hole surrounded by an upturned flange whose unattached edge lies substantially in a common plane, uses a drill rod, a set of bits, and a mechanism for forming an upturned flange. A first bit attached to the lower end of the rod forms an initial hole. A second bit, spaced axially along the rod, forms a widened oval hole with tapered sides upon continued axial and rotary movement of the rod relative to the workpiece. A flange forming mechanism is then extended beneath the edge region of the hole and pulled through the hole while rotating, to form the upturned flange. A third bit mounted peripherally with respect to the second bit is used to smooth and level the flange edge and to provide it with a desired shape.
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