| 摘要 |
The present invention relates to hole cutting in general and, in particular to the cutting of holes (34) and the like in plasterboard, plywood, plaster walls and the like. The use of rotary drill tools such as hand-drills, mains or battery powered machine drills is ubiquitous in the building trade whether for maintenance or original build, by carpenter, electrician, gas-engineer or plumber. Equally most homes have a number of drill-drivers for Do-lt-Yourself (DIY) projects hobbies or otherwise. Typically, a DIY drill-driver for home will be provided with a set of drill bits which are cutting tools used to create cylindrical holes (34), almost always of circular cross-section. Drill bits come in many sizes and have many uses. A hole saw (14, 20), also known as a hole cutter, is a saw blade having an annular (ring) shape, whose annular kerf creates a hole in the work-piece without having to cut up the core material. It is used in a drill. Hole saws typically have a pilot drill bit (11) at their centre to keep the hole saw (14, 20) centralised, to prevent the saw teeth (18) from moving from the intended place of cutting or "from walking", as is commonly said. A problem exists, on the one hand that it is difficult and/or clumsy and/ or time consuming to change a hole saw (14, 20) bit. On the other hand especially in the case of the enlargement of holes (34), a pre- existing hole may prevent placement of a central twist-drill bit (11). |
