| 摘要 |
The cup-shaped grinding wheel is supported by a spindle which can be inserted into a drill chuck, used as a driving unit. It carries a flanged plate (14) forming a drill guide. This plate has a ring of holes (19) if different sizes for a range of drill (22) diameters. Under the plate are two inner plates (15,16), the lower plate (16) having shaped openings (21) matching the drill shape. - The upper plate has stop lugs (17) projecting downwards towards the rim (29) of the grinding wheel. The lugs are of a metal which is harder than the material of the grinding wheel, and have sloping edges (17a,b) which match the sloping parts of the grinding wheel rim. The grinding wheel is resiliently supported.
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