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Drill bit: Difference between revisions
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Traditional twist drill bits may tend to wander when started on an unprepared surface. Once a bit wanders off-course it is difficult to bring it back on center. A center drill bit provides a good starting point as it is short and therefore has a reduced tendency to wander when drilling is started. | Traditional twist drill bits may tend to wander when started on an unprepared surface. Once a bit wanders off-course it is difficult to bring it back on center. A center drill bit provides a good starting point as it is short and therefore has a reduced tendency to wander when drilling is started. | ||
While the above is common, it is incorrect practice. Centre drills are meant to create a centre for lathe work only. The correct tool to start a hole is a | While the above is common, it is incorrect practice. Centre drills are meant to create a centre for lathe work only. The correct tool to start a hole is a spotting drill, because the included angle of the spotting drill is the same as a conventional drill bit so the drill bit will then start without chatter. Centre drills wander as easily as anything else in hand-held power drills - for such operations, a [[centre punch]] should be used to spot the planned hole centre prior to drilling a [[pilot hole]]. That said, a centre drill works nearly as well as a spotting drill for most rigidly-clamped drilling operations, especially in softer metals such as aluminium and its [[alloys]]. | ||
The small starting tip has a tendency to break, and it is economical and practical to make the drill bit double ended. | The small starting tip has a tendency to break, and it is economical and practical to make the drill bit double ended. | ||
