Boring Extra-Deep Holes

Figure 11-24. Using an extension bit to form an extra-deep hole.

Holes that are deeper than you can form by using a conventional bit can be bored with an extension bit (Figure 11-24), a special tool that in many cases is no more than a regular drill bit that has been brazed onto a rod. The procedure is to bore to the quill's maximum extension and then, after retracting the quill, to move either the table or the power plant so the drill will reach the bottom of the hole. Thus you can deepen the hole by again extending the quill. Since the rod part of the extension doesn't have flutes, you must retract frequently to clear waste chips from the hole.

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