Over time, many methods have been utilized for deep-hole drilling. Most of them, including drilling with solid or indexable-insert drills and interpolating with a center-cutting endmill, consume excessive machine power and waste material. A more cost-effective and accurate method is trepanning. During a trepanning operation, a hole is cut into a workpiece with a hollow rotary tool and a single center core, or slug, is removed. This differentiates trepanning from conventional drilling, where all the material removed is in the form of chips. Deep-hole drilling is defined as an operation having a depth-to-diameter ratio greater than 5:1. While the principles are the same, this article will focus on holes with depth-to-diameter ratios up to 3:1 and diameters to 12".
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