Improving penetration twist drills
On a conventional twist drill (left), the web thickness is 15 to 20 percent of drill diameter. increases, the thrust forces required for drill penetration also increase.
USA - Drill for penetrating hard metals - Google Patents
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Description:This invention relates to bores, and more particularly to drills or penetrating devices used either for perforating or for recessing an extremely hard metal. As conducive to a clearer understanding of this invention, it may be well to point'out that conventional drills cut or chip their way through the work with the result that if the work is extremely hard, the cutting edge of the instrument quickly dulls and requires resharpening. If too much pressure happens to be applied to the tool, the drill breaks or twists out of shape and becomes useless. The conventional cutting drills, and even grinders, require a lubricant or an abrasive to facilitate their efflcient operation.