Deep-bore drilling in metal working begins with a bore-hole depth of approximately 3x the tool diameter, extending in some cases up to 250x. The challenge of this method is to minimize wandering of the drill head center from the set axis, though due to its length the drill shaft no longer has sufficient flexural rigidity. Therefore so-called gun drills are frequently used for deep-bore drilling. These are designed so that they cut by removing material, yielding a minimal shearing force and causing the drill to guide itself along the wall of a pre-drilled hole. Consequently, the drilling dust itself absorbs the lateral forces when drilling. This makes a pilot bore-hole or jig bushing necessary at the start of the drilling process. Over the past several years, double-edged, over-length helical drills have been used increasingly as deep bore-hole tools. The ratio of length to diameter here, in contrast with gun-deep-bore drilling tools, is limited to about 40. The advantage of this tool type versus a gun-deep drill is in the increase of tooling speed by multiples.
Sources: En.wikipedia.org, Internet, own documentation (Werder limited compagny) Back
