The study and forensic significance of drill bit use indicators.

A case study involving an improvised pipe bomb with a drilled fuse hole is presented. This case study and its accompanying research details drill bit use and/or nonuse indicators. These indicators are then further classified to develop relevant conclusion criteria. These criteria are: (1) trace deposits in the form of particulate and/or smears on the drill bit, especially inside the flute and the tip area, (2) physical damage including chipping, abrasion, and fissuring on the drill bit which mostly occurred on the flute edge bevels and lip edges, and (3) thermal damage. One or any combination of these indicators could be used as effective criteria for concluding drill bit usage. This study also determined that a drill bit produces well-defined toolmarks on swarf shavings that could be identified back to that particular tool, and there is no mechanical break-in period for obtaining reproducible toolmarks on newly manufactured or unused bits.