Tool Mark Identification


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Unformatted text preview: ors, tin snips, wire cutters, and pruning shears. © Precision Forensic Testing Tools – Slicing Action Slicing tools cut materials by moving a sharp blade along the direction in which it is traveling. These tools include knives and razors. © Precision Forensic Testing Individual Characteristics Within the class characteristics are the individual characteristics. These are microscopic imperfections on the edge of the cutting surface. They are caused by: The manufacturing process Use Abuse Rust © Precision Forensic Testing Individual Characteristics Because individual characteristics are unique on the surface of the tool, they are essentially fingerprints. These unique marks will be transferred on any object they come in contact with. Screwdriver blade tip at 20X magnification Lineman’s pliers blade at 20X © Precision Forensic Testing Tools – Manufacturing By understanding how tools are made, we can understand how the class and individual characteristics are made. Tools are typically made using a combination of machining methods. The initial shape of the tool may be stamped from a solid piece of metal. Another way to make the basic shape of tools is by forging. Forging involves shaping the metal into the desired shape under high pressure. This is typically done by a hammering action. Tools can have the final shape and cutting edge made by milling or grinding. © Precision Forensic Testing Stamping Some blades of tools are made from steel barstock. The barstock is fed into a hydraulic press that acts as a “cookie cutter” that stamps out the basic shape of the tool blade. © Precision Forensic Testing Grinding Grinding is a method used to...
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This note was uploaded on 04/09/2011 for the course CHEM 4461 taught by Professor Max during the Spring '08 term at Lamar University.

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