Tool Mark Identification

Theyare impressedandstriated

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Unformatted text preview: put an edge on a blade. A grinding wheel is composed of small stone fragments embedded in a matrix. The surface of the grinding wheel is always changing as it comes in contact with metal. This causes the marks it makes to be individual. © Precision Forensic Testing Grinding Surfaces that are ground typically have parallel marks The individual characteristics of a ground surface can be seen below. © Precision Forensic Testing Milling Milling machines remove metal using a rotating carbide cutter. Unlike a drill, mills can cut using the side or the end of the bit. © Precision Forensic Testing Milling The raw stamping of the blade is placed in a milling machine to cut the contour of the cutting blade into the stamping. This will commonly require two passes. The first pass cuts the basic shape of the blade. The next pass cuts the secondary cutting angle. © Precision Forensic Testing Milling The milling process leaves marks in the direction of the travel of the mill. In this example, the mill cut parallel to the edge. The individual characteristics can be seen in the picture below. © Precision Forensic Testing Toolmarks Two types of toolmarks that can be made when a tool comes in contact with an object. They are impressed and striated. These marks are reproducible and can be used for comparison and identification of a toolmark to a particular tool. © Precision Forensic Testing Toolmarks ­ Impressed Impressed Toolmark ­ The mark produced when a tool is placed against an object and enough pressure is applied to the tool so that it leaves an impression in the object. The class characteristics (shape) can suggest the type of tool used to produce the mark. The individual characteristics can be used to identify the tool with the mark. Also called Compressi...
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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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