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Module 13: Toolmark Identification - Coggle Diagram
Module 13: Toolmark Identification
Operations
cutting
metal chip failures
continuous chips (long ribbons of metal)
typically found in machining a ductile metal with a sharp cutting tool, resulting in a fine surface
discontinuous chips (segmented chips)
break up into particles; associated with brittle metals and a coarser result on the surface of the workpiece
continuous chips with built-up edge
accumulate tiny particles that weld to the workpiece, producing coarse surfaces on the workpiece; this often occurs if the cutting tool begins dull
lathe operations
turning
rotates the exterior of a workpiece against a single-point cutting tool
facing
the cutting tool is used on the surfaces perpendicular to the rotating spindle
boring
a single-point cutting tool enlarges a hole beyond the capability of a drill or reamer and works the interior of a piece
milling
face milling
the surface of the workpiece is parallel to the cutter face located at the end of a spindle or shaft; the cutters are located on the face and edge of the rotating cutter
peripheral milling (slab)
the surface being machined is parallel to the (often helical) cutting teeth in the periphery of the tool
end milling
fluted cutting edges are arranged on the circumference and end of a rotating shaft that is vertical to the workpiece; the cutting teeth are found on the end of the cutter and the circumference of the cutter body
Toolmark Identification
incidental toolmarks
striated toolmarks
produced when a tool is placed against another object and moved parallel to and across the object with pressure applied
impressed toolmarks
produced when a tool is placed against another object and sufficient force is applied to the tool to leave an impression
reloading and handloading
cartridge case marks
holding tools on a reloading press which grips the base of cartridge cases
resizing tools which squeeze fired cases back to their original specifications
crimping tools used for some loads to press the mouth of cases slightly into a cannelure used as a crimping groove
bullets bearing bullet-seating toolmarks
pattern matching
the process of determining whether or not details of striated marks or impressions on two objects correspond
Tool Actions
scraping: a flat-bladed tool held at 90 to surface
pinching: an opposed blade cutting tool, such as a pair of bolt cutters or diagonal wire cutters
shearing: shear cutters, the blades of which are offset to pass by each other in the cutting process, such as tin snips or scissors
slicing: a single-bladed tool, such as a knife or axe
prying: a prying tool using leverage to force open a locked door or cover at one of its edges
gripping: a gripping tool with opposing jaws, such as a pipe wrench, pliers, or a vise
crimping: an opposing jawed tool designed to press material together without cutting it
AFTE Range of Conclusions
identification
"agreement of a combination of individual characteristics and all discernable class characteristics where the extent of agreement exceeds that which can occur in the comparison of toolmarks made by different tools and is consistent with the agreement demonstrated by toolmarks known to have been produced by the same tool"
inconclusive
some agreement of individual characteristics and all discerable class characteristics, but insufficient for identification
agreement of all discernable class characteristics without agreement or disagreement of individual characteristics due to an absence, insufficiency, or lack of reproducibility
agreement of all discernable class characteristics and disagreement of individual characteristics, but insufficient for an elimination
elimination
a significant disagreement of discernable class characteristics and/or individual characteristics
unsuitable for comparison
this outcome is appropriate for evidence items that do not bear microscopic marks of value for comparison purposes or are so small or fragmentary as to have no value