Identifying Handsaw Tooth Shape Based on the Micro- and Macroscopic Analysis of the Kerf Floor Contour

Abstract

Skeletal trauma analysis is a major facet of forensic anthropology casework and can entail interpretation of sharp force saw trauma. Hand-powered saws are commonly used in cases of dismemberment and analysis requires differentiating class characteristics. Features of the kerf walls and floor provide information utilized in identifying set, shape, size, power, and direction of sawing motion of the tool. The focus of this study is to examine validity and reliability of determining tooth shape class characteristic (rip versus crosscut) from features of the kerf floor. Two crosscut and three rip handsaws, ranging from 6 to 16 teeth per inch, were used to make 30 incomplete cuts per saw for a total of 150 cuts. Each kerf floor was analyzed macroscopically and microscopically using a digital microscope at 30 × magnification by three observers of different experience levels (expert, experienced, and novice). Profile shapes were classified as U-shaped/concave (rip) or W-shaped/convex (crosscut) by each observer for all 150 cuts. Reliability tests using Cohen’s kappa ranged from substantial in the two less experienced observers to almost perfect in pairwise comparisons with the expert. Microscopic classification accuracy was 94.0% (423/450) for all three observers and macroscopic examination increased accuracy to 99.8% (449/450). Saw wear and tooth size were not a significant determiner in correct identification of saw tooth type. Overall, tooth shape can be reliably and accurately determined from incomplete cuts.