Experiments on Knife Sharpening John D. Verhoeven ... - BushcraftUK

To overcome this problem withgrinding rate dependent on the angle ofa pre-ground surface, experiments weredone in which an edge was ground onthe non-sharpened side of the stainlessblades, shown as the A edge of Fig. 1.These edges were ground with 100 gritwheels and around 150 passes wererequired to produce a fully groundedge. Four overlap values, O, wereused and the blades were sectioned,mounted and polished as above andOverlap (O) in mm210 12.5 15 17.5 20 22.5 25Half angle Beta (degrees)Figure A15 Comparison of calculated and measure β angles on A edgeof SS blades.average values of the tip angle were measured and are presented in Fig. A15. It wasfound that the measured and calculated angles deviated by roughly a constant amountover the entire range of measurements. The results show that the change in the calculatedangles with change in overlap is a close match to the measured data, but that the actual tipangle values appear to be consistently lower than the calculated values by around 0.8 to1.2 degrees. This final result shows that the measured tip angles agree with thecalculated values fairly closely. Hence, the equation for calculating the tip angle providesa good estimate, provided one grinds the blades adequately.In several of the experiments done with the Tru Hone machine the final 2β grindwas done with an angle slightly increased from the subsequent grind to insure that thefinal grind was restricted only to the final sharpened edge. This was always done whenusing the 1000 grit wheels for the final grind. Because the 1000 grit wheels have asignificantly smaller wheel diameter, and because the wheels had to be interchanged priorto this final treatment, the equation for calculating tip angle proved very helpful. Thedesired increase in tip angle was used to calculate the required distance between wheels,i.e., the d dimension. Examination of the ground tips in the SEM showed that setting theoverlap this way was very effective in providing a small increase in tip angle, so that onlythe tip region was ground in the final operation.76543Theoretical CurveMeasured dataFigure A16 presents the calculationfor the reduction in edge angle (Eqn. 5, page52) with the 3 inch diameter wheels used onthe Tru Hone machine. The T = 0.68 mmcurve should apply to the SS blades for the Aedges. Hence the edge angle in these bladesground to a 2β angle of 40 o would be reducedby around 3 o . The T = 0.1 mm curve gives themaximum reduction expected on grindingblades with a pre-existing α bevel, the Tedges. The values are expected to be only afraction of a degree.Reduction in edge angle, ∆β55321T = 0.68 mm (A edge SS blades)T = 0.1 mm (T edge SS blades)05 10 15 20 25 30 35 40Edge angle, βFigure A16 Reduction in edge angle due to wheel curvaturefor a 3 inch wheel.