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

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Rgrind angle 2β, by combining the equations shown on the lowerleft of Figs. A11 and bottom of A12. One obtains the resultlisted here as Eqn. 6.βR cos (β)O = 2R[1-cos(β)]O22β = 2 arc cosine [(d-WD)/2R] Eqn. 6Figure A12 Relation of overlap, Oto angle β and radius R of wheels.Because there is a small but significant difference in the wheel diameters for each of thevarious grit wheels, the calculation has to be made for each type of wheel.<strong>Experiments</strong> were done whichsystematically varied the overlap of thewheels and then measured the actual 2βangles achieved on grinding, and comparedthis to the predictions of the equation. Theinitial study was done on the T edges ofstainless blades shown in Fig. 5. The pregroundedges were reground with the 220grit wheel using 5 passes per blade. Theblades were then sectioned on a watercooled cut-off wheel and 2 sections from the center portion of each blade were mountedin standard metallographic plastic mounts and polished through 6 micron diamond.Digital images were then taken of the sections and these were examined with a graphicalsoftware program to determine the α and β angles shown on Fig. A13. <strong>Experiments</strong> weredone at 5 different overlap settings varying from roughly positions 1 to 5 on the controlwheel of the machine. The average value of the α angle was found to range from 16.6 to17.1 degrees, and the average value of the β half angle was found to vary with the overlapas shown on Fig. A14. At first glance the abrupt drop of the measured β angle below thetheoretical value that occurs at around 18 degrees is puzzling. Remember, however, thatthe measured α angle of these blades is around 17 o , which is probably just a bit smallerthan the pre-ground α angle on the blades. When one sets the β angle below the originalα angle, one wheel is then grinding along the entire length of the original α face of theblade. This will greatly reduce the rate at which the tip angle will change, and it isreasonable to expect that with only 5grinding passes the tip angle would fallbelow the theoretical value becausethere was not enough grinding done tochange the angle to the theoreticalvalue. These results show aninteresting practical point, which isperhaps obvious after more carefulconsideration. If one is simply tryingto re-sharpen the T edge of one ofthese stainless blades the overlapshould be set to have β either matchthe original α angle or to be justslightly larger than this angle.Overlap, (O) in mm10864222.5°53.1°Figure A13 Measurements made on T edges (Fig. 5) of stainless steel blades.220 grit WheelsTheoretical curveMeasured values05 10 15 20 25 30Half angle Beta (degrees)Figure A14 Comparison of calculated and measured values of β angle on T edges of SS blad54
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.
Page 1 and 2:
Experiments on Kni
Page 4 and 5: as a guide to good sharpening techn
Page 6 and 7: machine ground. The final 2β edge
Page 8: [2] Experiments wi
Page 11 and 12: Even on freshly dressed wheels a 2
Page 13 and 14: ledges of material has broken out o
Page 15 and 16: at the 2β edge angles of 50 and 70
Page 17 and 18: 7 All of the blades that were studi
Page 19 and 20: Japanese waterstones plus leather s
Page 21 and 22: Figs. 23-24. The blade of Fig. 25 w
Page 23 and 24: Figs 23 to 26. It appears that the
Page 25 and 26: [5] Experiments wi
Page 27 and 28: the 2β target hone angle set to ar
Page 29 and 30: lade of Fig. 33 along part of the l
Page 31 and 32: 3 Dropping the 2β edge angle from
Page 33 and 34: the 600 grit wheels were largely re
Page 35 and 36: seen that the buffing action is rem
Page 37 and 38: [7] Experiments on
Page 39 and 40: found that the softer steel produce
Page 41 and 42: optimum EW values found for afinal
Page 43 and 44: [9] Summary and ConclusionsThese ex
Page 45 and 46: 6 When the 2β edge angle is reduce
Page 47 and 48: Appendix 1Edge angle measurements w
Page 49 and 50: β = arc cosine((R 2 +L 2 -Y 2 -h 2
Page 51 and 52: YY = 45.5 mmLThese parameters can b
Page 53: Appendix 3The Tru Hone Sharpening M
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Experiments on Knife Sharpening John D. Verhoeven ... - BushcraftUK

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