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

employed for the initial grind on the ceramic wheel. It is a good idea to mark the bladeface oriented toward the knob on the initial ceramic wheel grind to avoid problems here.Effect of curvature of grinding wheel on the grind angle, βAs discussed above the hollow ground effectproduced by a circular grinding wheel will cause adecrease in the edge angle below the average grindangle, which is being called β in this appendix. Thiseffect can be explained with the aid of Fig. A8. If theblade in this sketch were ground on a flat stone theground surface of the blade would lie along the dashedhorizontal line as shown in the figure. The angle at theground edge would be given as β. It is apparent that thecurvature of a grinding wheel, shown here with a radiusof D/2, would cause the edge angle to be decreased bythe amount of ∆β shown on the figure. One can see fromthe diagram, that as the blade thickness T becomessmaller the value of ∆β becomes smaller, but as thediameter of the grinding wheel becomes smaller the value of ∆β becomes larger. It is arelatively simple geometry problem to show that ∆β is related to the blade thickness, T,and grinding wheel diameter, D, as,∆β = arcsine [T/(D x sin(β))] Eqn 5The predictions of this equation are shown in Fig. A9 for the 10 inch Tormek ceramicwheels on blades having thicknesses of T = 1/8, 1/4 and 1/2 inches.It is seen that the values of ∆β become fairly significant for common grindingconditions used on chisels, with β angles of 20 to 40 degrees and blade thicknesses of 1/8to 1/4 inch. However, if such chisels are finish-honed on a flat stone, as is commonlydone with hollow ground chisels [1,3], the edge angle is returned to the value of β.In the knife sharpeningexperiments done here with the Tormekmachine the final β angle was ground onblades with a previous α grind. Thevalues of α are shown in Figs. 5 and 6.Hence the β grind extended back from theedge only a very small distance and theeffective thickness of the blade contactingthe wheel at this point was never morethan 0.1 mm. Under these conditions thevalue of ∆β was less than 0.1 degrees, anegligible amount.52Reduction in edge angle, ∆β108642∆βΤβWheel ofdiam. = D/2Ground face usinga flat stone.∆βD/2Figure A8 Reduction of edge angle β due tocurvature of the grinding wheel.T = 1/8 inchT = 1/4 inchT = 1/2 inch05 10 15 20 25 30 35 40Edge angle, βFigure A9 Reduction in edge angle due to wheel curvaturefor a 10 inch wheel. T = blade (chisel) thickness.