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

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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.
Appendix 3The Tru Hone Sharpening MachineThe second machine used to sharpen blades inthis study was the Tru Hone machine manufactured bythe Tru Hone Corp. in Ocala FL. Figure A10 presentsa picture of the machine with a special bladeholderattachment made in the Mechanical Engineering shopat Iowa State University to fit the top of the machine.The machine employs 2 sets of interpenetrating wheelslocated at the front of Fig. A10. Figure A11 presents afront view of the 4 wheels at the left and a top view atthe right. As shown at the left the wheels rotate intothe knife edge. There is a plastic cover over the wheelsthat has been removed to clearly show the wheels inFig. A10. The cover contains a trough that allows thewheels to run wet if desired. Four aluminum oxidewheels, 100, 220, 400 and 600 grit were all used dry.A ceramic 1000 grit wheel of slightly reduced diameterrot.2 βrot.Washer DiameterWDRβOverlap, OdOdO = 2R -(d-WD)Top view of the 4 grinding wheelsFigure A11 Geometrical relationship between wheel overlap, O, and the tip angle 2β.was run wet in a water solution supplied by Tru Hone for use with this wheel.Performance was improved by the use of the liquid. Machine adjustments allow variationof the rotation speed and the distance between the wheels. Four of the 3.8 inch long SSblades could be held in the holder and sharpened in the same operation. The holder has avertical adjustment at the far end which ensures horizontal alignment of the holder bar,measured with a level at the top center of the bar.Figure A11 at the left shows that the 2β angle ground onto the blade edge dependson the amount of the overlap, O, between the wheels. A brass clamping washer is used onthe outer side of the grinding wheels. It is possible to measure the washer diameters,WD, and the distance between these washers, d, accurately with a digital caliper. Thediameter of the grinding wheels, 2R, may also be measure accurately with a digitalcaliper. Knowing these dimensions one can then calculate a theoretical value for the53
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: YY = 45.5 mmLThese parameters can b
Page 55: To overcome this problem withgrindi

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

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