- Joined
- Jan 28, 2002
- Messages
- 790
I was unsatisfied with the EZE-Sharp documentation on edge angle settings, so I did my own calculations 
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Definitions
Variables
Measurements
Assumptions
Example: Quick & Dirty Calculation
Example: Thin Stone
Example: Thick Stone (i.e. coarse waterstone)
Example: Wide Blade (i.e. cleaver)
Conclusion
.Definitions
- Guide Rod = Rod attached to the stone holder.
- Crossbar = Rod in the T-bar.
- Witness Lines = Slightly raised lines on the surface of cast metal parts. These generally indicate where the two (or more) halves of the mold came together.
- Vertical Plane = Plane formed by the T-bar assembly, specifically by the witness line that bisects the T-bar.
- Horizontal Plane = Plane formed by the flipover witness line. The flipover holds the blade in the horizontal plane.
Variables
- h = T-bar height setting, read directly from it. Note that this is marked in cm, but my calculations are in inches.
- w = Distance from the blade edge to the flipover edge.
- t = Overhang of the stone on the stone holder.
- θ = Half of the total edge angle.
Measurements
- Vertical plane to flipover edge is approx. 8-5/16" (8.3125").
- Top of crossbar is approx. 1/4" (0.25") below horizontal plane when h = 0.
- Rods are 0.314" in diameter.
- Stone holder is 0.494" tall.
Assumptions
- Angle dial set to 0°.
- The Bladesharpener is manufactured according to specs. That is, lines that are supposed to be straight really are, perpendicular elements are 90° to each other, etc. For example, the guide rod should screw exactly in the middle of the stone holder.
- The guide rod touches the crossbar at the vertical plane. This is not exactly true, since the crossbar is a rod (circular cross-section) the actual point of contact is slightly left of the vertical plane. However because the crossbar diameter is small and θ is usually <20°, I left this out of the calculation.
- The stone overhang (t) may be set to a constant value by using spacers when securing the stone holder on the stone. Put the stone on a flat surface and a spacer at each end. Tighten the holder as the ends rest on the spacers.
Example: Quick & Dirty Calculation
tan θ = h/8.3125
If I want θ = 15°, set h to 2.23" or 5.7cm.
If I want θ = 15°, set h to 2.23" or 5.7cm.
Example: Thin Stone
Let t = 1/8" and w = 1/2"
If I want θ = 15°, h should be 2.33" or 5.9cm.
Not too far from the quick & dirty results. If I had set h = 5.7cm, θ would have actually been 14.4°.
If I want θ = 15°, h should be 2.33" or 5.9cm.
Not too far from the quick & dirty results. If I had set h = 5.7cm, θ would have actually been 14.4°.
Example: Thick Stone (i.e. coarse waterstone)
Let t = 1" and w = 1/2"
If I want θ = 15°, h should be 3.24" or 8.2cm.
Now we see a significant difference from the quick & dirty results. If I had set h = 5.7cm, θ would have actually been 8.9°!
If I want θ = 15°, h should be 3.24" or 8.2cm.
Now we see a significant difference from the quick & dirty results. If I had set h = 5.7cm, θ would have actually been 8.9°!
Example: Wide Blade (i.e. cleaver)
Let t = 1/8" and w = 1.5"
If I want θ = 15°, h should be 2.60" or 6.6cm.
Again, h is higher than expected from the quick & dirty results. If I had set h = 5.7cm, θ would have actually been 13°.
If I want θ = 15°, h should be 2.60" or 6.6cm.
Again, h is higher than expected from the quick & dirty results. If I had set h = 5.7cm, θ would have actually been 13°.
Conclusion
The real advantage of a sharpening jig like the EZESharp is being able to reproduce angles precisely on every stroke and with different hones, but knowing the actual angles is useful for all sorts of things. The stone overhang (t) and clamping distance (w) can influence the final edge angle significantly. Of course, these results apply only to straight edges parallel with the flipover edge. Calculations for curved edges would be much more difficult and need to be done on a case-by-case basis. I also didn't examine adjusting the angle dial to other than 0°, which might be necessary if you want obtuse edges.
Yeh the instruction manual is crap.