Angle Dissmis

[Pietje]

Hello!
I had the problem, that adjusting the T8 to 15°, the knifes angle was different. Thats because the thick of the blade and the brideness of the blade make a dissmis of round about 1,4°.
So I made a formula for the TormekCalc Excel sheet in this way:

=WENNFEHLER((Z6-(ARCSIN(((J6/2)/I6)))*180/PI())/2;"")

Z6 is the angle I like to grind.
J6 is the thicknes of the blades back.
I6 is the brideness of the blade.

[tgbto]

Hallo Pietje,

I am not sure what you are referring to, but the angle in TormekCalc (and in Dutchman's tables for that matter) is the angle at the apex when the apex is centered and aligned with the center of the jig shaft.
So the thickness of the blade has no impact... other than the well-known issue with the SVM-45 not being self aligning.

There is also an issue when the wheels you go from a wheel with a smaller radius to a wheel with a larger one, and there are tools in the spreadsheet to help you optimize your time and still end up with the right angle.

[cbwx34]

Hello!
I had the problem, that adjusting the T8 to 15°, the knifes angle was different. Thats because the thick of the blade and the brideness of the blade make a dissmis of round about 1,4°.
So I made a formula for the TormekCalc Excel sheet in this way:

=WENNFEHLER((Z6-(ARCSIN(((J6/2)/I6)))*180/PI())/2;"")

Z6 is the angle I like to grind.
J6 is the thicknes of the blades back.
I6 is the brideness of the blade.

I would be interested to know how you measured to determine that there was a difference that needed correcting.  It looks to me that you're referencing off the blade taper from spine to edge?  (What is "brideness"?)  The sharpening angle is not based on this.

jvh has made a video that shows whether or not blade thickness matters:

[Pietje]

I was thinking in the way, you are thinking.
I use a laser goinometer but there is at no time the angle, I tried to gring.

[cbwx34]

I was thinking in the way, you are thinking.
I use a laser goinometer but there is at no time the angle, I tried to gring.

It would be hard to say without knowing more... but I wonder if the issue lies elsewhere, and your fix was just a coincidence.  For example, aren't most goniometers only accurate within a couple of degrees?

But, as long as you stay consistent, it probably won't matter with the end result, just more setup work.

[Pietje]

Hello!

I use a laser goinometer but there is at no time the angle, I tried to gring.
[/quote]
It would be hard to say without knowing more... but I wonder if the issue lies elsewhere, and your fix was just a coincidence.  For example, aren't most goniometers only accurate within a couple of degrees?
[/quote]
You are right.I dont know the tolerances of the goinometer.
Can this be the solution?

[Pietje]

  (What is "brideness"?)  The sharpening angle is not based on this.

[/quote]
ARCSIN. An angle function of Excel.

[tgbto]

Hi. In any case, if you take the arcsine of (J6/2)/I6, you already have the angle in dps (degrees per side), which is what TormekCalc uses, or half the total edge angle. So why would you again divide the result by 2 ?

And as we said before, and as explained in the video, as TormekCalc or Dutchman's formulas are based on projection distance, the (apex) angle you get is independant from blade thickness. However the beam of your laser goniometer has a nonzero radius, so the reading you get will essentially be scattered between the apex angle and whatever angle is measured as the edge of your beam hits the concave grind made by the wheel. The latter angle being higher than the apex angle. This is more likely to happen on a thick blade where concavity is discernible.

[Pietje]

Hi. In any case, if you take the arcsine of (J6/2)/I6, you already have the angle in dps (degrees per side), which is what TormekCalc uses, or half the total edge angle. So why would you again divide the result by 2 ?

I divided with 2 because in my TormekCalc V2.70 the raw is named cutting angle and not grinding angle.

[tgbto]

I'm not sure what you are referring to in the drawing, but Delta (as the greek letter) in TormekCalc is the bevel angle in degrees per side.

Z6 is the declared angle, so subtracting half the total blade angle makes sense (dividing I6 by 2 to get the half-thickness in the process), but why divide the difference again ? It looks to me like you're computing :

((Delta-(BladeAngle/2))/2)

[tgbto]

Something I missed when I first looked at your screencap.... To further comment on the meaning of the angle in TormekCalc, maybe it's not obvious in german, but in english it goes :
declared angle/measured angle/ground angle

• "declared" being the angle given by the manufacturer (e.g. 16dps for most shun knives)
• "measured" being what you read on a goniometer, or better, what you get from bevelCalc with the sharpie method and measuring the top-of-usb-to-wheel distance
• "ground" being whatever you decided to grind using - most likely - TormekCalc, based on either the angles above, or Wootz' advice, or your own reasons.

So, rare exceptions aside, you shouldn't have 20dps deklariert and 10dps geschliffen.