a new way to calculate knife jig set up

[Jan]

Ken, you are asking a good question. The input parameters for the program (stone diameter and projection length) should be defined accurately.

Based on my calculations:
1.0   mm error in projection length estimation can change the desired bevel angle by 0.5°.
1.0   mm error in stone diameter estimation can change the bevel angle by 0.3°.
1.0   mm error in US height setup can change the bevel angle by 0.7°.

Hence be accurate, because if you are lucky, one error can compensate for the other, but if you are not lucky, the errors can sum.   

Jan

[wootz]

My estimate is in line with Jan's, and since the US height is set with 0.1mm accuracy, we know that the best achievable real life edge angle accuracy is within +/- 0.1 degree .

Of those three, for getting the utmost edge sharpness the wheel diameter and the Universal Support height are important; the jig projection is not, obviously, as long as you keep it the same through the sharpening session.

We measure wheels diameter with a 30cm caliper;
set the Universal Support height with a caliper depth probe;
and the jig projection length with the "jig setting block" described earlier.

In sharpening under 100 BESS, submicron edge apex, randomicity rules - you do exactly the same sharpening routine that gave you 40 BESS on the same steel yesterday, but get 70 today, a slightly different temper etc, all tiny inaccuracies factor in.

[Jan]

I have prepared a drawing showing the geometry of the unique Dutchman approach for grinding angle adjustment. Previously we have discussed here the fact, that Dutchman concept is approximate which guaranties bevel angle setting with an accuracy better than cca 1.0°. This is sufficient for majority of applications.

For those who need more accurate angle setting I have offered my Excel script which works without approximations.  https://forum.tormek.com/index.php?topic=2654.msg14297#msg14297

In this thread we are discussing Wootz's Grinding Angle Setter program which calculates the USB height for the desired grinding angle. Wootz uses the approximate Dutchman concept and transforms his stone – USB distance to USB height above the top of the Tormek housing.

The accuracy of the calculated USB height is limited by the accuracy of the Dutchman concept. In the second picture you can see that an inaccuracy in the USB height estimation may be almost 0.9 mm which will cause an inaccuracy of some 0.6° in grinding angle setting.

Jan

[wootz]

Jan, the way you assume about my applet accuracy is like me telling you that your Excel calculator can't be correct because inspired by Dutchman.
My concept and formulas aren't Dutchman's, how may you compare them if I've never published formulas from my applet in the public domain?
The idea was inspired by Dutchman's genius, but my software is different.

You might be judging by my initial script published on this forum, but as I wrote to you the other day, that script had inaccuracies and is a forgotten history - the applet is different. I told you that because of the inaccuracies I removed the script from that old post to prevent further confusion, yet you are bringing it up here again.

[Jan]

OK, Wootz, it was not a difficult forensic task. 
Because I do not have your applet I have asked forum members to provide me  with USB height for T7 with stone diameter 250 mm, projection length 139 mm and bevel angle 15°. I have got the USB height 169.31mm.

This number is biased by 0.87 mm as shown in my picture_02.jpg above. Because I assume that your segment of the applet, which is simple Pythagorean triangle, works correctly, I have deduced that the inaccuracy roots in the applet segment inspired by Dutchman approach. Even numerically the bias can be derived from the original Dutchman's formula.

You can verify your bias by grinding this angle on a blade. You will see that you will not get 15° (or 30°) angle. Let us know the results. 

Jan

[wootz]

Jan, the "bias" you are talking about is the bias only to your vision of how the cosine rule should be applied to the Tormek setup. Funnily enough, when I thought over your Excel formulas over a year ago, I initially thought the same, but you aren't doing transposition right.

[Jan]

Wootz, it is really funny! Please, if you can, prepare some explanatory drawing. 

Jan

[wootz]

Jan, I can only guess what your motivation was to take this discussion from our private dialogue to public, but I believe I've been patient enough not to hurt your self-esteem.
I'd suggest to return to private discussion, if you really want to know where you mistake.

[cbwx34]

When you guys get it hashed out... please share!  (It'll probably make my head hurt... but still find it interesting).

[Jan]

Wootz, the only reason why I posted the discussion here, on the Tormek forum, was your laconic refusal to discuss the issue with me privately via email.

As you know from my email, my intention was to draw your attention to a sketch and formula publically available on your website, where I saw some problems. You refused my suggestion with the argument, that documents on your website are not instructional, just a showcase.

I agree with your suggestion to return to private discussion.

Jan

[Jan]

When you guys get it hashed out... please share!  (It'll probably make my head hurt... but still find it interesting).

CB, thanks for your interest and also for to usage of the appropriate US verb's "to hash out".

Jan

[Ken S]

As a forum member, I value the many contributions each of you has made to this forum, and hope you will continue to do so.

As forum moderator, I can foresee more unfortunate downside risk than benefit to continuing this discussion on the forum. Therefore, I ask both of you as friends and gentlemen of good character to continue this discussion privately.

Ken

[Jan]

OK, Ken.

Jan

[Herman Trivilino]

The user inputs the grinding wheel diameter in millimeters and fractions of a millimeter. Next the angle is input in degrees and fractions of a degree. The program displays the distance between the universal support and the top of the Tormek.

What about the projection from where the knife jig's adjustable stop rests on the support bar to the bevel edge of the knife? It seems one would also have to input that distance?

[cbwx34]

The user inputs the grinding wheel diameter in millimeters and fractions of a millimeter. Next the angle is input in degrees and fractions of a degree. The program displays the distance between the universal support and the top of the Tormek.

What about the projection from where the knife jig's adjustable stop rests on the support bar to the bevel edge of the knife? It seems one would also have to input that distance?

Yes... that is entered also...