Preliminary statement : geometry and I (me ?), we said good-bye to each other a long time ago. The only thing I remember is that a right angle boils at 90? ... <img src="/images/graemlins/grin.gif" alt="" />

And now, you want me to understand geometry in english !!! Argh...... <img src="/images/graemlins/crazy.gif" alt="" />

I don't even know what's the 'included' angle ... Should I guess it's the angle made by the two sides (slopes ?) of the cutting edge ? <img src="/images/graemlins/confused.gif" alt="" /> (*)

So, I just took the Lansky sharpener and make a few measurements.
Let's say the tool make a right triangle ABC, with the right angle being point C.
When my RSK is positionned in the tool, the very edge of the blade (point A) is at 11cm from C.
The 30? hole (point B) for the stone's guide is at (about) 5cm from point C.
A bit of trigonometry (told you it was a long time ago : I had to look in an encyclopedia to get this right ... well, I hope it is .. <img src="/images/graemlins/blush.gif" alt="" /> ) :
hyp = about 12 cm
sin(a) = opp/hyp = 5/12 = 0.41666666
>>> a = about 27?
so the angle made by the two sides of the edge is about 54?

If the edge of the blade was positionned exactly at the end of the tool, hyp would be about 10cm >> angle would be exactly 30?

Therefore, the larger the blade, the smaller the angle, using the same hole as a guide.
So the angles indicated on the Lansky tool are just rough references, nothing more.
For instance, the lowest position marked 17? is only to be used on razor style blades. Does the RSK qualifies for such a style ?

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Did I compute/understand something wrong ? Any math geak around here ??

TIA for correcting me.


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(*) included angle = angle included between the two sides ! Is that it ? Did I finally got it ?