Lansky and galco sharpeners

[washington1963]

Im trying to understand that with geometry of a 90 angle triangle, the blade flat, to the verticle upright holding the rod. You get a exact angle directly to the blade. But on a knife blade with any length the semetry of the triangle pivots on the vertical axes of the rod holder maintaining the one angle of 90 degrees.. Still a 90 on the plane of blade to rod holder, but as the stone streches further the length of the bottom leg of the triangle has to lengthen to reach the tip of the blade. As in geometry, that change in length has to cause a more acute angle on the angle meeting the stone, and a more obtuse angle at the rod to vertical stanchion in correlation to the 90 dregee vertical and the two corresponding angles remaining to total 180 degrees. You can not change the lengths of a side with out effecting the angles. Is this correct? Seems to be principles of gemoetry.

 

[Stuart Davenport Knives]

Indeed you are correct. With those type of fixed angle sharpeners, the angle will be slightly different towards the tip. Alex on YT (Outdoors55 I think is the channel) has a good video explaining it that I saw not too long ago.

 

[Stacy E. Apelt - Bladesmith]

You are correct. The edge angle decreases as the base of the triangle lengthens. The issue is somewhat moot for two reasons. One, the decrease is small. Two, the tip's lower angle cuts better this way. It does not get as much wear and damage as the middle of the blade does, so the more acute edge holds up fine.

 

[dfarm]

You can mitigate it somewhat on most blades by kind of averaging out the edge. I take a straight edge and go between the tip and the plunge grind, then put the clamp jaws parallel to the straight line, in the middle of the length.