Fixed angle knife sharpeners

[washington1963]

I would like your perspective on fixed blade rod sharpeners. I appreciated the lansky i used for years. But geometry got the best of me on its function. Considering that the blade lays on a plane to the perpendicular 90 degee vertical post that holds the rod and stone. The selected angle and stone and rod become effectively the hypotenuse. All angles of a triangle total 180. With the 90 degree being fixed. As the stone slides down a longer blade the triangle pivots on the same axis as the rod and stone. As the stone reaches, the blade angle by geometry must be ever more acute of an angle, while the rod end must become less acute for the rod to slide out to allow the stone to reach further. The height of the vertical stayes the same. The length of the lower side lengthens as the triangle pivots. The knife sharpening angle is more acute at the blade tip than at the point of the blade clamp. Can anyone verify or explain if this is an incorrect perspective. Thank you

 

[777 Edge]

You need to visualize looking at this triangle from the side, not from the top angle perspective of sharpening. Visualize the pitch of a roof, with a string tied to the top center. Now imagine moving that string along the gutter from one side to the other and along the pitch of the roof. The pitch doesn't change.

If the knife was a straight blade, then the angle won't change from heel, to center, to tip. If the tip is curved up or belly curved down a lot, then the angle between those points do change.

What is worth noting with a Lansky system, is that the angle guide is marked for a certain width of blade, and only protruding a set length out of the clamp. If the blade is very wide (not long, but wide), then the angle will be lower. Secondly, a Lansky clamp (when used on a full flat ground blade, like a Spyderco or typical kitchen knife grind) if clamped on such a blade grind, then the angle marks are also not correct due to the fact that both sides of the clamp will be angled to follow the grind of the full flat blade. This makes a Lansky type clamp excellent for clamping versatility, but worth considering that the angle won't be exactly as read on the guide marks.