The logic behind whetstone angle guides?

[perky890]

Hi guys.

Im considering purchasing a whetstone to sharpen my global kitchen knives. The whetstones come with a clip on guide to help maintain a 15 degree sharpening angle.

Im a little confused as to the logic behind the guide. Im thinking, due to the fixed height of the guide, the closer the clip is to the edge of the blade, the steeper the angle will become, therefore it wont be a consistent 15 degree angle between knives.

For example, with the guide clipped to the spine of a deep bladed knife like a vegetable chopper, surely the blade angle will be shallower than with the guide clipped to a shallower depth knife like a pairing knife?

Is my logic correct or am i missing something?

Thanks

 

[TheOne45]

Correct.

 

[Cementite]

I think what's more important than whether you have 15° or 19.2° or 22.5° is consistency in the bevel angle, and that inconsistency in the bevel angle is the biggest difficulty that new freehand sharpeners run into, because when you make one stroke at 15° and the next stroke at 22.7° and the third stroke at 19.8° ... you end up with a convex bevel and a rounded edge...

For beginners, the clip-on guides (or the more complex and expensive jigs) can at least help eliminate some of this inconsistency, even if they don't give the exact bevel angle marked in degrees...

Welcome to the forum, BTW, from one newb to another.

 

[TheOne45]

.. you end up with a convex bevel and a rounded edge..

I never measured but always wondered how accurate can we hold/maintain the angle during free hand sharpening.
I would say more or less we all have somehow convex edges.

 

[Obsessed with Edges]

Yeah, the main thing about the guides is to provide consistency in whatever the set angle turns out to be. And that's perfectly fine. Rarely is it important to set or expect a specific number for the angle. Most any knife will perform very well at any angle within 15-20 degrees per side, and some edges even narrower than that, so long as whatever the number turns out to be, it's maintained consistently from one pass to the next, from start to finish. And as assumed, the further the knife edge is from the front of the clamp, the lower (more acute) the angle will be, regardless of how the clamp is marked for a given angle setting.

And when or if one begins to acquire a skill for freehand sharpening, the key there is to be able to feel when the apex is just making contact and then focus on not going higher than the held angle in that moment, which otherwise will widen the edge angle and round it off. I do this by holding the angle conservatively LOW to begin the sharpening pass on the stone. This means the bevel BEHIND the edge first makes contact. It'll feel kind of slick on the stone this way. Then, I very gradually turn the edge down into the stone during the sharpening pass, by raising the spine slightly. When the edge itself starts making contact, it'll BITE into the stone's grit and the difference will be felt in the fingers holding the blade. When I feel that, I STOP lifting the spine while finishing the sharpening pass. That keeps the convexing limited to the area BEHIND the edge, which is OK. The convexity that comes with freehand is fine and in some cases even advantageous for certain types of cutting. Just work to keep most of that convexity in the shoulders of the secondary bevel behind the edge, and not at the edge itself.