What causes uneven bevel width?

[KennyB]

This happens to me a lot. Ever conceivable way I have for measuring the angle tells me that I've kept the same edge angle, but I still wind up with uneven bevel width, and usually it's narrower at the tip.

Is it possible to just have not ground enough metal at the tip to have got the bevel the same width as the rest of the blade, even though the angle is the same?

Near the heel it looks MUCH wider and I know it's because I accidentally held the angle too low at one point, you can kind of see the curvature in it too. But that just makes me think that the bevel width isdependent on the angle so maybe the angle at the tip IS different? I've got angle wedges to check against, I know the trigonometry and I've got Fred Rowe's ERU to use as an angle gauge and they all say the angle is the same at the tip... So why the uneven bevel?

My theory is that I've just removed more metal from the flat portion of the blade near the heel because it's flat and I can keep most of that area in contact with the stone as I grind. When the belly and the curve starts, I have to work more to lift the pommel to follow the curvature of the blade, but this is a lot more cumbersome and not nearly as fast as it is at the heel so I tend to kind of stop when it's "good enough" even though the bevel widths are different.

It's no big deal but something that bothers me because sometimes it happens and sometimes it doesn't, and I just want to know if it's a matter of not putting in enough work--ie not evening it out all the way along the edge--or if the angle is off. But if it's the latter, it's certainly by no amount that I can verify so it doesn't seem significant. It occured to me that since it was at the belly and I have to lift the pommel maybe it was just a slight variation in angle, but I've sharpened other knives with large bellies and had no problem keeping the bevel even so... It just seems random whether this will happen or not, but I have noticed it happens more when I sharpen an Izula than other knives.

Could the fact that the blade stock itself ( i.e. thickness of the blade ) narrows as it nears the tip have something to do with it too? Since it's thicker at the heel, there's more metal to remove to get it to the specific angle than there is further up toward the tip. So it would make sense that the bevel formed would be "wider" at the heel since it had to transect more metal. But here's the problem with that... I see plenty of other Izula edges that are uniform bevel width all the way through, and plenty other knives with distal tapers that have even bevel width as well... So I'm not really sure that has anything to do with it.

P.S.
It's a 22 degree inclusive bevel with a 30 degree inclusive microbevel--looks like a burr thanks to my crappy camera.

Edit:
Added more pics 'cause the lighting makes it hard to notice what I'm talking about

 

[Obsessed with Edges]

Thickness of the steel at (or just immediately behind) the edge makes the biggest difference, assuming the angle is actually remaining constant (and that's difficult to do, especially freehand). At a given fixed angle, the bevels will be wider in thicker steel, and narrower in thinner steel. If the blade tapers from heel to tip (called a distal taper), the thinner steel at the tip will most influence the appearance (width) of the bevels there. Blades with less of a taper (in thickness) from heel to tip will sometimes show a WIDER bevel near the tip, because the cutting edge at the tip is closer to the thicker steel near the spine of the blade.

Factory bevels on many blades look nice & even in width (most of the time); but this only happens because they sharpen the tips at a wider (more obtuse) angle, more often than not.


David

 

[HeavyHanded]

From the pics it looks like you might be dropping the handle low off the edge of the stone or some similar mechanical defect. It really helps to keep the fingertips of the offhand exactly where you are grinding. I used to have a similar effect plague me when I become inattentive on the left side of the blade right at the ricasso. I ID'd this as being a poor contact zone for those offhand fingertips and mod'd my grip to accommodate better contact - problem solved.

If it only happens on one side of the blade, it is frequently a warp - thicker bevels on either side of a thinning region can indicate a concave warp. Convex warps on the opposite side can sometimes present as a thickening of the bevel but frequently do not present very obviously. The concave warp will always show itself to some degree and con only be eliminated by treating that exact region like a recurve to even the grind out.

 

[Rey HRH]

Here is my thought for you to consider: How are you checking your angles? Are you holding the angle relative to the blade surface or relative to the centerline plane of the blade? Physically, you can use the ricasso (a term I learned here) which is the flat thick part of the blade nearest the handle. I believe this would be the full thickness of the blade blank and would be parallel to the centerline plane of the blade.

I have no evidence or clue whether this is your problem, I'm just throwing another item to check off.

 

[KennyB]

From the pics it looks like you might be dropping the handle low off the edge of the stone or some similar mechanical defect. It really helps to keep the fingertips of the offhand exactly where you are grinding. I used to have a similar effect plague me when I become inattentive on the left side of the blade right at the ricasso. I ID'd this as being a poor contact zone for those offhand fingertips and mod'd my grip to accommodate better contact - problem solved.

If it only happens on one side of the blade, it is frequently a warp - thicker bevels on either side of a thinning region can indicate a concave warp. Convex warps on the opposite side can sometimes present as a thickening of the bevel but frequently do not present very obviously. The concave warp will always show itself to some degree and con only be eliminated by treating that exact region like a recurve to even the grind out.

I'm not sure what you mean in the first paragraph, do you mean the area of the bevel right in front of the ricasso where it the bevel shoulder very clearly has a bit of a "arch" effect? Because that particular spot was caused by holding the angle too low during the initial grinding phase. The second picture shows the other side (the "Izula" side versus the "Rowen" side) which I didn't mess up on.

I'm mostly talking about the effect at the tip, because I'm positive ( well a least as much as one can be freehanding ) that I held the angle at a constant there.

I think I've observed what you're talking about in your second paragraph in kitchen knives that have been flexed and kind of bent.

Rey,

I use a couple of different methods. First using a caliper and calculator I measure the thickness of the blade at the bevel shoulder, and then the width of each bevel, and find the angle with the proper trigonometry (I will spare the details) and then also check that by measuring the distance from the center-line of the blade to the surface of the hone, and the width ( from spine to edge ) of the blade--those dimensions form a triangle and one can check the angle on that.

Then I also have an "ERU" (Edge Renewal Utility) that Fred Rowe makes. A bit hard to describe, but imagine something a bit like a protractor that had jaws which you could open and shut like pacman open and closes his mouth. Using that tool as an angle gauge I can find the angle by holding it and the knife up to light and seeing if the surfaces are flush with the surfaces of the blade with no light escaping--very much like using a machinists' square if you've had experience with that. Then finally after getting that angle, I put some sharpie on the bevel and actually use the ERU and see if it takes all the sharpie off to confirm that angle exists along the entire portion of the blade. Since I freehand there's inevitably a bit of marker left, but as long as there is a clear and uniform band of new steel visible emanating from the edge, I know that portion of visible steel is dead on to the angle.

Oh and recently I had someone cut me a set of angle wedges with their skill saw--or some kind of saw with an angle measure on it heh. In any case, using the wedges I can carefully check the angle at each portion of the blade which removes much "waver" from my hand, and using short strokes as to eliminate any more wavering I just do the same kind of marker trick to make sure I'm hitting the angle right.

Then I usually grumble that I wish I could afford a laser goniometer from CARTA and resolve that I probably got it close enough

 

[Rey HRH]

Rey,


Oh and recently I had someone cut me a set of angle wedges with their skill saw--or some kind of saw with an angle measure on it heh. In any case, using the wedges I can carefully check the angle at each portion of the blade which removes much "waver" from my hand, and using short strokes as to eliminate any more wavering I just do the same kind of marker trick to make sure I'm hitting the angle right.

Re-reading my post, I can see why you answered the way you did. I wasn't asking how you determine the bevel angle. I do that myself. I have Fred's ERU also although I haven't used it yet but that's how I plan to use it. I do use angle blocks I got from Fred to set my wrist for the angle.

My question has to do with how you're checking / setting the angle prior to doing your sharpening stroke. The portion of your post that I quoted makes me think to continue to pursue this question with you. You said, "using the wedges I can carefully check the angle at each portion of the blade." So, how do you use the wedge to check at each portion of the blade? I came to the conclusion which Fred also stated at another thread that the wedge has to be used against the ricasso portion. When I was using the wedge for the tip and curve portions, I had to set the wedge near the far edge and hold the knife's ricasso against the wedge which meant the rest of the blade was past the stone edge and extended below the stone.

If you use the wedge against the grind (which I think is the naturally easy but incorrect way), then the resulting angle is not relative to the blade's centerline but instead to the grind angle. Imagining the typical blade geometry in my head, I'm thinking the thinness of the blade near the tip will result in a larger angle to the horizontal using the wedge and a smaller angle when the wedge is used against the grind nearer the hilt. If I am correct in my imagination (and not just wanting to be "right"), then this is aligned with your observation that the bevel is wider near the heel and narrower at the tip.

Since you're familiar with the trigonometry and how to measure angles, maybe you can think about it some more, look at how you're using the wedge, and the resulting angles as you use the wedge for each blade portion and see if I'm close or not. Good luck.

 

[KennyB]

Here is my thought for you to consider: How are you checking your angles? Are you holding the angle relative to the blade surface or relative to the centerline plane of the blade? Physically, you can use the ricasso (a term I learned here) which is the flat thick part of the blade nearest the handle. I believe this would be the full thickness of the blade blank and would be parallel to the centerline plane of the blade.

I have no evidence or clue whether this is your problem, I'm just throwing another item to check off.

Ohhh okay I see what you're saying. Well, when I said that I carefully checked along each portion of the blade what I mean is that instead of doing a whole stroke from heel to tip like I usually would, I use the wedge to get the angle, then pick the blade up, and rub just which portion I wanted to check. This way I can be sure I'm not wavering and causing any false positives or false negatives and can be more sure that the part where the marker is rubbed away is where I was making contact.

I don't think that would be the problem in this case though. As you said if you held the blade surface against the surface, then the angle would be relative to the blade grind's angle instead of the centerline of the knife. But the thing is, as long as the blade angle is the same throughout, so will the angle that you grind it. It won't be the angle of the wedge you used, but it will stay constant.



I got mine before he was doing the metal angle wedges. Been considering buying one just for those

 

[chiral.grolim]

Thickness of the steel at (or just immediately behind) the edge makes the biggest difference, assuming the angle is actually remaining constant (and that's difficult to do, especially freehand). At a given fixed angle, the bevels will be wider in thicker steel, and narrower in thinner steel. If the blade tapers from heel to tip (called a distal taper), the thinner steel at the tip will most influence the appearance (width) of the bevels there. Blades with less of a taper (in thickness) from heel to tip will sometimes show a WIDER bevel near the tip, because the cutting edge at the tip is closer to the thicker steel near the spine of the blade.

Factory bevels on many blades look nice & even in width (most of the time); but this only happens because they sharpen the tips at a wider (more obtuse) angle, more often than not.


David

^This is the primary cause of "uneven" or tapering bevel-width while maintaining a consistent angle. :thumbup:

The second most common cause is using a clamp-system like the Lansky or DMT aligner or Wicked-Edge, but that doesn't apply here.

 

[Fanglekai]

Something to note is that few knives if any are perfectly symmetrical. If you use a guided system it will reveal that asymmetry. To counter it you can sharpen at different angles on each side to maintain the bevel width. Additionally the blade might not be even down it's full length, that is to say the tip is usually a higher angle the the rest of the blade. You would have to sharpen at a higher angle to compensate for this.

Personally I just sharpen and go on about my day as uneven bevels don't bother me. I think for most knives it would be rather difficult or at least time consuming to try to keep even bevels if it sees regular use.