Uneven bevels

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Feb 1, 2007
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So I put my Grayman Dua on my edge pro last night. It was the first time I'd sharpened it so I wanted to regrind the levels to a more usable angle. I set the sharpening rod at 22 degrees and got to work with the factory 120 grit stone. The factory was pretty uneven and took me awhile to raise a consistent burr but when I flipped the blade over to work on the other side, no matter how hard I tried I couldn't get the bevels to match width. What am I doing wrong? I held the blade in the same position relative to the sharpening table on both sides and never changed angles so why is one side bevel wider than the other?




Not the best pictures but you can clearly tell one bevel is wider than the other. All advice is welcome. Thanks for your help
 
One side of the knife could be thicker than the other. The primary grind, not the bevel.

Did you grind one side completely then switch?

It's always best to grind a little on each side until a burr forms. Grinding one side completely down before switching to the other side can have many bad results. To me, it looks like your edge is asymmeteric from grinding one side too much.

You will want to inspect the centering of the edge bevel with the full thickness of the blade at the heel. The edge apex should be the centerline of the knife.

6635E6BB-6420-4FEC-A2E1-1A22304A738B.jpg

Next, you will check the centering of the tip by looking down at the edge. This will give you a good idea of bevel symmetry. In this picture the edge is facing the camera like the last picture.

85802E81-B94B-4628-B1ED-57371EEB019C.jpg
 
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To me the edge looks pretty centered. I tried to flip periodically so I didn't grind too much on one side. Although, the side with the wider bevel took considerably longer to reach the apex than the other side. When I put it on the sharpmaker before this one side hit the whole edge but the other side was only hitting the shoulder. Is it possible the edge was just off center out of the box?

I'm not too worried about since this is a hard user and it's still shaving sharp, just the aesthetics bother me.

How would I go about fixing this?
 
Until you know the cause, the fix is difficult to prescribe.

I am not sure what your definition of "hard user" is, but I am not sure a slightly uneven bevel warrants much concern if you are going to be really stressing the edge in use....the differences in performance are pretty slight compared to the forces a lot of "hard users" exert.
 
It's purely aesthetic for me, it just bothers my OCD. I can't even put it in my pocket without thinking about it, lol!

I measured the edge This morning and it's pretty centered. Its literally, about the width of 2 hairs, biased towards the side with the skinnier bevel.

Its just the looks that bother me, it cuts like a laser.
 
Looks like the primary grind on the presentation side is shallower (lower angle). Measure down from the spine to start of primary grind on both side and compare. If one side is shorter, then that side is shallower and will display sharpening results you have illustrated, other things being equal (example: you have not ground one side of secondary more than the other - secondary is centered with cutting edge).

If primary or secondary bevels are not even, you'll get what you see when sharpening on fixed angle system. Also, this can happen if you "accidentally" sharpen one side with flat on table and other with primary on table :-/

Edit: I always inspect & test grind each side of a fresh knife to understand how each side of the knife matches up, and then make a "plan" for how that knife will be sharpened. Knives that have uneven primary bevels always need special consideration. My primary daily carry (which has dead even primary bevels), I am currently asymmetrical (differing left/right) secondaries because I like the way the combination feathers wood and slightly steeped side gives a little added strength to cutting edge, while still allowing low approach angle of the left side when right-hand cutting. "Even" bevels (in my mind) are purely aesthetics, not really performance related.
 
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Can you measure using calipers from the knife edge at a reference point to the spine edge on one side and compare that to the measurement from the same reference point to the spine edge on the other side opposite from the first measurement? This will tell you if the knife edge is centered on the spine, at least. If the distances are not equal, then this would help explain why your bevels are not equal, assuming symmetrical blade design.

You should be able to continue grinding down at the same angle on the side where the bevel is short until the bevels are even. The bevels will get even as you keep grinding metal off the edge until the bevels equal the same measurement. Of course, if the edge was centered to begin with with the bevels uneven, then the edge will be off centered from the spine's centerline but your bevels will be even.

Isn't OCD a pain? I understand. I have both OCD and ADD; things have to be perfect but they can't stay that way for too long.
 
You cannot measure from the spine to the bevel, that's just not how it works.
 
Some knives are just made off center. Happens during the manufacturing process. When you use a sharpening device that is consistent then this shows up. Not too common.
 
Your not doing anything wrong.

Nearly every Ontario knife I own has come this way. (and I own more than 10)
 
The primary bevels were not ground the same on both sides which will move the apex when its sharpened on a fixed angle system.
 
Jason B. said:
You cannot measure from the spine to the bevel, that's just not how it works.
Click to expand...

Feel free to correct what I'm thinking. I wasn't saying to measure from the spine to the bevel. If you look at the knife point on and imagine a cross-section of the blade, the corner points of the spine on top and the edge point of knife on the bottom describe a triangle. If you compare the distances of the spine corners to the knife edge and they're equal, that's an equilateral triangle and says the knife edge is centered between the spine thickness.
 
The reason that logic does not work is because the edge is centered on the full thickness of the steel which has been ground on either side creating an A and B side that are often different in grind geometry. The perfect grinds we all hope for are just that, a hope and a dream. The blade height might be okay but the grind thickness per side is the important factor.

When you sharpen you are sharpening to the centerline of the blade, if the blade grinds are lopsided or wavy this effects the bevel on the side with the distorted grind. In the case of the saber grind, if one side starts it grind .005 higher than the other and overgrinds the centerline of the blade by .001 then one of the two edge bevels will always be larger than the other because the blade is misground.
 
That was what I was driving at in my original post. If the edge was along the centerline between the spine edges and the bevels are uneven, then the blade isn't symmetrical to the centerline or has "uneven grinds" in your words. If the knife edge isn't along the centerline, it would help explain the uneven bevels assuming symmetrical blade design.

In the case of asymmetrical grinds, you can make the bevels equal but the edge would be off the centerline which is what the last sentence in my second paragraph states.

So we're not in disagreement.

Rey HRH said:
This will tell you if the knife edge is centered on the spine, at least. If the distances are not equal, then this would help explain why your bevels are not equal, assuming symmetrical blade design.

You should be able to continue grinding down at the same angle on the side where the bevel is short until the bevels are even. The bevels will get even as you keep grinding metal off the edge until the bevels equal the same measurement. Of course, if the edge was centered to begin with with the bevels uneven, then the edge will be off centered from the spine's centerline but your bevels will be even.
Click to expand...
 
Let's see if a 2-minute schematic helps or hurts:

Uneven%2BBevels.png


The left image has symmetrical primary and secondary (edge) grinds.
The center-left primary grind is symmetrical but the edge-bevel has been ground more on the left than the right, resulting in an uneven bevel-width at the edge and off-center apex - easy fix, just grind the right-side until they are even.
The center-right primary grind is uneven - the right primary was ground deeper than the left-side, resulting in uneven edge-bevel as well as uneven height of the flats. To fix this, grind the left primary bevel until it matches the right side.
The right image primary grind is uneven - the right primary was ground at a steeper angle than the left-side, resulting in uneven edge-bevel. To fix this, grind the left primary bevel until it matches the right side.

Does this help or hurt?
 
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chiral.grolim said:
Let's see if a 2-minute schematic helps or hurts:


Does this help or hurt?
Click to expand...

drawings are always good especially in this case. Actually, it's best but I'm not a drawings guy, I tend to be more about words. Although, you take it another step and point out how to fix the problem which is acceptable. With me, I would just take my choice between a centered edge or even bevels as fixing the primary grind would be a lot more work. Besides, it's not known yet whether the OP's knife does indeed have any uneven primary grinds. My first post was just to help the OP figure out what, if any, in the knife's geometry is driving his uneven bevels issue.
 
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With consideration that the primary bevels are not even ... or if the primary goal is to have even looking secondaries ...,

Maybe ..., if the goal is simply to have symmetric looking secondary bevels on both sides of the knife, then perhaps a simple solution like grinding/sharpening the secondary bevels with the primary bevel laid flat on the table of the EdgePro (would negate the effects of the primary bevels being uneven with respect to having even looking secondary bevels). Test or set the angle of the EP to the side you like (with primary flat on the table) then flip to the other side. User would need to consider they would be taking material off the smaller looking bevel, until such time both sides matched. This "option" is one of the things that the EP design allows a user to do (where other fixed blade systems only allow grinding based on the flats and the secondaries widths are then relative to the primaries). Net result, the secondary bevels will appear even and be relative to the center-line as the primary is. The actual angle of the secondary bevel (relative to the center-line) will be slightly different, but visually what most people will see will look symmetric or "even".

Question is; do you want bevels that are even, or bevels that look even ...?

EDIT: chiral.grolim, Great Diagrams (as usual). If what I referenced makes sense, perhaps can you diagram/illustrate as my explanations are most likely more confusing that they could be ...?
 


Let me take a cue from Chiral and use a drawing I got off the Internet.

Assume the cross-sectional blade design is symmetrical and the basic cross-sectional shape of the blade fits within the triangle with the important points being the two bottom corners of the triangle correlate to the two corners of the spine and the point on top being the edge of the knife. I didn't bother or don't have the ability to put in the bevels from the sharpening that would be in the area around the top.

If the same sharpening angle was used on both sides of the triangle and the same amount of material was taken off, then the length of the resulting bevels would be equal to each other. But that's not the case with the OP, he says he has uneven bevels.

If he measures and compares the distances from the edge to either corner of the bevel and find that the distances are not the same, then it means he hasn't taken enough material from the side with the shorter bevel. If he takes the advice I said of "grinding down at the same angle on the side where the bevel is short until the bevels are even," then the edge will be at the centerline and the angles will be congruent with the angles in the picture.

But if he finds in his initial measurement that the distances are equal meaning the edge is along the centerline but have uneven bevels, then this is the result of sharpening to the centerline of the blade as Jason pointed out but having different thicknesses on either side of the centerline -- a non-symmetric cross section. You can still make the bevels even as I also said but the edge will now be away from the spine's centerline.

If I just further confused the issue for the OP then I apologize.
 
Rey HRH said:


Let me take a cue from Chiral and use a drawing I got off the Internet.

Assume the cross-sectional blade design is symmetrical and the basic cross-sectional shape of the blade fits within the triangle with the important points being the two bottom corners of the triangle correlate to the two corners of the spine and the point on top being the edge of the knife. I didn't bother or don't have the ability to put in the bevels from the sharpening that would be in the area around the top.

If the same sharpening angle was used on both sides of the triangle and the same amount of material was taken off, then the length of the resulting bevels would be equal to each other. But that's not the case with the OP, he says he has uneven bevels.

If he measures and compares the distances from the edge to either corner of the bevel and find that the distances are not the same, then it means he hasn't taken enough material from the side with the shorter bevel. If he takes the advice I said of "grinding down at the same angle on the side where the bevel is short until the bevels are even," then the edge will be at the centerline and the angles will be congruent with the angles in the picture.

But if he finds in his initial measurement that the distances are equal meaning the edge is along the centerline but have uneven bevels, then this is the result of sharpening to the centerline of the blade as Jason pointed out but having different thicknesses on either side of the centerline -- a non-symmetric cross section. You can still make the bevels even as I also said but the edge will now be away from the spine's centerline.

If I just further confused the issue for the OP then I apologize.
Click to expand...

This is assuming the spine is ground 90 to the centerline. If not your theory
holds no water :)
 
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