edge pro apex different angles?

[benchmade530]

I have a edge pro apex and when i sharpen my knifes, the bevel on one side is always different. It looks like the angle changes but i dont change it until i change stones but i use a stop collar to change angle depending on stone size.

ive sharpened benchmades, spydercos, kershaws, and a ontario rat 2 and the rat 2 is the only knife that has a even bevel

 

[fvdk]

Unlike most guided sharpening systems, The the pivot point is not fixed on the EP Apex but rotates around the upright arm so when you swing the arm left, the pivot point will be behind the upright arm while if you swing the arm right, the pivot point will be in front of the upright arm. I consider This is the reason why you have to keep moving the blade and limit the side-to-side movement of the arm to the width of the table.

See this post from Langrangian which describes it very well including many illustrations:
http://www.bladeforums.com/forums/s...Guided-Rod-Sharpeners?p=13104518#post13104518

I had an original EP but did not like it so I sold it again. I later bough the cheap Chinese Ruixin copy and I think it is better build to begin with, especially the large suction cup base makes it a lot more stable and a few tweaks make it even better. I have replaced the standard pivot arm with a ball joint rod end and added a drill stop collar for easy stone thickness adjustment. I also glued a Neodymium magnet under the table which holds the knife in place.

Frans

 

[cbwx34]

Unlike most guided sharpening systems, The the pivot point is not fixed on the EP Apex but rotates around the upright arm so when you swing the arm left, the pivot point will be behind the upright arm while if you swing the arm right, the pivot point will be in front of the upright arm. I consider This is the reason why you have to keep moving the blade and limit the side-to-side movement of the arm to the width of the table.

See this post from Langrangian which describes it very well including many illustrations:
http://www.bladeforums.com/forums/s...Guided-Rod-Sharpeners?p=13104518#post13104518

I didn't notice it before, but if I read that post right, he says he "exaggerated" the offset (beyond the side of the blade table width if the diagram is correct), to demonstrate the effect? If so, it would seem in the actual setup, the effect would be negligible.

I have a edge pro apex and when i sharpen my knifes, the bevel on one side is always different. It looks like the angle changes but i dont change it until i change stones but i use a stop collar to change angle depending on stone size.

ive sharpened benchmades, spydercos, kershaws, and a ontario rat 2 and the rat 2 is the only knife that has a even bevel

I'm not sure that what fvdk posted is the issue. Most production knives have a bias to begin with, but if you're seeing it on almost every knife you sharpen, I would slow down and carefully check that your duplicating what you do as you switch sides... it's easy to change what you're doing, since for half the sharpening you're using your non-dominant hand to hold the knife or work the stone rod. One side usually feels 'more comfortable' if that makes sense. You might try starting opposite of what you're used to, for example if you hold the knife with your left hand and the stone arm with your right to start... try reversing that when you start. It's also easy to over sharpen one side (the side you're comfortable with), so make sure you're doing equal work on both sides. After a bit of practice, this should go away.

You might also mark both sides with a Sharpie as you switch sides (especially in the learning phase) to insure things are consistent.

 

[Obsessed with Edges]

I have a edge pro apex and when i sharpen my knifes, the bevel on one side is always different. It looks like the angle changes but i dont change it until i change stones but i use a stop collar to change angle depending on stone size.

ive sharpened benchmades, spydercos, kershaws, and a ontario rat 2 and the rat 2 is the only knife that has a even bevel

Varying or mismatched bevel widths are almost always due to asymmetry in the blade's primary grind, relative to the centerline of the spine. In essence, it's because the steel on one side of the centerline will be somewhat thicker than on the other side, either overall or in portions of the blade. When sharpened, the thicker side will reveal a wider bevel as compared to the bevel width seen on the thinner side of the blade, with both sides sharpened at exactly the same angle. It's very, very common; blades with perfect symmetry relative to the centerline, and therefore equally thick on each side, are rare. That's why you've seen only one knife come out evenly (your RAT 2), among the examples you've mentioned. I wouldn't worry too much about the smaller error on part of the guided sharpener, if there's even any significant sharpener error at all; instead, the blade's own primary grind is making the bigger difference about 99% of the time. There'll also be differences and asymmetry in the profiles ground into each side (hollow grinds, sabre grinds, swedges, etc), which will affect how the blade lays against the 'table' on the EP, or how it rests against the clamp in other guided sharpeners. All of that will impact the actual angle at which the blade gets sharpened on each side, and therefore will impact bevel width as well.

BTW, you can almost always see some of the factory's grind asymmetry by looking straight-on at the tip of most knives, under magnification. The 'shoulder' of a bevel on one side will usually be higher/lower than on the other, or the edges of sabre or hollow grinds will be offset from side-to-side. I seldom see any blade that looks perfectly symmetrical, side-to-side, when viewed this way. And it's more obvious and even hideously unbalanced when seen on larger, thicker blades.


David

 

[Officer's Match]

Varying bevel widths are almost always due to asymmetry in the blade's primary grind, relative to the centerline of the spine. In essence, it's because the steel on one side of the centerline will be somewhat thicker (either overall, or in portions of the blade) than on the other side. The thicker side will reveal wider bevels at exactly the same angle, than is seen on the thinner side of the blade. It's very, very common; blades with perfect symmetry relative to the centerline, and therefore equally thick on each side, are rare. That's why you've seen only one knife come out evenly (your RAT 2), among the examples you've mentioned. I wouldn't worry too much about smaller error on part of the guided sharpener, as the blade's own primary grind is making the bigger difference about 99% of the time.


David

I believe this ^^^ has more to do with the asymmetrical bevel width than the moving/rotating angle guide on the EP, and could likely be remedied by working the "smaller" bevel side until it catches up with the "larger" bevel - if the removal of said steel is of less value to you than the asymmetry. I would likely be inclined to true it up so the apex was centered.

 

[fvdk]

I didn't notice it before, but if I read that post right, he says he "exaggerated" the offset (beyond the side of the blade table width if the diagram is correct), to demonstrate the effect? If so, it would seem in the actual setup, the effect would be negligible.

I'm not sure that what fvdk posted is the issue.

I am not sure if it is causing the issue but I just mentioned it as a possible cause.

I noticed it a long time ago when I had the original EP. Here are three arbitrary sample calculations where side a is the distance of the center of the pivot point to the edge of the knife.

At the center of the table

With the arm swinging to the left (pivot point moves 5mm behind the upright pivot arm)

With the arm swinging to the right (pivot point moves 5mm in front of the upright pivot arm)

It is not a huge effect but in this example, when not moving the blade, the difference from left to right is nearly 0.7 degrees so on one side of the blade the angle from tip to heel would be 12,2 to 12.88 degrees while on the other side of the blade, it would be reversed so 12.88 degrees at the tip and 12.2 at the heel.

 

[benchmade530]

Varying or mismatched bevel widths are almost always due to asymmetry in the blade's primary grind, relative to the centerline of the spine. In essence, it's because the steel on one side of the centerline will be somewhat thicker than on the other side, either overall or in portions of the blade. When sharpened, the thicker side will reveal a wider bevel as compared to the bevel width seen on the thinner side of the blade, with both sides sharpened at exactly the same angle. It's very, very common; blades with perfect symmetry relative to the centerline, and therefore equally thick on each side, are rare. That's why you've seen only one knife come out evenly (your RAT 2), among the examples you've mentioned. I wouldn't worry too much about the smaller error on part of the guided sharpener, if there's even any significant sharpener error at all; instead, the blade's own primary grind is making the bigger difference about 99% of the time. There'll also be differences and asymmetry in the profiles ground into each side (hollow grinds, sabre grinds, swedges, etc), which will affect how the blade lays against the 'table' on the EP, or how it rests against the clamp in other guided sharpeners. All of that will impact the actual angle at which the blade gets sharpened on each side, and therefore will impact bevel width as well.

BTW, you can almost always see some of the factory's grind asymmetry by looking straight-on at the tip of most knives, under magnification. The 'shoulder' of a bevel on one side will usually be higher/lower than on the other, or the edges of sabre or hollow grinds will be offset from side-to-side. I seldom see any blade that looks perfectly symmetrical, side-to-side, when viewed this way. And it's more obvious and even hideously unbalanced when seen on larger, thicker blades.


David

Is there a way to fix this?

 

[Obsessed with Edges]

Is there a way to fix this?

Not really. Since the blade's own grind creates most of the problem, only a complete and perfectly symmetrical regrind of the entire blade will fix that, which isn't realistic most of the time. And the issue is essentially only cosmetic anyway. Just focus on making the bevels on each side as flat and complete as possible, to a fully crisp intersection at the apex. If not using a guided system, some of the asymmetry in bevel width can be minimized by making a small change in the sharpening angle on one side or the other, to make the bevels look more even. With the guided system, unless you're willing to use a different angle setting on each side to compensate, you'll probably continue to see some asymmetry in the bevels. With asymmetrically-ground blades, there's a trade-off between even bevel widths or a symmetrically-ground apex angle: either alter the sharpening angle on one side to make the bevels appear more even from side-to-side, which will result in an uncentered and asymmetric apex angle; or accept the asymmetry in the bevel widths, in favor of an apex angle which is more centered, and will likely make the bigger difference in cutting performance. I'd generally opt for the latter, keeping the apex centered. An uncentered and asymmetric apex angle tends to 'steer' a cut in the direction to which the apex is biased, which is AWAY FROM the side sharpened at the more obtuse angle, and TOWARD the side with the more acute angle. Some knives are deliberately made and sharpened that way, for specific types of cutting (some Japanese knives for Sushi, etc); but most knives aren't.


David

 

[cbwx34]

Not really. Since the blade's own grind creates most of the problem, only a complete and perfectly symmetrical regrind of the entire blade will fix that, which isn't realistic most of the time. And the issue is essentially only cosmetic anyway. Just focus on making the bevels on each side as flat and complete as possible, to a fully crisp intersection at the apex. If not using a guided system, some of the asymmetry in bevel width can be minimized by making a small change in the sharpening angle on one side or the other, to make the bevels look more even. With the guided system, unless you're willing to use a different angle setting on each side to compensate, you'll probably continue to see some asymmetry in the bevels. With asymmetrically-ground blades, there's a trade-off between even bevel widths or a symmetrically-ground apex angle: either alter the sharpening angle on one side to make the bevels appear more even from side-to-side, which will result in an uncentered and asymmetric apex angle; or accept the asymmetry in the bevel widths, in favor of an apex angle which is more centered, and will likely make the bigger difference in cutting performance. I'd generally opt for the latter, keeping the apex centered. An uncentered and asymmetric apex angle tends to 'steer' a cut in the direction to which the apex is biased, which is AWAY FROM the side sharpened at the more obtuse angle, and TOWARD the side with the more acute angle. Some knives are deliberately made and sharpened that way, for specific types of cutting (some Japanese knives for Sushi, etc); but most knives aren't.

David

I'm not sure entire blades are consistently ground uneven.... I believe, it's more often that the final sharpened edge is put on that way. And I wouldn't recommend sharpening each side at different angles... that'll just accentuate the issue.

Is there a way to fix this?

The easiest way in my experience, is when you sharpen, spend a bit extra on the side with the smaller bevel, until the bevel's even out. You don't need to do it all at once... even with 'uneven' bevels, you'll still have a sharp knife.

It is not a huge effect but in this example, when not moving the blade, the difference from left to right is nearly 0.7 degrees so on one side of the blade the angle from tip to heel would be 12,2 to 12.88 degrees while on the other side of the blade, it would be reversed so 12.88 degrees at the tip and 12.2 at the heel.

I'll take your word for it... but in the end, I don't see it as a big issue.

 

[fvdk]

I'll take your word for it... but in the end, I don't see it as a big issue.

You are right, it is not a big issue and no issue at all if you use the EP like Ben shows in the instruction videos.
I guess I just think that it would be better system if they would implement a few improvements like I did with the Ruixin but as always, that is just my personal opinion.

 

[Obsessed with Edges]

I'm not sure entire blades are consistently ground uneven.... I believe, it's more often that the final sharpened edge is put on that way. And I wouldn't recommend sharpening each side at different angles... that'll just accentuate the issue.(...)

I've yet to see a blade that didn't have some asymmetry to the primary grind; it's the inconsistency of hand-grinding/finishing at the factory that likely leaves it asymmetric. Most of the time, it's negligible and probably missed in a casual look at the blade. But the differences can be noticed in a closer look, either in cross-section viewed from the tip, or they'll rear their ugly head when more extensive grinding is done, such as in thinning a blade by grinding/sanding flush on both sides, which almost always shows irregularities in blade flatness (warping, bending, divots or waves made by grinding belts, etc). Since almost all factory blades are at least partially shaped and/or finished by hand, it's almost inevitable there'll be some asymmetry.


David

 

[cbwx34]

I've yet to see a blade that didn't have some asymmetry to the primary grind; it's the inconsistency of hand-grinding/finishing at the factory that likely leaves it asymmetric. Most of the time, it's negligible and probably missed in a casual look at the blade. But the differences can be noticed in a closer look, either in cross-section viewed from the tip, or they'll rear their ugly head when more extensive grinding is done, such as in thinning a blade by grinding/sanding flush on both sides, which almost always shows irregularities in blade flatness (warping, bending, divots or waves made by grinding belts, etc). Since almost all factory blades are at least partially shaped and/or finished by hand, it's almost inevitable there'll be some asymmetry.


David

Ok... now you make it sound like the final edge is uneven (which I agree and said in my first response), whereas before, you said, "only a regrind of the entire blade" was the fix (don't agree with that). Maybe define how you're using 'primary grind' in this case?

 

[Obsessed with Edges]

Ok... now you make it sound like the final edge is uneven (which I agree and said in my first response), whereas before, you said, "only a regrind of the entire blade" was the fix (don't agree with that). Maybe define how you're using 'primary grind' in this case?

The primary grind, as I'm referring to it, is basically the whole grind from the spine down, before the secondary (edge grind) is applied. The secondary factory grind may or may not also be asymmetrical in itself, either in bevel widths being different side-to-side, or in the apex angle being more obtuse/acute on one side vs. the other. It's applied by hand on most factory knives, so I'd fully expect some asymmetry there as well. But, if the primary grind starts out asymmetric, that's the bigger roadblock to overcome in fixing it, if it can be truly 'fixed' to create BOTH evenly-wide bevels on both sides AND a symmetrically-centered edge. With an asymmetric primary grind, which is the literal foundation for the secondary, the 'fix' of the secondary grind will have to be one or the other (make bevels look even OR make the edge angle symmetrical; but not both), or some sort of 'in-between' compromise between the two, leaving some minor asymmetry in both bevel width and in edge angles on each side, but still minimizing the obvious appearance of it. To make the secondary symmetrical in BOTH bevel width and edge symmetry/centering relative to the spine's centerline, the primary 'foundation' grind would have to be corrected first (hence the complete regrind).


David

 

[cbwx34]

The primary grind, as I'm referring to it, is basically the whole grind from the spine down, before the secondary (edge grind) is applied. The secondary factory grind may or may not also be asymmetrical in itself, either in bevel widths being different side-to-side, or in apex angle being more obtuse/acute on one side vs. the other. But, if the primary grind starts out asymmetric, that's the bigger roadblock to overcome in fixing it, if it can be truly 'fixed' to create BOTH evenly-wide bevels on both sides AND a symmetrically-centered edge. With an asymmetric primary grind, which is the literal foundation for the secondary, the 'fix' of the secondary grind will have to be one or the other (make bevels look even OR make the edge angle symmetric; but not both), or some sort of 'in-between' compromise between the two, leaving some minor asymmetry in both bevel width and in edge angles on each side, but still minimizing the obvious appearance of it.


David

Ok,,, thanks. My interpretation of what you said earlier, that you can see the asymmetrical grind of the knife by looking at the tip under magnification, is because the edge is ground unevenly... not the entire blade. And it's fixable by fixing the edge grind how I stated earlier.. not the entire knife.

 

[Obsessed with Edges]

Ok,,, thanks. My interpretation of what you said earlier, that you can see the asymmetrical grind of the knife by looking at the tip under magnification, is because the edge is ground unevenly... not the entire blade. And it's fixable by fixing the edge grind how I stated earlier.. not the entire knife.

I think we're on the same page. With regard to looking at the grind's cross-section from the tip-on perspective, it's not just asymmetry in the edge (secondary) grind that shows up; sometimes (often, actually) other differences ABOVE the edge grind can be seen as well, such as the upper edges/shoulders of the primary's hollow or sabre-grind, on blades having such grinds. Sometimes you'll see the shoulders of those grinds being offset side-to-side, with one being higher/lower on the blade than is seen on the opposite side.


David

 

[cbwx34]

I think we're on the same page. With regard to looking at the grind's cross-section from the tip-on perspective, it's not just asymmetry in the edge (secondary) grind that shows up; sometimes (often, actually) other differences ABOVE the edge grind can be seen as well, such as the upper edges/shoulders of the primary's hollow or sabre-grind, on blades having such grinds. Sometimes you'll see the shoulders of those grinds being offset side-to-side, with one being higher/lower on the blade than is seen on the opposite side.


David

Haha... I'm not so sure... I was actually going to say if knives were that far off... you'd see it in other places, (pretty much where you mentioned). I spent the last ½ hour or so looking at production knives even using calipers... and just not seeing it, even though most came with uneven bevels that I corrected (using the technique I described before).

I know edge grinds (at least the sharpening) is often done by hand, but are primary (knife) grinds on production knives also hand ground? I kinda figured they were machine ground.

 

[Sticky]

I had the same problem....I came to the conclusion that FVDK did above that its because the pivot "orbits" the off center upright & doesn't remain dead center of the table as it swings and makes the distance from the pivot to the corners of the table longer or shorter depending which way it is going. In other words a major design flaw on an otherwise good overall idea. I made a semi clone at work out of aluminum and stainless where the rear upright was dead center, and a gimbal pivot was mounted dead center on top. The clone simply works better with a pivot that never goes off center regardless which way it moves. It eliminated the differing bevel widths right compared to left. It may be a small problem to some, but it was enough that my bevels looked weird to the eye so I sold my Edge Pro as I believe that's the entire purpose of guided systems is perfectly symmetrical bevels. I mostly free hand now anyways so it's back to basics here as I got tired of all the fuss. My freehand bevels are plenty "pretty" now and my cutting edges are as sharp as anything I have ever had with machines.
The rod end pictured above would accomplish the same thing if it was mounted directly in the center line of the table.

Anyways, I still need to put a linear bearing in that white nylon block for the rod to fit snugly and provide maximum smoothness, but this is the idea:

I'd like to build one similar to the edge pal with a Gimbal pivot, or a rod end, that traveled laterally along a LM guide rail on linear bearings. This would allow the precise same angle along a very long blade from heel to tip. I probably still wouldn't use the thing but I do like making machines!