Edge Pro - somehting is wrong (scrathed edge)

Marblo · Mar 29, 2014

Hi,
Im having problem with polishing the edge. Im not sure If Im the problem or the stone.. I tried cleaning the stone and it also seems that it does not need to be flattened. The angle is also the same. I took a picture of the scratches. After couple of strokes they disappear and appear somewhere else. What could be wrong? :grumpy:

fervens · Mar 29, 2014

Did you adjust the edgepro for the new stone's thickness?
What are you using to wet the stones/clean them?
Do you adjust the knife's position on the platform when you do different areas of the blade?
Did you lap the stones previously?
Go back to the last grit and do the entire edge again. Then do just one pass with the next stone. Look to see where it ground the steel. Use a sharpie if needed.

Cynic2701 · Mar 29, 2014

In my experience those are the result of uneven pressure and angle. While the Edge Pro does help to control the angle, there is a small amount of "wobble" in the arm. The amount of pressure you use throughout your stroke can also change and cause these to occur.

Guided systems like the Edge Pro/Wicked Edge/KME/etc. are only accurate at the specific arc that you measure the angle (typically straight and parallel), but the angle changes as you swing the arm along the length of a knife--since the blade won't follow (unless you have a circular blade) the same arc of the arm, the angle becomes more acute the further you get from the "base" angle parallel to the device.

cbwx34 · Mar 30, 2014

Cynic2701 said:
Guided systems like the Edge Pro/Wicked Edge/KME/etc. are only accurate at the specific arc that you measure the angle (typically straight and parallel), but the angle changes as you swing the arm along the length of a knife--since the blade won't follow (unless you have a circular blade) the same arc of the arm, the angle becomes more acute the further you get from the "base" angle parallel to the device.

It seems like the angle would change as you move away from the pivot (basic geometry right?), but it turns out the angle doesn't change along the straight part of the blade, no matter how far out you go. I first saw this on a page on the Wicked Edge website. I had to see for myself, so I mounted a straight piece of aluminum in the WE, and with the aid of some dental floss and angle cube took some measurements...

It turns out if you look at the bottom photo, where I sighted the camera along the edge, the angle that is actually formed between the stone and the edge never changes (verified with the angle cube)...

A forum member, Lagrangian (also on this forum) provided a mathematical proof of this, which must be right since it made my head hurt.

As you can see in this diagram though...

(this is actually the same knife clamped at two different locations)

... the angle does change as soon as the stone starts tracking around the belly of a knife (and rather quickly depending on where it's clamped), which is why placement to follow the belly toward the tip is important.

Once I got this, it made figuring out how to place the knife on the WE or EP easier (don't have a KME but it would be the same), to have a consistent bevel from heel to tip.

Marblo · Mar 30, 2014

Fervens

1) yes

2) I used to use water + drop of soup but now Im running only on watter. 2.2) when Im done I clean in under flowing water. Between sharpening I use a lot of water + clean it with a rag then water it again

3) No, the knife stays at the same spot

4) Lap.. as flatten (Im from czech)? No.

5) I just did that and found out that those scrathes are there also from the 600 stone :-(

Ok, I think this could be my fault because sometimes the knife moves just a little bit. Do you guys have any idea how to make sure the knife does not move and always eds up in the same spot? With some knives it is no problem but for example this Rat-1 is quite difficult due to the blade geometry.

Marblo · Mar 30, 2014

Okay.
I was experimenting how to make it more accurate and this is what I devised. It could work - the blade is very stable and harder to move. Maybe I can find something better than cardboard.

fervens · Mar 30, 2014

Yes, lap as in flatten. Most of the questions were to make sure you weren't contaminating the stones. You may still have a slight convex to the edge causing you to hit spots randomly. Try magnets on the bottom to help stabilize the blade.

warlord260 · Mar 30, 2014

Marblo said:
Okay.
I was experimenting how to make it more accurate and this is what I devised. It could work - the blade is very stable and harder to move. Maybe I can find something better than cardboard.

You are on the right track. I would adjust the blade guide so the edge barely clears the table, and use the magnet. I made blade shims like your, but out of plastic drawer dividers.

Marblo · Mar 31, 2014

Im expecting angle cube any day, so I will wait till then. I was using my android phone which is not that accurate. So lets hope that those scratches were result of wrong angle and with this shims and angle cube they will be only past

Cynic2701 · Apr 2, 2014

cbwx34 said:
It seems like the angle would change as you move away from the pivot (basic geometry right?), but it turns out the angle doesn't change along the straight part of the blade, no matter how far out you go. I first saw this on a page on the Wicked Edge website. I had to see for myself, so I mounted a straight piece of aluminum in the WE, and with the aid of some dental floss and angle cube took some measurements...

It turns out if you look at the bottom photo, where I sighted the camera along the edge, the angle that is actually formed between the stone and the edge never changes (verified with the angle cube)...

A forum member, Lagrangian (also on this forum) provided a mathematical proof of this, which must be right since it made my head hurt.

As you can see in this diagram though...

(this is actually the same knife clamped at two different locations)

... the angle does change as soon as the stone starts tracking around the belly of a knife (and rather quickly depending on where it's clamped), which is why placement to follow the belly toward the tip is important.

Once I got this, it made figuring out how to place the knife on the WE or EP easier (don't have a KME but it would be the same), to have a consistent bevel from heel to tip.

Perhaps I wasn't clear in my post, but I am actually arguing precisely what Lagranian's diagrams show: that as a guided system follows the curve of the blade, the angle changes along the arc length of the blade. You would need to "swing" or pivot the blade with the curve in order to keep it the angles the same.

cbwx34 · Apr 2, 2014

Hmmmm.... well this is what you said before...

Cynic2701 said:
Guided systems like the Edge Pro/Wicked Edge/KME/etc. are only accurate at the specific arc that you measure the angle (typically straight and parallel), but the angle changes as you swing the arm along the length of a knife--since the blade won't follow (unless you have a circular blade) the same arc of the arm, the angle becomes more acute the further you get from the "base" angle parallel to the device.

... as opposed to now...

Cynic2701 said:
Perhaps I wasn't clear in my post, but I am actually arguing precisely what Lagranian's diagrams show: that as a guided system follows the curve of the blade, the angle changes along the arc length of the blade. You would need to "swing" or pivot the blade with the curve in order to keep it the angles the same.

... so now I'm not sure what you mean. Your first post seems to indicate the angle changes along the straight portion which it doesn't. Your second one seems to indicate it changes along the curved portion, which is only partially true... it may or may not depending on the position in relation to the pivot (which is what the last diagram in my earlier post indicates).

Cynic2701 · Apr 2, 2014

cbwx34 said:
Hmmmm.... well this is what you said before...

... as opposed to now...

... so now I'm not sure what you mean. Your first post seems to indicate the angle changes along the straight portion which it doesn't. Your second one seems to indicate it changes along the curved portion, which is only partially true... it may or may not depending on the position in relation to the pivot (which is what the last diagram in my earlier post indicates).

Yes, "the angle changes as you swing the arm along the length of a knife--since the blade won't follow (unless you have a circular blade)."

"AS A GUIDED SYSTEM follows the curve of the blade"

Please note subject vs. object.

Cynic2701 · Apr 2, 2014

Cynic2701 said:
Yes, "the angle changes as you swing the arm along the length of a knife--since the blade won't follow (unless you have a circular blade)."

"AS A GUIDED SYSTEM follows the curve of the blade"

Please note subject vs. object.

To be even more clear, I'm talking about the fact that if you wanted to keep the angles precisely the same (in order to avoid those small artifacts referenced by the OP) you have two obstacles:

1. The "wobble" of the arm of the system (e.g. on my Edge Pro the plastic piece that the arm moves back and forth through allows a small amount of up and down movement). Lagrangian, who you referenced, also has an interesting thread discussing the rigidity of guided systems.

2. That as the blade curves along its length (blade length), the arc length of the blade changes as the blade is moved either closer or further from the base of the arm (that is, where the arm attaches to the guided system). On an Edge Pro, after dialing in the angle and screwing it stopped, you can change the angle (even when measured by Angle Cube) by moving the blade closer to the base, or further away from the base. To put it another way, if you change the distance from which the blade is clamped onto the system, since the point that the arm is attached doesn't move, then the angle changes as the adjacent and hypotenuse change.

Edit: To be even more clear, since perhaps it's not obvious, but if you move the blade to "pivot" it so that the arc intersects at the same distance from the base of the system, it becomes difficult to do so because the OP's blade tapers towards the tip. If you look at the picture of their knife, despite the edge being straight for a portion, the blade becomes "narrower" towards the tip. This narrowing of the blade changes the distance between the point of contact of the sharpening stone on the system and the point on the system at which the arm is attached. This change produces a difference in angle.

cbwx34 · Apr 3, 2014

Cynic2701 said:
To be even more clear, I'm talking about the fact that if you wanted to keep the angles precisely the same (in order to avoid those small artifacts referenced by the OP) you have two obstacles:

1. The "wobble" of the arm of the system (e.g. on my Edge Pro the plastic piece that the arm moves back and forth through allows a small amount of up and down movement). Lagrangian, who you referenced, also has an interesting thread discussing the rigidity of guided systems.

2. That as the blade curves along its length (blade length), the arc length of the blade changes as the blade is moved either closer or further from the base of the arm (that is, where the arm attaches to the guided system). On an Edge Pro, after dialing in the angle and screwing it stopped, you can change the angle (even when measured by Angle Cube) by moving the blade closer to the base, or further away from the base. To put it another way, if you change the distance from which the blade is clamped onto the system, since the point that the arm is attached doesn't move, then the angle changes as the adjacent and hypotenuse change.

Edit: To be even more clear, since perhaps it's not obvious, but if you move the blade to "pivot" it so that the arc intersects at the same distance from the base of the system, it becomes difficult to do so because the OP's blade tapers towards the tip. If you look at the picture of their knife, despite the edge being straight for a portion, the blade becomes "narrower" towards the tip. This narrowing of the blade changes the distance between the point of contact of the sharpening stone on the system and the point on the system at which the arm is attached. This change produces a difference in angle.

Ah. A better explanation, thanks. Most of that really doesn't matter though, just be consistent in what you do.

I think the problem with the knife in the original post, is not setting a good bevel, then not spending enough time going thru the stones to clean up the edge. A resharpening with the shim he created, and working thru the stones again will most likely solve the problem (a path he was headed down anyway, so didn't think it was worth mentioning).

Monofletch · Apr 3, 2014

I just bought a new Edge Pro and I have noticed a HUGE difference in the SECOND knife I sharpened. It does take a bit too get use to how the mechanism works, but when you do it will make you say "WOW"!
I sharpened an 8crmov CRKT fixed blade first and it was..... strange... and it was like yours with scratches. I re sharpened that knife this morning (after trial and error) and the scratches are gone. I tried to use little or NO pressure and let the stone do all the work. A sharpie is your best friend when learning the Edge Pro. My Tenacious was easier to get right with the FFG, but the angle cube would save some time. Going to buy one today.....

I also ordered the little collar to adjust the angle when switching stones. It's easier than trying to eyeball it with each stone change.

My problem is the "slurry" scratches. I didn't read about that until after the fact. Lesson learned I guess.