Geometry and Kinematics of Guided-Rod Sharpening Systems

[Evil D]

As far as not moving the blade around, that really only makes a difference on very long blades. You have to go a few inches left or right of the table to start seeing wider bevels at the far ends. I also only make stokes into the edge unless I'm doing heavy stock removal reprofiling.

[jackknifeh]

@Evil D
I agree; if you don't move the blade in the EP, then the skill required is much less. Also, yeah, clamping properly on the WEPS takes a little time. Personally, I don't mind that. btw, if you do not move the blade in the Edge Pro, then it has many of the same effects where the sharpening angle will vary due to both the mechanism itself, and also due to the shape of silhouette of the knife (like the khukuri example above).

@Brock O Lee
Hmm... I haven't had much experience trying an EP. But it seems to me that on both a WEPS and an EP, it is fairly easy to do both leading and trailing edge strokes? I typically do leading edge strokes on my sharpening rig (see below).

@ everyone
I built my own sharpening rig, and it can be used in the style of an EP or a WEPS. And the knife can be fully clamped (WEPS), or un-clamped on a platform (EP).

Details on sharpening rig here:
http://www.bladeforums.com/forums/showt ... Pict-Heavy

Some pictures:

"Edge Pro Mode"


"Wicked Edge Mode"


Although I can do both, I usually prefer to use it in the WEPS mode.
Like Brock O Lee, I also like leading-edge strokes.

VERY cool setup you made there. Very cool. I congratulate you.

About your first paragraph and not moving the blade on an EP. I make what I call "Edge Guide Blocks" (EGB) for my knives that have a spine that results in the pivoting on the top of the spine where it contacts the guide. Spyderco's are the worst for this because of the hump for the opening hole. The blade will pivot back and forth on that spot making it more difficult to keep the edge angle at the belly and tip end consistant. The edge moving to different distances away from the blade table results in different angles. The difference is very small but when you are trying to put a perfect micro-bevel on an edge with a very high grit stone the angle NEEDS to be consistant. With a coarser stone stroking a micro-bevel that is VERY narrow the coarser stone will just create a new angle if one stroke is at 15 degrees, then the edge moves a tiny bit closer to the blade table and the next stroke is at 15.1 (or 2) degrees. But the very fine grit stones (4k and above for example) don't remove enough steel to create a whole new angle. You end up hitting only the top of the bevel not hitting the edge at all or hitting the edge at too high of an angle. A general believe I have is our angle consistancy needs to be more accurate as the grit gets higher. This is true with any system and free hand as well. Anyway, I make the EGBs. I make them out of plastic. The sit against the EP guide and the side against the blade spine is cut to the shape of the spine. Then I set the blade against the EGB and it stays in place throughout the stroke. I posted a thread explaining this in detail a long time ago. I'm sure I can find it (I think). That thread even has pictures. You do need an EGB for each different blade shape except once in a while. Sometimes the shape of one spine is close enough to another knife that one EGB is ok for both knives. This sounds like a pain to do but once you are used to making them it takes about 4-5 minutes to make one and the imporvement in the results is remarkable.

In case some EP users haven't thought about it the next time you use the EP to sharpen a knife with the Spyderco hole/spine is the only part of the blade that rests against the guide pay attention to how difficult it is to hold the blade perfectly still as you stroke from heel to tip while putting pressure on the edge. For me, holding the blade still is difficult. I was doing ok without the EGBs until I got my first ZDP-189 knife. With the harder steels the accuracy needs to be more consistant also because less steel is removed per stroke. This leaves us back to only hitting part of the bevel throughout a stroke. And since even less steel is being removed because it's harder our accuracy needs to be better. I'm having a hard time putting my thoughts down so it's easy to understand I thing. If there is anything someone doesn't understand pleas let me know. And if you have an EP I suggest trying the EGB thing. In fact if anyone has a knife I have I'll make you one and mail it to you to try.

Jack

[jackknifeh]

I found the thread for the EGBs I make if anyone is interested. It is titled "Edge Pro blocks for short blades". It has pictures. Sorry, buy you need to click on a .jpg file. I think I'll put the pics on photobucket. I'm using it now and love it for a fairly easy way to post pictures and of much better quality. You don't need to shrink the pics down as much.

http://www.spyderco.com/forums/showthre ... highlight=

[Laethageal]

Personally I don't use block. Instead I move the blade forward and backward on the EP, and rotate it so the edge I work on is about 2mm further then the end of the machine. So when I'm working on the tip, the tip is almost in the center, but the handle is pushed backward. With the belly of the blade you can't have it all horizontally anyway, so better move it slowly as you work you edge and stay close to the center so you keep about the same angle. The key is practice.

[jackknifeh]

Personally I don't use block. Instead I move the blade forward and backward on the EP, and rotate it so the edge I work on is about 2mm further then the end of the machine. So when I'm working on the tip, the tip is almost in the center, but the handle is pushed backward. With the belly of the blade you can't have it all horizontally anyway, so better move it slowly as you work you edge and stay close to the center so you keep about the same angle. The key is practice.

That is how we are supposed to use the EP. When I came up with the EGB idea it was because I couldn't hold my knife still that had ZDP-189 blade steel. I didn't understand why back then but it seemed the harder the blade steel is the more accurate the angle needs to be. Softer steels like AUS-8 don't require the precision because one stroke literally changes the angle of the bevel when I'm off by 1/10th a degree or so. But the harder steels may require 2, 3 or more strokes to remove the same amount of steel depending on how much pressure I use. This is what I believe and I think I'm right. Anyway, I was able to immediately sharpen the ZDP blade as soon as I had made the first block. So I just made blocks for any knife I wanted one for. Knives with a flat area on the spine that can rest against the guide don't require a block because the blade won't "pivot" on a flat spot. But now I have developed more consistancy when using the EP and maybe I could get away with not using the blocks. I may give it a try. While the blocks work perfectly I would rather not use them as long as I can get results just as good.

Jack

[Lagrangian]

@jackknifeh,
Thanks. Glad you liked the sharpening rig I made.
I like your idea of Edge Guide Blocks (EGB). I may have to make some. :)

@Evil D,
Oh, I mean that the shape of the knife, like how much belly the blade has, etc. will cause the sharpening angle to vary in the Edge Pro system (in much the same way it is affected in the Wicked Edge). I mean, this for when you don't move the knife, and even occurs on shorter knives. Depending on how pronounced the "belly" is, it could be more or less. I think it's probably a small effect for most knives, but I'll run some analysis to see how small.

btw, for the Edge Pro systems, swinging the sharpening stone to one side will typically increase the sharpening angle, while swinging to the opposite side will decrease the sharpening angle. For example, see the graph below, where the target angle is 15 degrees per side on a tanto blade. On one end of the knife, the angle goes greater than 15 degrees, while on the other end it goes below 15 degrees. The center of the platform is at X=0 inches. This graph is for the Edge Pro Apex.

[jackknifeh]

@jackknifeh,
Thanks. Glad you liked the sharpening rig I made.
I like your idea of Edge Guide Blocks (EGB). I may have to make some. :)

@Evil D,
Oh, I mean that the shape of the knife, like how much belly the blade has, etc. will cause the sharpening angle to vary in the Edge Pro system (in much the same way it is affected in the Wicked Edge). I mean, this for when you don't move the knife, and even occurs on shorter knives. Depending on how pronounced the "belly" is, it could be more or less. I think it's probably a small effect for most knives, but I'll run some analysis to see how small.

btw, for the Edge Pro systems, swinging the sharpening stone to one side will typically increase the sharpening angle, while swinging to the opposite side will decrease the sharpening angle. For example, see the graph below, where the target angle is 15 degrees per side on a tanto blade. On one end of the knife, the angle goes greater than 15 degrees, while on the other end it goes below 15 degrees. The center of the platform is at X=0 inches. This graph is for the Edge Pro Apex.

I don't understand your graph. But I think I know what you are getting at though. Is this it? The angle changes on knives with a lot of belly and you don't move the belly to the point directly in front of the blade table. Picture holding the knife in my right hand and the belly at the tip end is off the blade table on the opposite side of the blade table. With a lot of belly the top could be on the line of the blade guide. This means the distance from the edge right at the tip is less than it is on the edge directly in front of the blade table. There is a triangle formed by the blade table base, the vertical rod with angle marks and the stone rod. When you shorten the side of the triangle that is the blade table base because the tip is closer to the vertical rod than the edge is in the middle of the blade table, the angle where the stone and edge meet increases. I hope I explained my thoughts so it is understandable. Is this what you are talking about? I don't get what you mean about the angle increasing at one end of the blade and increases at the other end. Unless, you are talking about a tanto and the front edge to the tip. On a tanto the angle at the point where one straight section of the blade meets the other straight section is going to be lower than the angle created at the very tip. That is because the tip is closer to the vertical rod that the edges change. This is assuming the spine of the blade is resting against the blade guide. I have never sharpened a tanto blade but I've thought about how I might do it. I decided the way I'd try it would be to place the blade on the blade table with the front edge parallel with the front of the blade table. This way you could keep the angle on that portion of the edge about the same as the other section.

Did this make any sense?

On some knives when I use my EGB which holds the blade still, the angle changes a bit from heel to tip when there is even a slight curvature along the edge. I think the angle goes DOWN about 1 degree with the edge one inch off the end of the blade table. That's an approximation and also may differ when the EP is set at different angles.

Hopefully I made what I'm thinking clear enough that you can understand it. Even if I'm wrong.

Jack

[WorkingEdge]

I found the thread for the EGBs I make if anyone is interested. It is titled "Edge Pro blocks for short blades". It has pictures. Sorry, buy you need to click on a .jpg file. I think I'll put the pics on photobucket. I'm using it now and love it for a fairly easy way to post pictures and of much better quality. You don't need to shrink the pics down as much.

http://www.spyderco.com/forums/showthre ... highlight=

In trying to deal with the same problem, my low tech solution was cutting hard rubber washers/discs So the flat edge rests on the guide and the convex edge supports the spine to get the edge as parallel to the edgepro table edge as i want. there is minimal compression if the washer is hard enough. With the spine resting on two points, it's pretty stable.

[jackknifeh]

In trying to deal with the same problem, my low tech solution was cutting hard rubber washers/discs So the flat edge rests on the guide and the convex edge supports the spine to get the edge as parallel to the edgepro table edge as i want. there is minimal compression if the washer is hard enough. With the spine resting on two points, it's pretty stable.

That sounds like a good idea. I'm thinking if you rest a part of the spine on the guide while positioning the edge how you want it then put a cut washer between the guide and spine in a location where the spine makes no contact with the guide. That should hold the blade still throughout a stroke. However when flipping the knife the washer would need to be in the same place for the opposite side. Every time the knife is flipped the washer would need to be repositioned and if it is not positioned correctly the angle would change from the last stroke on that side. But using a piece of tape to tape the washer to the spine would solve this. Then the washer would always be at the same spot and the angle would remain consistant. When I flip the knife I also have to flip my EDGs. This felt a bit inconvenient so I remember taping the EGB to the spine before. But after a little practice flipping the EGB with the knife becomes just a part of the process and is quick. One thing I like about your idea is one washer could be used for different spine shapes. The washer would just need to be placed at the location appropriate for any given knife. Maybe twor three washers of different sizes would be all that is needed instead of my different blocks for almost every knife.

Jack

[Lagrangian]

@jackknifeh,

Can I nudge you to read the report? It's written for you and the knife community.
You'll really enjoy it; most of you intuition is on the right track. But I think you are missing a few pieces of the puzzle.

A picture is worth a thousand words, and a video is worth a hundred pictures. So please have a look? :)

Download Link:
https://drive.google.com/file/d/0B8rQYh ... Q2MlRFbTA/

Alternate Download Link:
http://www.mediafire.com/download/2flrq ... eta17).zip

[WorkingEdge]

my washer is placed at the edge of the guide so placement is the same each time. alternatively, could place a marker with a pen. does work but not as elegant as your method. :)

That sounds like a good idea. I'm thinking if you rest a part of the spine on the guide while positioning the edge how you want it then put a cut washer between the guide and spine in a location where the spine makes no contact with the guide. That should hold the blade still throughout a stroke. However when flipping the knife the washer would need to be in the same place for the opposite side. Every time the knife is flipped the washer would need to be repositioned and if it is not positioned correctly the angle would change from the last stroke on that side. But using a piece of tape to tape the washer to the spine would solve this. Then the washer would always be at the same spot and the angle would remain consistant. When I flip the knife I also have to flip my EDGs. This felt a bit inconvenient so I remember taping the EGB to the spine before. But after a little practice flipping the EGB with the knife becomes just a part of the process and is quick. One thing I like about your idea is one washer could be used for different spine shapes. The washer would just need to be placed at the location appropriate for any given knife. Maybe twor three washers of different sizes would be all that is needed instead of my different blocks for almost every knife.

Jack

[jackknifeh]

@jackknifeh,
Thanks. Glad you liked the sharpening rig I made.
I like your idea of Edge Guide Blocks (EGB). I may have to make some. :)

@Evil D,
Oh, I mean that the shape of the knife, like how much belly the blade has, etc. will cause the sharpening angle to vary in the Edge Pro system (in much the same way it is affected in the Wicked Edge). I mean, this for when you don't move the knife, and even occurs on shorter knives. Depending on how pronounced the "belly" is, it could be more or less. I think it's probably a small effect for most knives, but I'll run some analysis to see how small.

btw, for the Edge Pro systems, swinging the sharpening stone to one side will typically increase the sharpening angle, while swinging to the opposite side will decrease the sharpening angle. For example, see the graph below, where the target angle is 15 degrees per side on a tanto blade. On one end of the knife, the angle goes greater than 15 degrees, while on the other end it goes below 15 degrees. The center of the platform is at X=0 inches. This graph is for the Edge Pro Apex.

Your graph is wrong. Or, I'm not reading it correctly. Probably the second option. :) I'm sure I am missing some pieces. Mom always told me I was a few pieces short of a jigsaw puzzle. :)

Is the hypothetical blade edge straight? Where is X when it equals zero? I'm picturing my 10" plain edge, straight (no belly) edge knife sitting on the EP blade table with the 5" point in the middle of the blade table. The EP is set to 15 degrees (per side). If your graqh is based on an EP with a knife in this position I don't understand your graph. If the degree is 15 when sitting on the edge at the center of the blade table I'm considering that zero. If swinging the stone means moving it toward the heel or the tip of the blade the angle will DECREASE more and more the farther you move the contact point away from zero.

In my mind the only way to move the stone arm and still keep the edge angle the exact same would be to take a circle and surround the vertical post with it. The outside of the circle will sit on the knife edge in the center of the blade table. To keep the angle exactly the same the blade would need to be shaped just like the outside of the circle. Or, you would need to move the blade so you are always stroking within the outsides of the blade table. Keeping the strokes between the outsides of the blade table I think is how Mr. Dale intended the EP to be used.

Another question. Why do you use the term "dihedral angle"? This refers to a figure formed by two planes intersecting. Yes, I had to look it up. :) This means to me that we need to picture a 3 dimensional angle picture instead of one with 2 dimensions. On the EP I picture looking at the angle from the side of the EP. The angle is formed by the blade table and the stone surface with no "depth". By using the word dihedral I'm picturing a plane (instead of a line) formed by the blade table and the stone surface. Did that make any sense? Am I right? And most importantly how does this apply to sharpening my pocket knife??? These may be some of the pieces I'm missing (which doesn't surprize me BTW).

I'm not actually suggesting you are wrong. I'm saying I don't know what you are talking about. This is not the first time I haven't understood something some one says when they are more educated than I am about something.

Jack

[Lagrangian]

@jackknifeh,

The answer to your questions are in the report. :)

[jackknifeh]

@jackknifeh,

The answer to your questions are in the report. :)

I will look at it tomorrow morning. I'm on my tablet now and can't look at it. Looking forward to it.

Jack

Edit
It's very possible I won't understand the report if it deals with geometry at a higher level than 10th grade. :) I think that's the last time I had geometry. If I took a class later it's obvious I didn't learn anything. :)

[jackknifeh]

I might have just figured something out. I started touching up my GB on a bench stone (Spyderco UF). When free hand sharpening I do look at the big picture as the surface of the stone and the knife blade as two PLANES intersecting at the contact point. I don't picture the angle I'm trying to maintain as two single lines. The angle is comprised of two planes. I picture the entire stone surface and the entire side of the blade. Actually, it's the line (plane) through the center of the blade. Is this it??? :confused:

[Lagrangian]

In some more detail:

In the report, there is an entire chapter on dihedral angles. They are defined in Chapter 2, and some of the ways they can be changed are also described.

Many different effects are occuring simultaneously, including:
(1) Position of the contact point between the stone and knife.
(2) Where the contact point is on the stone surface.
(3) Orientation of the knife edge at the contact point. This is affected by the belly of the knife.
(4) The pivoting mechanism of the sharpener (EP Apex, EP Pro, WEPS-Gen1, WEPS-Gen2)
(5) Fairly complicated interactions between (4) and (1) - (3)

It is pretty much impossible to analyze all of this without a solid understanding of dihedral angles. That is why they are discussed right after the introductory chapter.

From the geometry shown in the report videos, it becomes obvious that the graph above has the correct overall shape. Namely, when sharpening a knife with a straight edge (like a tanto), that one side will have a slightly larger angle, and the other side will have a slightly smaller angle (when sharpening on an EP-Apex). This effect disappears if the EP's pivoting mechanism is replaced with a spherical joint, or a gimble (like the gimble in the universal joint of a truck's transmission). (See Chapter 3 for details.) However, using a spherical joint only simplifies (4) somewhat. Effects from (1) - (3) are still present and significant.

If you want to understand why, then go read the report. :)

In a well-defined technical discussion, like this one, there is a definite answer. The only questions are how to find it, and what proofs or evidence are convincing?

Suppose I give a mathematical proof. Is that convincing? No, not for most people in the knife community because they are mostly not from technical backgrounds, like science, math, or engineering. (My own background is in physics and computer science.) To many, a mathematical proof would either be something they did not fully understand, or would not be able to check for correctness.

This is why the report mostly avoids math. Instead, about two thirds of the report are figures and animations.

Of course you are free to disagree! :) But if you want to engage in dicussions that actually have meaning, then we should carefully understand what each of us is saying. And about 95% of what I wish to show is in the report, and is explained there about the best I can, given my limitations in time and format. Certainly, it is explained better in the report than I could do here in a forum post.

Sincerely,
--Lagrangian

[jackknifeh]

I might have just figured something out. I started touching up my GB on a bench stone (Spyderco UF). When free hand sharpening I do look at the big picture as the surface of the stone and the knife blade as two PLANES intersecting at the contact point. I don't picture the angle I'm trying to maintain as two single lines. The angle is comprised of two planes. I picture the entire stone surface and the entire side of the blade. Actually, it's the line (plane) through the center of the blade. Is this it??? :confused:

Been thinking about it some more and maybe I do picture the contact point (stone to edge) as two planes when using the EP. As I round the belly to the tip I "spin" the stone rod. This keeps the two planes at the correct angle if I "spin" accurately. The difference between this and free hand is I'm not keeping the edge at contact point perpindicular with the direction I'm stroking when using the EP. Whan free hand sharpening I try to keep the scratch pattern always at a 90 degree angle with the edge as I stroke around the belly to the tip. Did this make sense?

Jack

Edit:
Changing the angle of the scratch pattern can effect the cutting performance of a toothy edge I've heard. It's like a hacksaw blade. It cuts better when the teeth face forward in the cutting direction. So if you want the edge to cut better when slicing with pull strokes you change the scratch pattern direction appropriately. I've never experienced this difference. Never tried so I'm just repeating what I've read.

Jack again. :)

[Lagrangian]

I will look at it tomorrow morning. I'm on my tablet now and can't look at it. Looking forward to it.

Jack

Edit
It's very possible I won't understand the report if it deals with geometry at a higher level than 10th grade. :) I think that's the last time I had geometry. If I took a class later it's obvious I didn't learn anything. :)

Hi Jack,

If parts of the report are hard to understand, then I'm happy to discuss and/or try to explain them better. Just ask me. :) I can't promise that I'll come up with something better, but I'll try!

[jackknifeh]

Hi Jack,

If parts of the report are hard to understand, then I'm happy to discuss and/or try to explain them better. Just ask me. :) I can't promise that I'll come up with something better, but I'll try!

Ok, I've read enough to eagerly back out of any intelligent discussion of the info in the report. The math is beyond my education level and to be honest I have no desire to learn the math enough to understand this report. There is one thing I read right off when I saw the chapter title. The issue of the stop collar being an approximation. I already knew this and have mentioned it in this forum. However, I didn’t know why. I had guessed and attributed the slight inaccuracy to my human error or the fact that since the collar is slightly larger than the rod there could be some twisting involved when I tighten the set screw. When the collar is perpendicular with the rod the setting would be accurate. But when I tighten the screw I twist the collar. This will cause one side to rise above the perpendicular line, changing the angle. Now that I know it is a geometrical problem I can now assume I have no human error at all. :rolleyes: :) I noticed the inaccuracy only in the higher grit stones because they remove such a small amount of steel on each stroke. Therefore I could re-set the angle for a new stone and perform one stroke for angle testing. The coarser stones (500 to 1k for example) removed enough steel with one stroke so the scratch pattern and new angle completely replaced the old angle. However with the finer grit stones they only removed enough steel that only the top (or bottom, don’t remember) of the bevel would show the new angle. Then I would make a micro adjustment of the angle so now my 8k stone matches the same angle as the 4k. This micro adjustment sometimes has taken two or three changes. That’s why I don’t remember which part of the bevel shows the new angle first.

I don’t understand the math but I already did know there was a slight inaccuracy with the stop collar trick. So, since I also don’t understand the math and dihedral angles thoroughly I will assume with confidence that the rest of the information is accurate. I’m going to go through the report up to and including the EP and stop collar trick chapters. I may get some of it. Let me assume something. I assume to design and manufacture a machine that is completely accurate would come with a price tag to match. Accurate with the exception of different blade shapes. This would not be a constant.

I watched some of the videos first. After going through them I knew more was going to be discussed than I had ever thought about before. And I have to say that without the videos the material would be hard for most people, and impossible for me to understand. Grasping a concept has proven hard for me when it is only in writing. But when I can see it or better yet touch or do something I can then “get it”.

Congratulations on the thoroughness of this report. It’s not essential to getting very sharp edges using the EP or WE. BUT, for getting the hair whittling, super sharp, crisp, straight razor sharp edges this level of knowing the tool is essential I believe. My knowing the problem with the collar issue and correcting for it is an example. Understanding the math isn’t required but if I did understand everything in the report I would have known of different issues after reading this report. Then purchasing an EP I could have overcome some of the inaccuracies much sooner while learning to use the tool (Edge Pro). OTOH, after reading the report I probably would have kept using the DMT aligner. :)

What I am loving is using the EP and using bench stones both. One major difference in the two methods is with bench stones I can see the blade/stone contact point. With the EP I can't. This makes it especially hard to keep the angle perfect right up to the very end of the tip. The tip of the blade is the most difficult part of using the EP because it can't be seen. Well, for me it's the most difficult issue.

Excellent report. Defenately a head scratcher. :D

Jack

[Lagrangian]

Hi Jack,

Thanks for having a look at the report. Sorry if it's a bit complicated, but I'm glad the videos helped and that you found some parts of it to be useful. :)

The report may be more interesting than it is useful. The slight variances in angle that are due to a perfect mechanism are probably smaller than variances due to the fact that real parts must be slightly inaccurate. For all practical purposes, the Edge Pro and the Wicked Edge are very accurate, consistent, and repeatable.

It is a little bit like driving your car. It's cool to learn about how it is designed and engineered, but that won't make you a great driver. Similarly, the report is a theoretical analysis of sharpening mechanisms, but that has very little to do with being a great sharpener. :)

Still, it might be useful for anyone who wants to design and make their own sharpeners.

Sincerely,
--Lagrangian

P. S. I'm running a few more analyses and will post those results soon.