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TOPIC: Geometry and Kinematics of Guided-Rod Sharpeners

Geometry and Kinematics of Guided-Rod Sharpeners 7 months 3 weeks ago #14963

  • AnthonyYan
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Hi Everyone,

I've performed a very detailed mathematical analysis of the Edge Pro Apex (EP-Apex) and also the Wicked Edge Precision Sharpener (WEPS). I wanted to share the results with the general knife community.

As someone who loves mechanisms, I wondered if there are any ways to improve the EP or WEPS. Of course one could improve the precision of the EP and WEPS mechanisms with more accurate parts machined to a finer tolerance, etc.

However, after careful thinking, I realized that even if these mechanisms were _perfectly_ precise and _infinitely rigid_, that they would not always grind a perfect dihedral angle (informally known as a "V-edge"). That is, if we used a perfect EP or WEPS to sharpen a tanto knife, then the knife edge would not have a perfectly uniform dihedral angle. There will be a tiny variation in the included angle of the knife bevel.

How big is this variation in angle? To study it, I coded a computer program calculate the geometry and have written up the results here.

Topics in the report include:
(1) Tiny variations in sharpening angle in the Edge Pro Apex and also the Wicked Edge Precision Sharpener.
(2) A detailed analysis of the "Stop-Collar Trick" and how it is an approximation.
(3) For WEPS sharpening, a discussion about where to clamp the knife so that the sharpening angle is as uniform as possible over the entire knife edge.
(4) Using belt sanders to sharpen V-edges.

To pique your interest, here are some figures and one animation from the technical report.

Sample Figures:
imgur.com/a/1J8GP#0








Sample Animation on YouTube:



The full report is currently an initial draft (version 1.0.beta17), and it can be downloaded here:
drive.google.com/file/d/0B8rQYhU8N9ZGSENqc2Q2MlRFbTA/

Alternate Download:
www.mediafire.com/download/2flrqn7po9um3...DRAFT_1.0beta17).zip

The link is to a .zip file on Google Docs. The .zip file contains:
(1) A PDF file with embedded videos.
(2) Separate video files in a directory named "Movies"
(3) README file
(4) Creative Commons License file

The .zip file is huge because it contains many animation videos and figures. To view the animations within the PDF file, it is recommended that you use Adobe Reader version 9.0 or latter. Other PDF viewers will probably not play the videos. Also, you may have to give Adobe Reader permission to play the videos. If your PDF viewer cannot play videos, you can still view the .mp4 files in the folder "Movies." These files are .mp4 videos (MPEG-4/H.264) and can be played with free software such as Apple's QuickTime Player and/or VideoLAN, etc.

Please note: the slight variation in sharpening angle is VERY SMALL. In fact, it is typically around 0.1 degrees or less. In the worst case that is plausibly realistic, it is at most 0.5 degrees. In the Sample Figures above, we only really care when the sharpening stone is close to position X=0 inches, that is -1" <= X <= +1". These TINY changes in sharpening angle are virtually undetectable in practice.

Therefore this report is only interesting to:
1. Knife sharpening fanatics who like V-edges.
2. Engineers who like to study mechanisms.
3. Those of us who are insane. :)

This is still a beta version draft, so feedback is welcome.
If you have any questions, suggestions, or constructive criticism, just post to the discussion.

Sincerely,
--Anthony "Lagrangian" Yan

"What grit sharpens the mind?"
--Zen Sharpening Koan
Last Edit: 5 months 2 weeks ago by AnthonyYan. Reason: 1.0beta17
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Geometry and Kinematics of Guided-Rod Sharpeners 7 months 3 weeks ago #14964

  • LeoBarr
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In an effort to make the EP pro a more precise tool I installed this rod end bearing this coupled with a drill stop collar makes for precise tracking .
I await the SWATS for the WE to increase the accuracy particularly when changing stone mediums - currently to be really accurate it is necessary to check settings when changing to different sharpening mediums diamonds-Choseras/Ceramics .
Looks as if my WE is in Spanish customs hopefully if they like the paperwork and accept the tax and handling payment I should have it within days!
IMG_1457.jpg
Last Edit: 7 months 3 weeks ago by LeoBarr. Reason: SPELLING
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Geometry and Kinematics of Guided-Rod Sharpeners 7 months 3 weeks ago #14965

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Hi LeoBarr,

I also think using a spherical rod-end is a good idea. A mathematical analysis shows that it is one way to improve the accuracy the the Edge Pro (at least in theory). The technical report uses a photo from MadRookie that shows his modification of his Edge Pro which is very similar to yours. I also use spherical joints in my home-built sharpening rig.
www.bladeforums.com/forums/showthread.ph...d-ApexPro-Pict-Heavy

It is possible to use regular hinged joints (like the ones in the original WEPS) to be mathematically perfect, but in practice it involves arranging the joints in a gimbal, and that has more moving parts than a simple spherical rod-end. So the gimbal arrangement may not be worth it. (More discussion about spherical rod ends and gimbals is in the report's chapter on the Edge Pro.)

The stop-collar trick is an approximation, so it's not 100% accurate. But if you are sharpening near 15 degrees per side on the Edge Pro Professional, or 30 degrees per side on the Edge Pro Apex, then the stop-collar trick becomes virtually nearly perfect (the error is too small to be noticed in practice, and the error actually goes to zero if you are sharpening exactly at these angles).

When sharpening at angles different from these (15 degrees for EP-Pro, 30 degrees for EP-Apex), I was wondering what would be a way to compensate for stone thickness that would be mathematically perfect. So far, I haven't thought of something that would be worth it; even though the "stop collar trick" is an approximation, it is a very good approximation. So, a better way would have to be even simpler to use and mechanically robust to be worth the extra 0.05 degree accuracy. I thought of a way, but it was too complicated and not as robust. Only matters if you care about accuracy better than around 0.05 degrees.

If you are curious, the sample image about the Stop Collar Trick shows why it is an approximation. (Or you can look at the chapter about the Stop Collar Trick.)
Last Edit: 7 months 3 weeks ago by AnthonyYan.
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Geometry and Kinematics of Guided-Rod Sharpeners 7 months 3 weeks ago #14966

  • tuffybraithwaite
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AnthonyYan wrote:
Hi LeoBarr,

I also think using a spherical rod-end is a good idea. A mathematical analysis shows that it is one way to improve the accuracy the the Edge Pro (at least in theory). The technical report uses a photo from MadRookie that shows his modification of his Edge Pro which is very similar to yours. I also use spherical joints in my home-built sharpening rig.
www.bladeforums.com/forums/showthread.ph...d-ApexPro-Pict-Heavy

It is possible to use regular hinged joints (like the ones in the original WEPS) to be mathematically perfect, but in practice it involves arranging the joints in a gimbal, and that has more moving parts than a simple spherical rod-end. So the gimbal arrangement may not be worth it. (More discussion about spherical rod ends and gimbals is in the report's chapter on the Edge Pro.)

The stop-collar trick is an approximation, so it's not 100% accurate. But if you are sharpening near 15 degrees per side on the Edge Pro Professional, or 30 degrees per side on the Edge Pro Apex, then the stop-collar trick becomes virtually nearly perfect (the error is too small to be noticed in practice, and the error actually goes to zero if you are sharpening exactly at these angles).

When sharpening at angles different from these (15 degrees for EP-Pro, 30 degrees for EP-Apex), I was wondering what would be a way to compensate for stone thickness that would be mathematically perfect. So far, I haven't thought of something that would be worth it; even though the "stop collar trick" is an approximation, it is a very good approximation. So, a better way would have to be even simpler to use and mechanically robust to be worth the extra 0.05 degree accuracy. I thought of a way, but it was too complicated and not as robust. Only matters if you care about accuracy better than around 0.05 degrees.

If you are curious, the sample image about the Stop Collar Trick shows why it is an approximation. (Or you can look at the chapter about the Stop Collar Trick.)
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mr yan
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1 fine looking set up u have there. amazing
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<"))))><(
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Geometry and Kinematics of Guided-Rod Sharpeners 7 months 3 weeks ago #14967

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Thank you for that I actual was inspired by Madrookies set up and have mailed him several times on the finer points of the EP & his vast experience of lapping he actually checks his stones with a digital vernier to ensure they are flat and he was also very helpful with his experience with Atoma plates they he recommends bevelling off all corners as one should do with all stones.
Madrookie has been working with Mark from CKTG on a kit including the rod end bearing solution and it is he who made the You Tube video explaining the use of the drill stop collar which becomes more and more important the lower the sharpening angle is ; in fact the drill stop collar does not fit on the scissor attachment but the inaccuracies caused by different stone thicknesses is negligible at such big angles; the sharpening tapes concur with this whereas on knife sharpening angles even the slightest difference in angles are enough to cause the tape to be ripped by the blade.
I look forward to the WE equivalent of the drill stop collar since the results certainly without the DSC on the EP the blade just does not get that sharp I suspect that could be the same on the ~WE when using different stone mediums.
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Geometry and Kinematics of Guided-Rod Sharpeners 7 months 3 weeks ago #14968

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I will second Tuffy's remarks I like the fact that it will work in both WE & EP mode as you say each system has advantages which I will very soon have both .
I am also able to get very good results on a variety of bench stones often the handle of the knife or thumb studs for opening knives gets in the way on guided rod systems and high end Japanese knives are best done on bench stones especially Debas which may have two different bevels & then of course the Uriashi sharpening on the back (Uri) of the knife which is very important for any chisel edged Japanese knife.
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Geometry and Kinematics of Guided-Rod Sharpeners 7 months 2 weeks ago #14988

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Some interesting discussion about the WEPS and recurve blades on BladeForums.com. Thanks to brplatz for his ideas and observations. Perhaps the solution suggested is cumbersome, but I was surprised and amused by it.

www.bladeforums.com/forums/showthread.ph...2922018#post12922018

Here is a diagram I made for the discussion at the link above.
Last Edit: 7 months 2 weeks ago by AnthonyYan.
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Geometry and Kinematics of Guided-Rod Sharpeners 7 months 2 weeks ago #14990

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Hi Everyone,

Here is the latest version of the technical report, with a new section on recurve blades with ideas suggested by brplatz.

Download:
drive.google.com/file/d/0B8rQYhU8N9ZGSENqc2Q2MlRFbTA/

Alternate Download:
www.mediafire.com/download/2flrqn7po9um3...DRAFT_1.0beta17).zip

Sincerely,
--Lagrangian
Last Edit: 5 months 2 weeks ago by AnthonyYan. Reason: 1.0beta17
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Geometry and Kinematics of Guided-Rod Sharpeners 7 months 1 week ago #15022

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btw, I've released the technical report under a Creative Commons License, so feel free to add it to the Wicked Edge Wiki.
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Geometry and Kinematics of Guided-Rod Sharpeners 7 months 1 week ago #15024

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So...I read this.
Then read it again, following the links.
You're all crazy.
I love you all.
Ahhhh, family.
“On one otherwise normal Tuesday evening I had the chance to live the American dream. I was able to throw my incompetent jack*ss of a boss from a fourteenth-story window.”

Owen Pitt – Monster Hunter International
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