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TOPIC: Stroke Direction

Stroke Direction 1 year 2 weeks ago #13433

  • wickededge
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Mikedoh wrote:
Could the edge trailing be leaving a bit of a burr?

I was curious about this as well so took both blades under the microscope at 2000x. In the back of my mind I had an alternate theory and what I saw under the scope may confirm it:

h485771a.jpg

100# Diamond Plates - Edge Trailing Strokes 2000x Magnification

h383b0f7.jpg

100# Diamond Plates - Edge Leading Strokes 2000x Magnification

I was fascinated to see the toothy appearance of the edge sharpened with leading strokes.

* Please disregard the legend at the bottom of the pictures. I'd forgotten to switch the magnification in the scope software so it's reading lengths as though they were at 800x instead of 2000x.
--Clay Allison
Last Edit: 1 year 2 weeks ago by wickededge.
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Stroke Direction 1 year 2 weeks ago #13434

  • JameyHoward
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Very interesting, I would have thought that edge trailing would have given more teeth. For some reason my natural assumption was that edge leading would flatten the peaks (teeth) more but I guess it doesn't.

But teeth only help with slicing, not push cutting. How does your sharpness testing Jig work? Does it press down flat (no slicing) or does it move the knife in a sawing motion? Sorry if that's been answered elsewhere, I did look at the specs for the sharpness tester but to be honest it was a bit above my head so I gave up :)
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Stroke Direction 1 year 2 weeks ago #13435

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JameyHoward wrote:
Very interesting, I would have thought that edge trailing would have given more teeth. For some reason my natural assumption was that edge leading would flatten the peaks (teeth) more but I guess it doesn't.

But teeth only help with slicing, not push cutting. How does your sharpness testing Jig work? Does it press down flat (no slicing) or does it move the knife in a sawing motion? Sorry if that's been answered elsewhere, I did look at the specs for the sharpness tester but to be honest it was a bit above my head so I gave up :)

I was assuming more teeth from edge trailing as well which is why the images surprised me. The sharpness testing jig works by applying downward force on the blade. There is no slicing motion. I'm thinking that the force is being concentrated on the tallest of the teeth, resulting in a much greater force per distance of blade on the peaks and rupturing the tape more easily. With the smoother blade from the trailing strokes, the force would be more evenly distributed requiring greater force to rupture the tape. I can definitely see the need for additional tests for cutting ability with each grit/stroke direction i.e. does one shave better than another, push cut paper etc...?
--Clay Allison
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Stroke Direction 1 year 2 weeks ago #13436

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An easy test just confirmed that the toothier, edge leading blade slice cut copy paper extremely well but gave a very rough push cut through the paper. The edge trailing blade gave a much cleaner result with the push cut but did not perform as well with the slice cut. Not too surprising.
--Clay Allison
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Stroke Direction 1 year 2 weeks ago #13437

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Toothy because the diamonds are hitting the edge creating depressions? The areas between the teeth look fairly consistent in size... maybe they correspond to the diamond size.

Be interesting to see what the finer stones and ceramics look like.
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Stroke Direction 1 year 2 weeks ago #13438

  • EamonMcGowan
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wickededge wrote:
JameyHoward wrote:
Very interesting, I would have thought that edge trailing would have given more teeth. For some reason my natural assumption was that edge leading would flatten the peaks (teeth) more but I guess it doesn't.

But teeth only help with slicing, not push cutting. How does your sharpness testing Jig work? Does it press down flat (no slicing) or does it move the knife in a sawing motion? Sorry if that's been answered elsewhere, I did look at the specs for the sharpness tester but to be honest it was a bit above my head so I gave up :)

I was assuming more teeth from edge trailing as well which is why the images surprised me. The sharpness testing jig works by applying downward force on the blade. There is no slicing motion. I'm thinking that the force is being concentrated on the tallest of the teeth, resulting in a much greater force per distance of blade on the peaks and rupturing the tape more easily. With the smoother blade from the trailing strokes, the force would be more evenly distributed requiring greater force to rupture the tape.

Clay,
I am still waiting for the triple beam to be built for my jig. My collar is on a wood dowel that I apply the pressure to. To support your theory? All of a sudden the knife being tested was giving readings of about 10 grams and I was like what the heck? What I had one is slipped down into the serrated part of the blade. The serrations took almost no pressure to cut the tape? I think you are absolutely right that the peaks and valleys make it easier to cut the tape. Hence a "sharper blade"?
The pics are fantastic! I too was wondering what the edge leading vs edge trailing looked like? You do some great testing! Thank you,
Eamon
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An old Irish toast, May the wind always be at your back, may you always have work and may you be in heaven a half hour before the devil knows your dead. Cheers!
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Stroke Direction 1 year 2 weeks ago #13439

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I decided to check what a little stropping would do to the Edge Trailing blade so I completed 20 strokes with the 14um strops and ran a test series. There was a 12% performance decline after stropping so I took it to the scope:

h4f4f8bf.jpg

14um Diamond on Cow Leather Strops after 100# Diamond Plates - Edge Trailing Strokes 2000x Magnification

I also tested it with both push cutting and slice cutting through copy paper - not much difference that I could tell. I then checked it for shaving and that's where I saw a large difference. It shaved significantly more easily than either the Edge Trailing or Edge Leading blades.

For reference, here is a nice shot of a blade I stropped down to .25um on kangaroo leather:

h85cae72.jpg

.25um Diamond on Kangaroo Leather Strops - 2000x Magnification
--Clay Allison
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Stroke Direction 1 year 2 weeks ago #13440

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I decided to run a few tests on the .25 kangaroo stropped blade since we were looking at edge straightness vs. point sharpness. It shaved amazingly well, push cut copy paper like nobody's business and would hardly slice cut the copy paper. In the sharpness jig, it required 27% more force to cut the tape than the Edge Trailing 100# blade and 30% more force than the Edge Leading blade.
--Clay Allison
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Stroke Direction 1 year 1 week ago #13441

  • razoredgeknives
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wickededge wrote:
I decided to run a few tests on the .25 kangaroo stropped blade since we were looking at edge straightness vs. point sharpness. It shaved amazingly well, push cut copy paper like nobody's business and would hardly slice cut the copy paper. In the sharpness jig, it required 27% more force to cut the tape than the Edge Trailing 100# blade and 30% more force than the Edge Leading blade.

Man... That is really strange, exactly opposite what I would have thought. Any ideas as to why?
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Stroke Direction 1 year 1 week ago #13442

  • PhilipPasteur
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I have been following this thread...and the original on the sharpness tester. Just have had no time free to respond. Still slammed at work...

Anyway I am finding this very intriguing. I think we will get back at some point to discussing the whole concept of "what is sharp". I think Clay's idea of the concentration of force on the teeth making the readings different makes very good sense to me.

I, personally believe that I would prefer the Kangaroo .25 micron stropped blade if I was looking for something that I consider to be sharp. This does not mean that I don't think that there is a set of circumstances where an edge with some tooth might be preferable, but if we are trying for the most refined edge possible ... an edge that is as fine as the steel will support, a toothy edge is not it!

To me, this calls into question the general utility of the tester for determining what is sharp, at least using my definition. I wonder how an obsidian scalpel would test. Maybe not as well as a 100 grit leading stroke blade... but really, which is sharper??

Of course, I could see where it could help in judging the relative sharpness of blades sharpened using the same set of techniques and grits... perhaps answering the question "am I doing this correctly with the best technique for the grits I am using". But it seems at this point that the absolute numbers do not necessarily agree with what I am looking for when I am trying for the "perfect" edge...

I am sure there is more to come... but that is what I am feeling right now.
Phil

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Last Edit: 1 year 1 week ago by PhilipPasteur.
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