Sharpness Testing JigI’ve been discovering some fascinating things by using the designed by BassLakeDan. The first thing I did was to establish some baseline values for the different grits of diamond plates we offer. In the process, I decided to test what effect, if any, the stroke direction might have. What I found surprised me; over all the grits I’ve tested so far (100#, 200#, 400#, 600#, 800# and 1000#) I’ve found that there is an approximately 20% sharpness improvement by sharpening into the blade as opposed to away from it. A typical data set looks like the following attachment: [url url=http://www.wickededgeusa.com/files/Sharpness by Grit - Diamond Stones.pdf]Sharpness by Grit - Diamond Stones.pdf[/url]
Still left to test (hopefully today) is whether sharpening away from the blade throughout the progress and then finishing with a few strokes into the blade yields the same results as sharpening into the blade throughout. Sharpening away from the blade is much safer and faster, so being able to continue to do so and finish with a few light strokes into the blade would be idea.
That is interesting. Wonder if it translates to the ceramics too… I’ll often switch to edge leading when I get to those. Always thought they were sharper at the end… be interesting to see if the numbers back it up.
I think I asked before but can’t find it… have you done anything to see what the numbers correspond to? For example at XXXg it will slice at XXXg it will pushcut, etc.
Nice addition you made too (from the other thread).
Good questions Curtis. I’m guessing it will translate to the ceramics too though I won’t speculate until I’ve actually tested it.
I don’t remember if you asked about the other tests though it is a great idea. Maybe a series of tests after using the jig like Hanging Hair Test, Push Cut Copy Paper, Slice Cut Copy Paper etc… Those would be pretty easy to add into the sheet for each grit/angle.
[quote quote=“JameyHoward” post=13418]Interesting. Is it worth also trying a scrubbing motion rather than pure upstokes or pure downstrokes? Or would that be futile?
After you’d finished the progression and did the final grit, how many strokes did you do with the final stone?
And 34 complete progression sharpenings on the 600 grit stones alone? Wow, this must have taken you ages.[/quote]
I was also wondering about testing the scrubbing though I’m not sure it would work well. I say that because whenever I’m finishing a knife, I find that anything beyond alternating from side to side, one stroke at a time, raises a burr and I think that would decrease the sharpness. Still, it’s a great question and definitely worth testing. I think we’d need to establish exactly how long one scrubs or uses a circular motion per side. Another thing I’d like to test is what effect sharpening parallel to the edge has.
That’s a very interesting observation! I normally use sweeping passes up and away from me until I get to the final stone and then use edge leading passes from the heel to the tip. Maybe I have been getting the optimal edges all along!
I know that it makes a HUGE huge difference in cutting ability if you maximize the direction of your grind for the way the knife is used.
[quote quote=“razoredgeknives” post=13426]That’s a very interesting observation! I normally use sweeping passes up and away from me until I get to the final stone and then use edge leading passes from the heel to the tip. Maybe I have been getting the optimal edges all along!
I know that it makes a HUGE huge difference in cutting ability if you maximize the direction of your grind for the way the knife is used.[/quote]
I’ve been using the exact same technique for a long time and it has always appeared to work best. It’s nice to see it quantitatively as well.
I just ran a quick test of a blade that was prepared with 100# diamond plates and edge trailing motion. I then applied 10 strokes each side with the 100# plates and edge leading motion. Here are the results:
Edge Trailing AVG = 276g (Averaged from 10 measurements)
Edge Leading AVG = 235g (Averaged from 10 measurements)
Difference = 15% less force needed after 10 Edge Leading strokes applied per side
I’ll do a lot more testing but it does seem to be effective to do the bulk of the progression with edge trailing strokes and then switch to edge leading strokes with the last stone, maybe even the last 10-20 strokes with the last stone.
I took the previous test a step further and completed an additional 5 Edge Leading strokes per side and then took another 10 measurements. Here are my results:
Edge Leading AVG = 223g (Averaged from 10 measurements)
The additional 5 strokes per side brought us to a 19.4% improvement from the original blade that was prepared using only Edge Trailing strokes.
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:
[color color=#0000ff]100# Diamond Plates - Edge Leading Strokes 2000x Magnification[/color]
I was fascinated to see the toothy appearance of the edge sharpened with leading strokes.
[color color=#0000ff]* 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.[/color]
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
[quote quote=“JameyHoward” post=13434]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 :)[/quote]
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…?
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.
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.
[quote quote=“wickededge” post=13435][quote quote=“JameyHoward” post=13434]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 :)[/quote]
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. [/quote]
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
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:
[color color=#0000ff]14um Diamond on Cow Leather Strops after 100# Diamond Plates - Edge Trailing Strokes 2000x Magnification[/color]
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:
[color color=#0000ff].25um Diamond on Kangaroo Leather Strops - 2000x Magnification[/color]
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.
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.
