New testing session.

[Razorsharp244]

nozh2002 - It is that very pressure while cutting that I'm talking about. If greater cutting pressure results in greater edge wear then blade geometry could be having as great or greater influence on edge retention than steel composition. The only way to know for sure would be to eliminate blade geometry as a variable by comparing only flat grinds or hollow grinds, etc.

One way to do this would be to present the results with and without geometry taken into consideration. Like a result "matrix". This way you can use your previous results (if you remember what grinds they were) and map them in a "total list" like the one you have, one "flat ground list" and one "hollow ground list". And maybe even a "22 deg" angle list and a "15 deg angle list". After that when you watch the different lists at the same time it would be fairly easy to predict the influence of grinds.

Different ways of presenting your data, without additional testing. Just a suggestion.
//Jerker

 

[antonio_luiz]

Probably well beyond the scope of most members but high mag images of the edge during the testing process (scanning EM?) may help explain why some knives seemed to improve as they were used

I should also noted that all these tests were on manila rope. Cutting other materials may have produced very different results

 

[Dog of War]

Probably well beyond the scope of most members but high mag images of the edge during the testing process (scanning EM?) may help explain why some knives seemed to improve as they were used

I should also noted that all these tests were on manila rope. Cutting other materials may have produced very different results

Yes, comparing nozh's data to results of my own testing finds some radical discrepancies. I suspect different sharpening methods and edge geometry explain much ... I was surprised at the rapid loss of sharpness nozh measured with certain steels after only a few cuts. IMO optimal edge finish, much like angle, depends on properties of the steel and has a huge influence.

Good information nonetheless, just beware of the many factors that influence results.

 

[nozh2002]

Yes, comparing nozh's data to results of my own testing finds some radical discrepancies. I suspect different sharpening methods and edge geometry explain much ... I was surprised at the rapid loss of sharpness nozh measured with certain steels after only a few cuts. IMO optimal edge finish, much like angle, depends on properties of the steel and has a huge influence.

Good information nonetheless, just beware of the many factors that influence results.

Can you publish your results and test method you are using.

Thanks, Vassili.

 

[nozh2002]

One way to do this would be to present the results with and without geometry taken into consideration. Like a result "matrix". This way you can use your previous results (if you remember what grinds they were) and map them in a "total list" like the one you have, one "flat ground list" and one "hollow ground list". And maybe even a "22 deg" angle list and a "15 deg angle list". After that when you watch the different lists at the same time it would be fairly easy to predict the influence of grinds.

Different ways of presenting your data, without additional testing. Just a suggestion.
//Jerker

I think I already address this issue. Testing sharpness with thin thread where only very edge involved eliminates influence of all other geometry factors but angle - the very edge is same for all knives with 30 degree.

Thanks, Vassili.

 

[bullyson]

Vassili, why don`t you put to your test Bark River A-2 tool steel or Juka Hankala silver steel ? I know from my own little experience this is a hard process to be done that needs a lot of time and efforts. Therefore I must apologize in advance if my request looks impudent to you. I`ll be very oblidged to see how BRKT A - 2 will perform compared to the other current powder steels and especially Swamp Rat SRS 101.
Tnank you in advance.

 

[Dog of War]

Can you publish your results and test method you are

As my sharpening skills and methods have improved, my testing has become largely comparative so data accumulated over time would be hard to present in a useful fashion on the forums without tons of explanation. FWIW I started posting details of some of my edge retention testing over two years ago, for example this thread (only one I can locate without forum search privilege):

http://www.bladeforums.com/forums/showthread.php?t=424085

but interest seemed limited, so now just test for my own education, using fewer knives and comparing against blades I've used from test-to-test over time.

So, just speaking generally, two things strike me. First, I've found very few steels with sufficient edge stability to hold up really well with an edge geometry of only 30 degrees included, and many high alloy stainlesses need to be around 40 degrees to hold a fine edge. I suspect in your testing you're seeing what some have called a "self-sharpening" effect as the test progresses, this IMO is the one real advantage of steels with high carbide content as they tend to tear out and produce more "tooth". Of course this is only useful if you anticipate not being able to keep a blade near optimal sharpness, and that's never interested me much as it's not a problem I often face.

Second, edge finish and quality play a huge role, I've confirmed this examining edges under magnification. I generally finish with a microbevel at the desired angle using fine ceramic ... diamond media, including both DMT fine and extra fine grit do not leave nearly as clean an edge, and I believe this results in the edge being torn apart on media such as rope. Stropping on charged leather does not produce as good an edge as you get with ceramic, you really need a very fine, smooth, "hard" media like ceramic to produce the best edge. For high alloy stainless, I believe the ultra fine diamond stones would be worth a try. Thjen maybe follow by stropping on clay coated paper -- which BTW I've found works well on S110V.

------

Edit to add: if anyone happens to have (or can kindly find) the link to the thread I started in which this chart and related info was posted, I'd appreciate having it:

 

[nozh2002]

Can you tell what is those numbers on horisontal and vertical scales?

Thanks, Vassili.

 

[Dog of War]

Can you tell what is those numbers on horisontal and vertical scales?

Thanks, Vassili.

Sure ... in that testing, I was measuring edge retention cutting cardboard. Horizontal axis is total inches of cardboard cut (cutting was limited to a small section of each blade.) Vertical axis is sharpness as measured by the distance from point-of-hold that the blade would pushcut newsprint.

Again I hope somebody with forum search can find that thread, which I believe would have been posted here on or around 11/10/06; title of the thread was something regarding testing "early stage edge retention" if memory serves.

 

[nozh2002]

Sure ... in that testing, I was measuring edge retention cutting cardboard. Horizontal axis is total inches of cardboard cut (cutting was limited to a small section of each blade.) Vertical axis is sharpness as measured by the distance from point-of-hold that the blade would pushcut newsprint.

Again I hope somebody with forum search can find that thread, which I believe would have been posted here on or around 11/10/06; title of the thread was something regarding testing "early stage edge retention" if memory serves.

To measure sharpness you hold newspaper and see if edge will cut it on certain distance from holding point? Under what angle blade attack paper? How do you hold it.

Thanks, Vassili.

 

[Dog of War]

To measure sharpness you hold newspaper and see if edge will cut it on certain distance from holding point? Under what angle blade attack paper? How do you hold it.

Thanks, Vassili.

Correct. The blade is placed perpendicular to both the edge and the plane of the paper; no "attack" just rest is there and then see if it will begin to pushcut -- no draw/slice whatsoever -- with downward pressure before the tension of the paper is overcome. It is a surprisingly accurate, repeatable test with a little practice.

I'll email one of my friends who's a paying member here, see if he can find the thread which explains things in detail.

 

[nozh2002]

Correct. The blade is placed perpendicular to both the edge and the plane of the paper; no "attack" just rest is there and then see if it will begin to pushcut -- no draw/slice whatsoever -- with downward pressure before the tension of the paper is overcome. It is a surprisingly accurate, repeatable test with a little practice.

I'll email one of my friends who's a paying member here, see if he can find the thread which explains things in detail.

The way you hold it how do you hold it? It is not swinging free I guess. You actually measure this way pressure needed to start paper cut - this is what this distance transfers into ultimately. But it depends on how you fix it - how long fixation area in the top.

How many measurement you do at each point?

Thanks, Vassili.

 

[nozh2002]

I decided to retest at least first knife.

Reasons are:

1. I may get too good at testing (my hands shake less, I position blade better - something like this) so results became better and so I need to see what will be difference between very first results and current.

2. Nature of this test - dulling edge by cutting manila rope is random. I am very sure that results will be floating around. I did some repetitive testing when I cut threads to came up with this 21 cuts to measure sharpness, which is pretty stable. I think this is what I need to do as well for testing - it should be several testings (unfortunately it will take more then day) and median probably need to be taken as a result...

So I am retesting Yuna Hard II - ZDP-189.

Thanks, Vassili.

 

[thombrogan]

Edit to add: if anyone happens to have (or can kindly find) the link to the thread I started in which this chart and related info was posted, I'd appreciate having it:

http://www.bladeforums.com/forums/showthread.php?t=433156

 

[Dog of War]

http://www.bladeforums.com/forums/showthread.php?t=433156

You're the man, Thom! Many thanks for your help.

The way you hold it how do you hold it? It is not swinging free I guess. You actually measure this way pressure needed to start paper cut - this is what this distance transfers into ultimately. But it depends on how you fix it - how long fixation area in the top.

Not exactly sure what you're asking, but basically you just gently position the edge of the blade on the edge of the paper and slowly apply pressure ... and of course when you're several inches out from the point-of-hold, only very little pressure is possible since the paper will quickly roll/buckle/fold over. I've found that how long you try to get it to cut at a particular point doesn't make any difference ... you start out at a distance where you're pretty sure it won't be able to pushcut, and then gradually work your way closer to the point-of-hold. FWIW you get so you can tell when it's close to cutting, so it's pretty efficient. Note also that I hold the paper pinched between my thumbnail and index finger, which makes for a fairly precise point-of-hold; I experimented with holding the paper in a clip or clamp, but found it much more awkward, and that awkwardness led to less consistent results.

So distance from point-of-hold is a true gauge of sharpness. I didn't come up with this method BTW, a number of others use it or variations. IIRC Cliff Stamp at one time was running a challenge, people would send him blades they sharpened and he would record sharpness in this very way.

How many measurement you do at each point?

When I started doing this I simply would make as many cuts as I needed until I was pretty confident the distance was representative. But I soon found that the test is surprisingly accurate and repeatable, you can tell the occasional outlier rather easily. Anymore just two or three cuts is all I make, especially since as you continue through the test you're going to know if measurement at any one point was in error. So in that sense the method is sort of self-checking.

Couple comments on that old thread from 2 years ago: getting back to earlier comments, doing this kind of testing has had a huge effect on my sharpening skills, it's now typical for knives I sharpen to pushcut newsprint at 5" or more from point-of-hold. So this is why I say my accumulated data over time is all kind of relative, it's only by using some of the same blades from test-to-test that I have a basis for relative comparison. And of course many factors can lead to the same thing, including minor changes in sharpening media, angles and technique. But IMO this is still very useful, at least for our own, personal information.

 

[nozh2002]

What size of pieces of paper you are using and what brand of paper?

Thanks, Vassili.

 

[Dog of War]

What size of pieces of paper you are using and what brand of paper?

Thanks, Vassili.

Just newspaper newsprint, I'm sure it may vary in weight depending on the paper, what I've been using measures just over .003" thick. Cut into rectangles about 8.5" wide by 6" high (used to use smaller pieces but as my sharpening got better, well....) Make sure that the direction the paper tears straightest follows the width. You cut into the 8.5" side. During testing it's essential to trim off the edge after testing a blade's sharpness so the next measurement is valid; you can take the paper down to about 3.5"-4" high with no noticeable affect on the cutting measurement. Make sure the edge of the paper you're cutting into is trimmed very cleanly with sharp scissors for the most consistent results.

 

[nozh2002]

I decided to retest at least first knife.

Reasons are:

1. I may get too good at testing (my hands shake less, I position blade better - something like this) so results became better and so I need to see what will be difference between very first results and current.

2. Nature of this test - dulling edge by cutting manila rope is random. I am very sure that results will be floating around. I did some repetitive testing when I cut threads to came up with this 21 cuts to measure sharpness, which is pretty stable. I think this is what I need to do as well for testing - it should be several testings (unfortunately it will take more then day) and median probably need to be taken as a result...

So I am retesting Yuna Hard II - ZDP-189.

Thanks, Vassili.

I just finished retest:

Yuna Hard II ZDP-189 (10 Oct 2008, 1 Dec 2008)

CUT
000 010 010
001 015 015
003 025 020
006 040 020
010 040 030
015 040 025
020 055 030
030 055 030
040 055 040
060 055 050
080 050 045
100 055 050
150 065 045
200 080 050

Results are different, so somehow I adopted to testing and start doing it better - one way or another - this need to be analyzed. Is it way I test sharpness, or the way I cut rope - I do not know. But this adoptation need to be somehow accounted. So I can not directly compare old and new results. I guess it should not be much difference in results of the tests done at same time, but defenetly I can not compare recent test with month and a half old.

I think I need to test Yuna Hard II few more times and then analyze what I will get. Or may be I should retest Sandvic and then Yuna again - having them be retested several times and see what results will look like.

Thanks, Vassili.

 

[theonew]

I just finished retest:

I'm glad you finally did a retest. I assumed the results would be a little different, but yikes, that difference looks greater than between similar steels even

 

[nozh2002]

I'm glad you finally did a retest. I assumed the results would be a little different, but yikes, that difference looks greater than between similar steels even

This is expected - Yuna Hard II was first knife I tested in almost two months ago, now I am adopted to this and start getting better and better results. So I decide to retest to see if results for same steel will be better now then i was when I just started. Please notice that results are better not worse, so it is not some random variations but exactly adaptation.

Question is did I stop adopting or in time I will start getting excellent results for any steel, when this adaptation stopped, from what point results are same as they are now?

Anyway it is clear that I need to retest more.

Thanks, Vassili.