Edge Sharpness Tester

[ToddS]

Can you guys make out that ring-like artifact that is formed just shy of the outer edge of the media? In some instances it disrupts the striations, interrupting the straightness of the lines, other times it is actually protruded, and others seems sunken beneath the surface. In fact in some of the instances it seems like it's almost been stretched out.

It appears that both the BESS media and Josh's fishing line have an outer shell. I suspect the fishing line shell provides more secure knotting.
It looks like the stropped edge cuts most of the way through then the last bit stretches and breaks.

The striations in the coarse-honed blade result from cutting (smooth) in the sharp areas of the blade and ripping/stretching (rough) along the path of the dull areas of the blade.

 

[KennyB]

It appears that both the BESS media and Josh's fishing line have an outer shell. I suspect the fishing line shell provides more secure knotting.
It looks like the stropped edge cuts most of the way through then the last bit stretches and breaks.

The striations in the coarse-honed blade result from cutting (smooth) in the sharp areas of the blade and ripping/stretching (rough) along the path of the dull areas of the blade.

I see. Must be some kind of case hardening or something.

One thing I'm not sure about is the direction of those cuts... Hard for me to tell where the cut starts or not but I think the theory of high/low spots in the apex severing the test media more readily.

If you think about it, the finely honed edge might be like what, 1 um at the apex? The width of the apex on the coarse edge may be wider, however it might also have highs and "peaks" on the edge that are smaller than 1 um in width and/or diameter.

 

[ToddS]

I see. Must be some kind of case hardening or something.

One thing I'm not sure about is the direction of those cuts... Hard for me to tell where the cut starts or not but I think the theory of high/low spots in the apex severing the test media more readily.

If you think about it, the finely honed edge might be like what, 1 um at the apex? The width of the apex on the coarse edge may be wider, however it might also have highs and "peaks" on the edge that are smaller than 1 um in width and/or diameter.

I believe these media are extruded with two different polymers. I am wondering if the outer material in the fishing line contains particles to provide grip for knotting - this may explain the variation in the measurement.

The width of the two blades will be very similar, less than 0.1 micron apex width. The difference will be that the stropped blade is nearly continuous with only occasional micro-chips - those chips cause the striations in the media. The coarse edge will have many chips of varying size, and the width of the apex at the base of those valleys/chips will be on the order of 1 micron - the wider those valleys/chips, the wider the "ripped" striation in the media.

 

[HwangJino]

I mainly cut cardboard boxes at work, sometimes thick plastic bags that contain fish, the vacuum sealed stuff.

No factory knife cuts cardboard well, it will snag and leave a messy cut.

I will sharpen with the spine almost on the stone (wide bevel), then slow convex to about 10 DPS.

It flies though cardboard at any angle, and any cardboard.
Sometimes I get the wax cardboard (meant to carry 30 to 40 pounds of veggies). Flies through that too.



If my blade drags, I'll repolish.

All my sebenzas had the bevel widened and polished.

It will still cut rolled wax paper, which is difficult.

 

[chiral.grolim]

The fishing line shows similar features; the lines get deeper as the cut progresses, presumably due to stretching of the material due to wedging of the blade.

... that ring-like artifact that is formed just shy of the outer edge of the media ... in some of the instances it seems like it's almost been stretched out.

... Hard for me to tell where the cut starts or not ...

Found this thread from a link on Jim's BESS thread, my apologies for bumping it, but I was wondering if the "direction of cut" was ever established.
Regarding the photo above, I would have guessed that it started on the right where there are clear gouges in the media. However, the depth of the cut as evinced by the gouging is <40 um, the perfect form of the central mass indicates it never touched edge/apex but simply split away from wedging and tension until it stretched & snapped with the deformation on the left. Is that what others are seeing? Is that what HH was referring to as the "snap-zone"?

In the image of media cut by the 200 grit-edge, there is apparent (and irregular) gouging on the left and a stretched shell on the right, ToddS focused on the gouging.
In the image of media cut by the .25 diamond-paste stropped edge, there is hardly any apparent gouging on the right, it is VERY clean, and again a stretched shell on the left.

How much of BESS is penetration-force (actual cutting) and how much is wedging force (just pushing the media apart along a natural path ahead of the apex)?

 

[ToddS]

Found this thread from a link on Jim's BESS thread, my apologies for bumping it, but I was wondering if the "direction of cut" was ever established.
Regarding the photo above, I would have guessed that it started on the right where there are clear gouges in the media. However, the depth of the cut as evinced by the gouging is <40 um, the perfect form of the central mass indicates it never touched edge/apex but simply split away from wedging and tension until it stretched & snapped with the deformation on the left. Is that what others are seeing? Is that what HH was referring to as the "snap-zone"?

In the image of media cut by the 200 grit-edge, there is apparent (and irregular) gouging on the left and a stretched shell on the right, ToddS focused on the gouging.
In the image of media cut by the .25 diamond-paste stropped edge, there is hardly any apparent gouging on the right, it is VERY clean, and again a stretched shell on the left.

How much of BESS is penetration-force (actual cutting) and how much is wedging force (just pushing the media apart along a natural path ahead of the apex)?

Josh did not mark the "top" but I would guess this (stropped) was cut from right to left.

I had the same question about cutting vs wedging when I asked if anyone would try measuring a blade before and after gently muting the edge. We are still waiting for someone to volunteer to perform those measurements, so your bump is appreciated.

 

[HeavyHanded]

I believe the accepted interpretation is that the material was severed in the entire region where there's evidence of grind scratches etched into the surface. It appears to start on the right, with heaviest evidence of scratch marks and debris pushed into the cut, as it approaches the left side the material reaches its failure point and snaps - no more evidence of cutting and distortion from pulling apart.

The coarse edge appeared to undercut the outer shell, the finer edge appeared to overcut the outer shell. I suspect if we examined both halves of both cuts we'd see the material doesn't cut dead perpendicular when the cut initiates and one half will be under, the other half will be over. The undercut half might always look like it took the brunt of the initial damage.

The snap zone also looks reasonably consistent across images to me, again, it would be nice to see both halves.

Edit to add:
I believe any intentional dulling of the edge will have drastic effect on how the material is severed, to the point where it would completely change the morphology. Someone with a guided system might have luck using the same finish and slowly broadening the angle.

 

[HeavyHanded]

I'll add to the above this speculation. If there was any significant wedging action - the material splitting ahead of the edge - we might not expect any burst zone at all, it should split right through to the other side. Visually the outer layer shows signs of being swept in the direction of the cut, otherwise it shows grind pattern passage much as the core. The burst zone appears to encompass both outer layer and inner core.

Presumably if we loaded it up on a 100% dull edge the entire cord would show burst damage. Possibly one can determine as the edge becomes more able to cut the cord, the burst zone will shrink. Might be a correlation between the area of the burst zone and BESS number, but then this should also be reflected in the acuteness and/or finish level of the edge. The burst comes after the initial penetration and the BESS number is already established. As an added consideration, higher BESS number automatically means more pulling force on the cord once it begins to separate.

edit to add:
The entire action is not understood IMHO. We know dwell time influences BESS score, maybe the cord does not cut in an instant, only the burst zone does. Still I see no evidence of wedging ahead of the blade, there must still be some wedging/compressing of the material or the scratch pattern depth would be uniform end to end and it isn't.

 

[ToddS]

The striations are not scratches, but areas where the media is stretched/ripped rather than cleanly cut. These would correspond to microchips in the blade. The polished blade, which cuts much more cleanly, leaves very few of these striations. I believe these striations are "smoothed out" by the bevel burnishing them as it passes, also the wedge-pressure will be highest near the start of the cut where the thickest cross-section of the bevel is in contact.

In the polished blade cut, there are clear lines of hesitation perpendicular to the direction of cut - this suggests to me that wedging is limiting the progression of the blade through the media. All of the media cross-sections I looked at had the same rip/tear/burst ending over the last 30 microns or so.

 

[HeavyHanded]

I dunno...

Some of the striations show evidence of being pulled apart, many do not and IMHO could very easily be a record of the passage of lateral variations in the edge. On areas where there are greater variation in the lateral and profile of the edge, you'd expect the lower trailing regions to tear the material, the higher leading regions to make the cut, depending on the compressive forces at work.

The hesitation lines to me appear to be evidence of compression prior to the material being cut again - as the edge progresses, the material back from the active cutting region is going to compress. This artifact might also be the release of that compression, revealed as the material expanded while the edge was advancing. Is entirely possible all the compressive force was from the initial load, and not a progressive loading/releasing.

To me the biggest indication that wedge splitting is probably not much of a factor is how clean the break point is on the fine sample. The demarcation line is very clear and to me appears to be cutting clean till the material failed.

 

[BluntCut MetalWorks]

I think, this stiff test thread was about 20* clock-wise torqued/twisted. Studdering striations(accelerate then decelerate) lines caused by un-even wedging and steering by bevel scratch/gouge lines. Entrance wedge-cut direction and exit fractured (upper left) tell tales supporting my assertion.

 

[Jason B.]

I will preface this by saying, my opinion is strong but accurate, if this device is your holy grail that's fine but do not respond to what I say with emotion or in defense of the test unit. These are my opinions.

I have refrained from making comments because I think, after much use, that this machine is not much more than a gimmick. To me, it's like one of those carbide pull through sharpeners, it works but it's not very accurate or consistent and has a number of design flaws that promote human error. From the method of adding weight to the test material or the BESS scale which seems to be too narrow to actually measure sharpness, I just can't see how this unit in its current construction will do anything but confuse the user.

Now, I would like to think that my sharpening skill is just that good but when you average 32 grams on machine sharpened edges and down to 5 grams with hand sharpened edges you get a feeling the BESS scale is not proportionate to edge sharpness. I've also discovered that a polished coarse edge, be it from a machine or a coarse stone and strop will "trick" the media and create very low numbers (20-40 grams).

I think having the DE blade as a Zero measurement is misleading, the sharpness of a razor is much greater than my machine edge or one of my 2000 grit waterstones yet they read within just a few grams of that goal. It was fun to experience this test unit but in the end I feel it needs a greater level of technical input on the design end.

 

[ToddS]

I think, this stiff test thread was about 20* clock-wise torqued/twisted. Studdering striations(accelerate then decelerate) lines caused by un-even wedging and steering by bevel scratch/gouge lines. Entrance wedge-cut direction and exit fractured (upper left) tell tales supporting my assertion.

That is a good point - I had noticed this effect on several of the severed media, but it did not occur to me that it was due to torsion in the media being released as the cut progressed.

I dunno...

Some of the striations show evidence of being pulled apart, many do not and IMHO could very easily be a record of the passage of lateral variations in the edge. On areas where there are greater variation in the lateral and profile of the edge, you'd expect the lower trailing regions to tear the material, the higher leading regions to make the cut, depending on the compressive forces at work.

The hesitation lines to me appear to be evidence of compression prior to the material being cut again - as the edge progresses, the material back from the active cutting region is going to compress. This artifact might also be the release of that compression, revealed as the material expanded while the edge was advancing. Is entirely possible all the compressive force was from the initial load, and not a progressive loading/releasing.

To me the biggest indication that wedge splitting is probably not much of a factor is how clean the break point is on the fine sample. The demarcation line is very clear and to me appears to be cutting clean till the material failed.

Sorry, I was not clear, I do not mean wedge splitting, but rather friction between the bevel and the partially severed media related to wedging/compression.

Here are a few more images...

... I've also discovered that a polished coarse edge, be it from a machine or a coarse stone and strop will "trick" the media and create very low numbers (20-40 grams).

...

I wouldn't call that a "trick" but rather preparing a blade which performs this particular test well - the polished apex for optimal push-cutting and the scratched bevel to minimize contact area and therefore stiction of the bevel with the media.