Sharpening with different grits on opposite sides of the edge

[chalby]

"There is no bigger eye-opener than a good 20X loupe on a freshly sharpened blade." (c) not me

Microserration created by asymmetrical sharpening has two applications: scalpels and rope cutting competitions. Microserration wins competitions because of the cutting performance, not the edge retention that is very bad. People who studied the topic gave up after their first injuries. Hacksaw profile micro-serrator IS traumatic. Good for scalpels only.

Why though? What makes it good for scalpels? Why does this method seem to give considerably longer edge retention cutting rope? I would think rope would be not dissimilar to other common materials that we use a knife on in EDC.

I don't know either way. There are a lot of variables just in this particular set of tests, not least of which is the differences in sharpening method and skill. Just saying something is so doesn't add weight to the debate.

At least give the guy credit for trying something outside the square, even if it doesn't quite work the way he is thinking.

 

[ToddS]

Nobody is questioning the existence of micro-serrated blades. However, they aren't created with stones, and they don't slice paper very well - certainly not as was shown in the video.

 

[HeavyHanded]

My understanding is that scalpels are sharpened the way they are to speed up production time. A somewhat rougher edge creates a cut that mends faster and an edge that has more purchase on tissue. The polished side has virtually no grind pattern (of the ones I've seen). This method yields a more consistent product compared to finishing both sides.

Here's a few older pics taken at 1000x, 800 grit, 45° to the viewing angle. The first is fresh off of 800 wet/dry, second is after being stropped/burnished on plain paper. Small red bar upper left that is missing from the second pic (smaller than the text) is 3.4 micron - width of entire image area approx 80-85 micron. Resolution isn't strong enough to tell if the apex is fractured in the first pic, less likely in the second. Steel is Buck 420HC

 

[Craig James]

ToddS ,

Been meaning to say for a while that I’ve been impressed with the quality of your microscopy. Back when I was doing my phd I spent a lot of time locked in my university’s electron microscopy suite on sem, tem and fib/sem and fully understand the amount of time it takes to not just image but also prep the samples appropriately. Some of the images you provide with comparisons on the same area after different treatments must have been a royal PITA to get right.

Do you do this as a consequence of academic research? Great job as always

 

[wdtorque]

Scalpels only? So, I'd guess it would be good for fixed blade broadheads? (serious question)

 

[c7m2p3]

This could be very interesting. Looking forward to Pete doing some more testing on his own since there are a lot of variables in play here. It is possible that the person that sharpened this blade for him is just a really good sharpener with years of experience and thus the edge that he is putting on there regardless of technique or grit is going to outperform what pete or the average sharpener is able to achieve with a Tormek, KME, or Worksharp. If this is true, it would be a great way to throw an edge on harder use blades.

 

[PaultheCarpenter]

Merge

 

[ktataragasi]

I just watched his videos over the last couple of days and it does seem rather interesting. But I think this also comes down to having the proper edge for what you are cutting.

I think sharpening every edge to the same finish and degree is great for benchmarking something that has so many variables but it doesn't really mean each blade steel is optimized at that angle and polish. Some people love using a course stone only to sharpen on and others will polish the edge no matter what.

Maybe this edge is a best of both worlds or a compromise of both that just lends itself to decent results.

 

[PaultheCarpenter]

I'm leaning toward the best of both worlds, but only time will tell. I can say that I have never had such a scary sharp edge from such little work.

 

[HeavyHanded]

Couple of thoughts on this:

- I use a maybe similar strategy by applying as low as 80 grit edge with an 8k microbevel - enough to thin and clean up the apex but not enough to eliminate much of the along edge variability. I get very good longevity with this approach.

- The application of the finer abrasive is going to erode the high points on the 250 grit side no matter how carefully you do it. Any testing should be measured against a rough average 'control' edge prep'd to a midpoint between the two edge finishes. Disclaimer - that is exactly what I did years ago playing around with this same approach and I found no functional difference between the two.

- Another avenue for testing (not applicable to high carbide steels) would be to lay in a coarse edge and use a smooth steel or glass on only one side. This will preserve more of the coarse edge morphology.



Previous discussion:
https://www.bladeforums.com/threads/polished-on-one-side-coarse-on-the-other.1724748/

https://www.bladeforums.com/threads...being-updated-occasionally-july-2020.1450834/

 

[scottc3]

I tried.. it's a slider, low and inside, 93mph, it's a swing and a miss, retiring the side, bottom half Giant's up 3 zip...
Konstantin, apropos

Microserration created by asymmetrical sharpening has two applications: scalpels and rope cutting competitions.

I'm led to resharpen my BM810 toothy then asymmetrical, but I'm guessing it will be my kid's or grand kid's that discover the difference in the M390, because I'll be dead by then. Because I still have not resharpened my 940-1501, two years later, a swipe on the hone, strop on the pants and Benchmade's 20cv is ready to go again. No longer a super low drag Ninja am I.

 

[scottc3]

Sorry, allow me to be clear, never I was.

 

[scottc3]

micro-serrated blades... aren't created with stones

Technically accurate statement, seriously nice image. Although Gab uses "nano-serrations", maybe we need another word for toothy edge production technique? The first SEM reminded me of wing vortex generators, cutting a different medium, "perpendicular." Surely a lot of coin has been spent investigating serrations to solve very specific cutting tasks.
I'll never forget hearing Sal say serrations give more cutting surface per blade inch. That observation was a smack the forehead moment for me. The original full serration Salt in H1 design can cut rope.
I stayed away from serrations until then because I thought serrations were hard to sharpen. Moving forward, I started playing. Bread knives-full serrations, a Grip-partial, and s30v sharpened to 600 grit or so. I'm even flattening my Venev 1st gen bonded diamonds using extra course SIC to get more "tooth" off stones. For me, at the moment toothy edges are great. Hearing and reading practical experiences with theories in mind, here's my workflow, all trailing edge:

Flatten Benchmade 940 20cv edge with KME 50 grit "beast." (My 940 is 2.33 ounces, always easy to carry).
Sharpen one side with 150 grit ~90μ Venev 1st gen, at XX degree angle until burr forms across entire blade.
Strop 150 grit side with 1μ white impregnated Levis, inspect until burr is removed.
"Burnish" the second side with Gritomatc's 2500 SIC ~2.5μ. (my thinking would lead me to use 1200grit ~2.5μ 1st gen Venev bonded diamonds). Closest I own to Gab's 3μ.

UP TO A RIGHT ANGLE, approaching but not intersecting apex? How far apart? Gab's comment is unclear "sharpens the other side at a perpendicular angle to the first side at a much higher grit"). Thinking of all the boundary SEMs Ive seen, the width on this mountain top flat bridging towards the first bevel may be where rope cut counts increase in number for steel and geometry of Gabs 2 knives.​

Strop 2.5μ side with 1μ white impregnated Levis as directed by Gab.
Test for sharpness using paper slicing twice a year.​

 

[FortyTwoBlades]

Part of the reason why serrations function well on fibrous materials is because of the angle of presentation of the edge, as well. The points of the teeth sinking into the fibers to initiate the cut prevents initial glancing and then the very square-on chisel-like presentation of the interior serration edge traps and severs the fibers in sequence. A similar effect happens with coarse edges.

 

[Gritomatic]

Nobody is questioning the existence of micro-serrated blades. However, they aren't created with stones, and they don't slice paper very well - certainly not as was shown in the video.

As far as I know, the origin of micro-serrated knives is Romani gypsy horse stealers. The purpose of knives (cutting parts of the harness) dictated "cut or die". Make a blade capable to cut with a single swing for whatever it takes, or be hanged. By the way, when people read about "different grits on opposite sides", they imagine normal progression from coarse to fine with the early finish for one side. This is oversimplified. In gypsy sharpening, a coarse stone is used AFTER the full progression is done.

Scalpels only? So, I'd guess it would be good for fixed blade broadheads? (serious question)

Maybe strap cutters for parachute-jumper and divers. The same problem - "cut or die".

 

[FortyTwoBlades]

Uh...what?

 

[Mr.Wizard]

In gypsy sharpening, a coarse stone is used AFTER the full progression is done.

Clay Allison of Wicked Edge used to have a page and video where he did that, but it's gone and the Internet Archive copy of the page just shows a spinner. All that remains is the image below. I cannot recall if he did this only for appearance or claimed a performance advantage.

 

[Mr.Wizard]

Here is Maxamet sharpened with Wicked Edge 600 grit diamonds. This is very typical of 'non-linear' edges, where the high spots are mostly burrs and the low spots are mostly chips.

That edge is much less keen that one given by the DMT 325 as you showed in The Diamond Plate Progression, below. Why is that?

 

[DeadboxHero]

Beautiful images

Here is Maxamet sharpened with Wicked Edge 600 grit diamonds. This is very typical of 'non-linear' edges, where the high spots are mostly burrs and the low spots are mostly chips.
If you hunt, you might occasionally find a feature that looks like a serration, but it's just not typical in most situations. First problem is that the grit just doesn't penetrate that far, second problem is that most of these "scratches" are burnishing lines, not grinding lines.
As HeavyHanded pointed out, you need a very small number of abrasives, like a single row (think cheese grater) to get sufficient penetration to make something simulating a serrated edge. Softer steel would help too.

 

[ToddS]

That edge is much less keen that one given by the DMT 325 as you showed in The Diamond Plate Progression, below. Why is that?

The DMT edge is on a straight razor, so much larger contact area and therfore lower pressure. Essentially the pressure is too low to cause abrasion, only burnishing. The 600 grit is a Wicked Edge paddle on a curved blade, so much smaller contact and therefore much higher pressure (even with light strokes). This is one of the reasons that it's a waste of time to use sub-3k grit stones on razors.