Microserrations

[Thomas J Ekman]

I have found out that for the mediums I cut, like boxes, envelopes etc, leaving an edge that is not completely polished, but finished by a sharpening steel produces an edge with more "bite" than if I continue the process with a leather strop.
Is this because leaving some microserrations makes the edge act as having a regular serration in miniature or what?

 

[wolfmann601]

I cannot answer this like Cliff Stamp would, but I think I know what you are saying. I too have some knives that I sharpened with a "toothy edge". Matter of fact, when I cut cardboard, tiny specks would remain on the edge and I would "pick" the specks of paper off. I found a polished edge seemed to cut better though.............wolf

 

[Elwin]

This is just IMHO, but I have found a more polished edge to cut better. Some will no doubt disagree. Zipper cuts work better for me on cardboard. I typically dont cut much rope, but the one time that comes to memory was a polished Bear damascus balisong cutting a slack poly rope used as a yellow safety marker. Now, to contradict myself, the microserrated edge yielded by a coarser final honing feels sharper when I use my thumb to test the edge. I have no doubt that microserrated edges work, similar to the "serrations in miniature" you mention, I just prefer to polish the edge.

"Is this because leaving some microserrations makes the edge act as having a regular serration in miniature or what?"

I think that is correct, but really have no theory to back it up.

 

[Joe Talmadge]

If you're slicing, a coarser edge will definitely work better than a polished edge. On the hard poly rope I normally use as a sharpness tester, a polished edge will normally just skitter across the top, barely cutting at all. A coarse edge will bite deeply. The difference in performance is not small, it is huge, but obviously this depends on the material being cut. Hard poly rope seems to bring out the extremes in performance between polished and coarse.

On softer rope, there's a different proposition that is interesting. Coarse-ground will still outslice polished. But if you take a blade and really thin it out, and then polish it up, you might be able to pushcut through soft rope -- and pushcutting is the easiest. So coarse-edge endura beats polished-edge endura, but super-thin super-polished Calypso jr. beats 'em both, because I can do a pure push-cut with the Calypso Jr.

So ultimately, the performance you see depends on the mixture of slicing and push-cutting you'll have to use. The more you can push-cut, the more carefully you'll have to adjust the grit. For something you can't possibly push-cut through, like that hard poly, coarse wins and wins big.

So, do the coarse grind act like serrations? Well certainly, it feels somewhat like serrations. Serrations often consist of a somewhat-polished edge, arranged in arcs, and the cutting is enhanced by the geometry. When I look at a coarse edge closely, it is a bunch of big scratches, and a final edge that's less consistent, with more waves and inconsistencies than in a polished edge. That does help to change the geometry as it cuts.
Differences between serrations and coarse-ground edges? Well, serrations tend to keep their cutting effectiveness longer than a plain edge of any type. By contrast, a coarse edge will lose its effectiveness faster than a plain edge, in my experience. Serrations are little polished edge arcs, protected by and enhanced by the "points". Coarse-ground edges are uniformly-coarse inconsistencies that can act like serrations sometimes, but don't have the "protective" effect of a purpose-built serrated geometry.



Joe

 

[Cliff Stamp]

As Joe noted, the type of edge that is optimal depends on if you are push cutting or slicing. However while the optimal edge for push cuts is the very highest polish possible, the optimum edge for slicing is not always the most coarse finish that you can apply. A coarse finish acts just like a saw, and thus there is a maximum amount of "hunger" that is practical. Now you might say just make it as hungry as possible so it cuts with the maximum depth per stroke. However the more hungry a saw, the more difficult it becomes to pull/push it through the material. In general you want the most coarse finish which allows a practical amount of force on the pull/push. This depends both on the medium being cut and the person doing the cutting. In general the more stiffer the medium and stronger the user, the more coarse the finish they will find optimal.

Serrations often consist of a somewhat-polished edge, arranged in arcs, and the cutting is enhanced by the geometry.

I think Steve Harvey hit upon a very critical point in regards to serrations in that one of the main reasons that they cut better than plain edges is that they are ground much more acute, often by a factor of 2-3. As well, the serrations that I have checked recently under magnification are very rough (Mission, SOG), I don't think they are polished at all, just ground, this also greatly enhances the edge life for slicing. The changing of cutting angles argument isn't really the dominant effect.

Serrations are little polished edge arcs, protected by and enhanced by the "points". Coarse-ground edges are uniformly-coarse inconsistencies that can act like serrations sometimes, but don't have the "protective" effect of a purpose-built serrated geometry.

I thought the same for quite some time, and in fact this is true up until a point. Basically in order for the micro-teeth to have the protective nature of a serration pattern they have to be of a decent size. For example I recently reprofiled a SOG SEAL 2000 on a 100 grit AO belt (primary and secondary grind). After I was finished altering the geometry I checked the edge under magnification and found that the teeth were up to 0.15 mm deep and up to 0.25 mm long. These teeth were large enough to actually have teeth inside them. I cleaned up the edge by stropping on canvax loaded with wax. This removed the debris and did a slight aligning, the blade would now shave evenly on both sides, but was rough.

I did an edge retention test by slicing 3/8" hemp through 2" of blade length, to check how the blade cut, and how the edge held up to extended use. Sharpness was tested by standard means I have described before (thread, poly, and on the hemp itself). The blade started out by cutting the hemp with between 11-13 lbs. After 510 slices the performance had degraded to between 19-21 lbs. I then did 150 slices through dirty 5/16" poly, which was actually leaving dust on the cutting block. The blade had then degraded to 25-27 lbs on the 3/8" hemp. After five alternate strokes on a smooth steel the performance jumped back to 17-19 lbs and was stable through 14 further test cuts through the 3/8" hemp.

Throughout the cutting I was checking the edge degredation under 20x magnification. I found that just like a serration pattern, these large micro-teeth would first wear along the tops, and thus the inner scallops were protected from abrasion for an extended period of time. The deeper the teeth, the more protection as the more material has to be worn away (or deformed) for the edge to stop cutting, thus the more coarse the finish the longer it lasts and the more protection from really gritty materials.

If you try similar work with a coarse edge that is much finer, say 600 DMT, you will not see the same level of edge retention. The teeth formed by the 600 grit DMT are much smaller, around 0.035 +/- 0.05 mm in depth, just visible under 20x magnification. While this finish has much better slicing ability than a high polish, and much better edge retention during such work, it wears down much faster than the x-coarse belt finish, and does not have the protective nature of the much larger teeth.

I am going to get some coarser belts and see how they work, a 40 grit should produce micro-teeth that are just barely visible and bump the slicing performance up another level.

Serrations however do retain a number of advantages of such coarse ground plain edges, primarily you can do really abusive cutting to a serration pattern like slice on a ceramic plate. Because the point on the serration pattern are so much thicker than those on the micro-teeth, they will protect the scallops whereas the microteeth will all get squashed. The microteeth finish however is trivial to sharpen, the serrations are not.

-Cliff

 

[Thomas J Ekman]

So the bottom line is that the micro serrations obtained through a steel will not last long, is that what you are saying?

 

[Larus]

I sharpen most of my everyday kitchen knives with a diamond rod. That is pretty course and slices very well. Also, since the edge must meet with wood, glass, or plastic boards, there is not much sense in spending a lot of time sharpening. I sharpen each knife after each use while it is washed.

For outside the kitchen, I have found that the 800 grit stone provides the best edge. There is enough bite to slice, but it is polished enough for edge retention. You may prefer 1000 or 1200, but do not get too fine for general purpose blades.

Chisels and plane knives get honed all the way up to my 8000 grit water stone. (Which never sees water. I use WD-40 for all my water stones). The highly polished edge is required for push cutting. Anything less results in too much hard work using the tool and the edge does not hold if course honed. I will stop with the 6000 grit stone if I am in a hurry.

I really do not like the polished edge for general purpose cutting. It seems like a lot of work that results in inferior cutting. The edge does hold longer, however.

 

[Bart student]

For those of you with a grinder, take a look at the edge you get by making the final bevel with a 320 (euro-grit sizes) belt and polish this edge lightly to remove the burr, yes, with a buffer wheel and fine polishing paste.
You can't remove the scratches made by 320 grit this way, they're too big. BUT .. you do polish whatever is inbetween those scratches ... if you take a microscope and look at 300 x times ... awsome... looks a bit like spyderco serrations only VERY small.. and guess what. it shaves like a dream, yet keeps a grabby edge that really bites - basically it just grabs like you would from a papercut.

you know.. those wounds you notice when blood is at your elbow from cutting your pinky, and when you look at the cut for three seconds, it starts to hurt like hell

greetz and take care.

 

[Cliff Stamp]

Thomas:

... micro serrations obtained through a steel will not last long

In general, the more coarse the finish, the better it will perform slicing, and the longer the edge will last. Of course, the opposite is seen with push cutting. The more coarse the finish, the worse it will perform push cutting and the faster it will degrade.

Joe came up with an excellent yet simple solution to this problem. After doing the prelim sharpening with an x-coarse hone, you only polish part of the blade. This means you have a section left very coarse for slicing, and another left very polished for push cuts.

-Cliff

 

[wolfmann601]

 

[Keith Montgomery]

I find that microserrations are a great advantage in the type of cutting that I do. I never highly polish an edge. I use a medium stone and then a fine stone and then sometimes a couple of swipes on a strop with green polishing compound.

 

[Jeff Clark]

This discussion has drifted over to emphasize edge durability rather than cutting efficiency. While a moderately toothy edge may not last as long as a highly smooth or highly coarse edge it is easy to maintain. Meat cutters for years have settled on maintaining their relatively soft blades with a steel. If you are not going into the woods for a long time without a sharpener you may find a steeled edge your most efficient utility edge.

I usually sharpen to a smooth edge then go back and make the edge a little coarser. I do most of my work with about a 600 grit diamond hone. Then I use ceramic rods and/or strops to get a fine burr-free edge. Then a few light strokes of 600 grit again to get tooth. Periodically I use a steel or a couple light strokes on the 600 grit. I don't spend much time to maintain an optimal edge.

 

[darkman]

the steel puts a micro-serration on the blade...
just like t-rex teeth..they have it down the dorsal ridge of the
tooth..it cuts flesh like a chainsaw...
what you need is a knife with a blade out of CAST DENDRETIC STEEL..
ITS MOLECULAR ARRANGMENT PUTS A MICRO SERRATION EDGE TO THE BLADE
WHEN SHARPENED...if you want one..let me know..be glad to make you
one...dm

 

[Cliff Stamp]

Jeff Clark :

While a moderately toothy edge may not last as long as a highly smooth or highly coarse edge it is easy to maintain.

Yes, another consideration is the speed at which very coarse edges will grind away a knife. With a very coarse abrasive, each sharpening can remove 0.5 mm of metal easily, this adds up quite quickly. This is how I have been sharpening all cheap knives lately, personal use and friends. It gives a high slicing performance that lasts the longest, and who cares if it wears out the blade.

However on high end customs this is not really the way to go. On them I usually finish with 1200 grit DMT. On such knives the geometry should be significantly better and thus you should not need an extremely coarse a finish anyway, if this isn't the case, then you are buying the wrong customs, assuming you are performance driven of course.

In regards to a grooved steel, it acts like a file on blades soft enough, and thus leaves a very aggressive edge.

-Cliff