Coarse edge = Micro serrations yes or no

[GRIM 62]

Like in real serrations(Spyderco),no.

 

[HeavyHanded]

I reviewed the last few paragraphs. Re read it (I did not change anything) realize that "micro serrations" and serrations are being used in that discussion to discuss 2 very different things. Replace "micro serrations" with "coarse edge" if you like, and see if you follow.

Basically I am saying that the medical industry does not use Coarse edges or "micro serrations" because a polished edge disrupts the tissue less and heals faster. Serrated edges (true serrated edges) are also not used because the DO disrupt tissue more than a plain edge, but I am suggesting that they do NOT disrupt tissue on the scale that a coarse finish will (once scaled up to a similar dimension of edge relief). By "edge relief" I mean the irregularity owing to the tips of the teeth and the depth of the troughs in between.

If you then take the coarse edge and scale it up to a dimension similar to the dimension of a serrated edge (where the " teeth" are a few mm tall) and make a cut it will shred whatever you are cutting...by contrast a true serrated knife will not shred the media to a similar degree.

Does that help explain the idea? I freely admit it is difficult to represent this with words. I welcome the questions, but I hope we can keep them constructive instead of argumentative.

I imagine there are plenty of other considerations for why the medical industry uses a finely polished edge over a relatively coarser one, not the least of which is that it's very difficult to produce a clean, coarse edge with a blade that's less than half a mm thick. That said there have been quite a few discussions about coarse vs fine regarding wound healing, and the general consensus is that a cut from a coarse edge heals much faster all other things being equal. A fine cut leaves a much smaller scar, particularly when sutures are involved. I tried to find a reference to what level of refinement a scalpel is ground to, suspect its way up the scale but haven't one to examine.

As far as scaling up a coarse edge goes, I imagine the edge would look more like a piece of sharpened corrugated roofing, or like the edges found on some grass whips. A (crosscut) saw edge is actually a series of fine edges in series that remove material by a process of shaving out small (or not so small) pieces, like a row of chisels. A coarse edge (and fine edge that hasn't been polished smooth) by contrast, cuts using a number of factors. There's the shoulders of each spot where a grit has cut a scallop out of the edge. These are going to look (blown up) like a traditional serrated edge, which does most of its cutting using the upper portion of each cut-out's trailing edge and does resemble the action of a saw (assuming a certain amount of draw to the cutting stroke, there is some debris generated - at least when cutting hard materials). Most of the cutting surface on a ground edge is a combination of places where abrasive grits have overlayed each other, and where they've matched up to varying degrees on opposite sides of the bevel. Looking straight down at the edge you'll see how it weaves back and forth over the total width of the cutting edge, with the majority of the bevel meeting up very well. This produces an edge that slices through material with a constant (if very slight) shifting of cutting force, not with a series of chipouts. I guess if one were to sharpen an edge at an extremely large grit and not strop it, you'd have all manner of trailing metal debris that would fall off very quickly, but that would be akin to leaving a large burr on a more finely polished edge - it would be a poor example of the species.

I once used a chain saw bit for a dremel on a thick bladed knife - applied it all on the same angle and more or less randomly cut into both sides of the edge, some a little deeper, some a little more shallow, simulating consistent passes on a monster-sized stone. You can do the same test with any thin piece of metal, a round file, and some patience. An even faster model can be constructed using a piece of hardwood and a rasp. It rapidly becomes apparent just looking at the thing, that there are a number of factors involved when an edge is cutting, particularly when the edge is being drawn across a material. FWIW, I EDU'd this knife for a month or so and it was a terror on tougher materials. I was partsing out a large piece of equipment at work during that time frame, and it cut through dozens of ty raps, wiring, and braided pvc tubing with no visible wear, let alone a bunch of "teeth" falling off.

Yes, no, kinda.
Sorry about the length of this thing.
HH

 

[eKretz]

First of all - I had assumed you were not comparing a coarse edge's "micro-serrations" as being literally indistinguishable from actual serrations, since that is just foolish. Of course they are not the same or even remotely indistinguishable. Asking such a question is akin to asking if 1+1=2. However, in the general sense - they are effectively the same in the way that they cut, both do basically cut with a sawing type of motion and effect. A clean, polished serration will certainly cut smoother than a coarse sharpened "micro-serrated" edge, but both are relying on the increased pressure concentrated at the high points of the edge to apply more force per unit area to help with the cutting. This discussion is getting a bit silly, so I will bow out at this point. I wish you luck with whatever your goal here is, however.

 

[unit]

I imagine there are plenty of other considerations for why the medical industry uses a finely polished edge

I bet you are correct, you have some interesting insight there (that I trimmed out).

---Trimmed for brevity---
Yes, no, kinda.
Sorry about the length of this thing.
HH

Thanks for the insight. As a guy that is always long winded, I do not mind the length of your response one bit!

I tend to agree with much of what you say (perhaps all).

Your scalloped blade example is a clever visual aid. I have no doubt that it could be QUITE effective in some uses. As an analog it would clearly demonstrate a point I was attempting to type (as a clear difference from a serrated edge). If your knife was a Wharncliffe (or any other "straight" edge with no belly or recurve), the sharpened edge would actually trend in 3 dimensions (viewed from the tip with most of the edge trending away or toward your eye, the edge would be visibly skewing both vertically and horizontally randomly (or at least as randomly as your scalloping pattern is)) as opposed to a macro view of a serrated blade which would trend in 2 dimensions (represented by the same plane as the back face of the blade).

Thanks for your insight and experiences! I truly appreciate it.

 

[HeavyHanded]

One last thing re traditional serrated edges - they are only operating in two dimensions if you hold the edge canted and look down across the back side of the bevel. If you center the edge and look straight down at a serration, you'll see that the cutting edge slopes out and back a little as you trace the curve of each scallop. So while it may be considerably more uniform, that aspect is not so different after all. If you want to view a true hybrid of the two, just perform the test with a rasp and a piece of hardwood, but only shave on one side of the edge. This will indeed look a lot like a traditional serrated edge if you only view a small stretch. Hit the other side and you get the whole mock-up. Traditional serrated edges also make up the entire edge bevel from one side whereas a ground edge makes it up with both sides. Arguably (or not) this actually centers the waveform of the cutting edge a little more than just cutting all the scallops from one side.

 

[Brisket]

They are different IMO. Can certain coarse edges mimic micro-serrations? Yes.

For those that think they are essentially the same, consider the coarse edge of a knife that has been pulled through one of those POS carbide v-edge sharpening gadgets. A closer look at the resulting edge would clearly show it to be coarse rather than a refined or polished edge yet the edge ridges in no way serve the same purpose as serrations.

 

[jimnolimit]

ok, i just ran my VG10 spyderco centofante 3 through a bunch of coarse grits. i used 60 grit silicon carbide sandpaper, 200 grit diamond, 400 grit diamond and 600 grit diamond.

the first pic is the edge with 60 grit @ 40x:

this is 60 grit @ 375x:

this is 200 grit diamond @ 375x:

this is 400 grit diamond @ 375x:

this is 600 grit diamond @375x:

 

[David Martin]

People need more real world experience. But atleast we're are trying to learn . Some trouble with that is there are some here that will think these assumptions have been tested and carry some weight . Whereas they don't and are merely throw out as discussion. Every farmer or rancher who has done much casturation knows the coarsely sharpened edge cut heals quicker, bleeding less. Than the finer sharpened edge cut. I'm sure doctors know this too as one told me so.
I'll ask my vet the grit those scalpels are sharpened to but he's told me and I remember it as 600 and run on a leather wheel to remove the burr and refine. Which isn't that fine but is enough to make them cut well. However, I've seen some coarsely sharpened edges cut very close to the same. Much depends on what grit type the two were sharpened on and the skill of the one running the knife, did he use a guide, was the machine kept in top tolerance, ect.. I've noticed my coarse edges cut both in the scallop and on the tips leaving no paper fiber residue on the blade. Even upon examination under magnification. Kinda blows another assumption here. But we're learning. Nor have I observed under magnification metal fragments broke off and left embedded in wood after being cut from a coarse edge. As I suspected this too. This causes me to realize the coarse edge can express good refinement. I'm sure either one coarse or fine could sluff off and leave metal fragments behind. Question would be, which is more likely. Again, it depends on the steel, how it was sharpened and stropped, ect.. A good topic to discuss here. DM

 

[jimnolimit]

I'll ask my vet the grit those scalpels are sharpened to but he's told me and I remember it as 600 and run on a leather wheel to remove the burr and refine. Which isn't that fine but is enough to make them cut well.

edge geometry plays a huge factor in the performance of a scalpel.

 

[David Martin]

Jim, Nice photos as well . I'd like to see some taken with the edge up too . DM

 

[jimnolimit]

Jim, Nice photos as well . I'd like to see some taken with the edge up too . DM

thanks.

focusing the scope looking directly down on the edge at high power is really difficult. i could take a better pic at 30x-40x.

 

[jimnolimit]

here is the edge after 600 grit diamond @ 30x-40x.

 

[Noctis3880]

A coarse edge is just a bad idea unless you specifically need it for say, tomatoes. And even then a true serrated blade would do better.

I've tried leaving a coarse edge for my coworker(P220 on WorkSharp) mostly because he complains about the knife being too sharp:thumbdn:. Less than a week later he complains that his knife won't cut anymore and he insists that he only cuts soft fruits and vegetables with it. A quick feel on the edge shows the edge rolled to one side. Stropping on cardboard realigned it, but I found that the edge could be pushed to one side with my thumb.

I had stropped the edge on my felt pad and cut into a felt block after I was done, so there shouldn't have been a wire edge left. My guess is that the "teeth" were strong enough to remain through the burr removal, but became weakened through regular use.

Thinking back on it, I can't say I ever remember any new knife I ever bought coming with such a coarse edge like that. Most seem like it was done on a paper wheel with a micro-bevel on the slotted wheel, so the grind lines are perfectly visible, while the edge is sharp enough to split hairs.

I can only assume that knife manufacturers have a good reason for polishing all their edges(not the whole edge, just the very apex of the edge).

 

[HeavyHanded]

A quick feel on the edge shows the edge rolled to one side. Stropping on cardboard realigned it, but I found that the edge could be pushed to one side with my thumb.

I had stropped the edge on my felt pad and cut into a felt block after I was done, so there shouldn't have been a wire edge left. My guess is that the "teeth" were strong enough to remain through the burr removal, but became weakened through regular use.

With all due respect, if the edge rolled at 220 grit then your inclusive angle is way too acute, your coworker was doing something abusive w/ the knife, there were large but well aligned burrs the length of the edge, or the steel is beyond substandard. If you could realign it with your thumb, I'd say the inclusive angle was a bit too ambitious. I've done fairly aggressive impact testing with a number of knives at differing grinds and the coarse edged ones (60-80 grit in this case) held up as well as a finely polished edge and at a steeper angle to boot(25 and 33 degrees respectively). I have never seen the "teeth" on a rough edge become weakened due to use, not even on a machete after pretty hard use. I have seen an edge roll over that weak when done at sub 20 degrees (16 degrees inclusive), the entire edge folded and fractured off like foil at the first bit of lateral force. This was on an $11.00 Mora, so steel quality may have played a large factor.

It can be quite challenging to remove the burr completely from a coarse edge, as the topic of another currently running thread is exploring.

Thinking back on it, I can't say I ever remember any new knife I ever bought coming with such a coarse edge like that. Most seem like it was done on a paper wheel with a micro-bevel on the slotted wheel, so the grind lines are perfectly visible, while the edge is sharp enough to split hairs.

That's how many come, but not all. The knife I now EDU (from TOPS) came with what looked to be about an 80 grit edge that appeared to have not been hit with a paper wheel or any other powered finishing equipment. I "refined" it down to 120 grit where it remains, and the edge was tough enough to survive being dropped about 4 feet edge first onto my garage floor with just a small ding to show for the experience. The floor actually showed more damage than the knife. This edge is right around 28-30 degrees inclusive.

HH

 

[David Martin]

It takes some experience to pull off coarse edge sharpening . I can't recall seeing a polished edge coming from my factory knives. Gerber, Buck, Case, Schrade, ect.. They have all looked more coarse. DM

 

[unit]

this is 200 grit diamond @ 375x:

Thanks for the images. Did you notice that horizontal feature in the bottom left of your work in this image? I think it may be present but harder to see on the right side also.

 

[David Martin]

Jim, Thanks for the edge leading photo #32. It looks straight to me . Somebody has some good sharpening skills . In Dr. Verhoeven's studies and photos I've seen the 600grit edge look very jagged but then became very refined after a few passes on a leather wheel. So, those make a huge difference. DM

 

[jimnolimit]

Thanks for the images. Did you notice that horizontal feature in the bottom left of your work in this image? I think it may be present but harder to see on the right side also.

your welcome.

there is a chance those features (i think) are dust/micro debris, but i can't really say for sure. taking those pics are a slight pain because i have to wipe the blade off alot to get a clean shot. any micro debris will show up fairly large. i will give you an idea:

here is my buck vantage pro:

here is the name "buck" that's etched on the balde at about 40x:

here is the small dot in the upper right-hand corner at about 375X:

 

[jimnolimit]

Jim, Thanks for the edge leading photo #32. It looks straight to me . Somebody has some good sharpening skills . In Dr. Verhoeven's studies and photos I've seen the 600grit edge look very jagged but then became very refined after a few passes on a leather wheel. So, those make a huge difference. DM

thanks man.

it's a kinds funny story, my centofante 3 went through quite a few "sharpenings" while taking those photos. at first i went through 60, 200, 400, 600 and took all the pics. when i was saving/uploading the pics i accidentally erased the 60 grit @ 375 pic. so i went back and re-did the edge at 60 and took another pic. after that i ran the knife back through the 200, 400 and 600 because i didn't want to leave the edge at 60 grit. the edge leading pic was taken last after i went through all the grits twice.

i didn't for the photos, but i almost always strop my edges on newspaper after sharpening. also, if im sharpening and i start to build up a decent burr, i will run the edge through a rolled up newspaper or a piece of wood lightly 1-2 times to remove the burr and then i will continue to the finer grits. all the pics took were "as is" right off the stone. i just wiped the edge off to remove foreign material.

 

[David Martin]

Jim, Good job and thanks for the time and effort . DM