How Sharp is Sharp Enough?

That's the exact answer I was looking for ;)
 
knifenut1013 said:
Sounds good but still explains nothing.
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I think that Md 25v explains it very well. Sharpness, as you point out, can be relative to the user. What is sharp for you, may not be enough for me. I can get knives extremely sharp, so it takes more than diafolds to achieve what I would call "very sharp". Yet, I could just as easily sharpen a knife on cinder block to where it would perform well at most tasks.
 
Exactly, sharp enough is individual to us all and closely related to our sharpening skill. Sharp enough for me was once a medium grit arkansas stone and now it 15k diamond polish. I like a high polish because of the way it cuts but also know proper form of a bevel can often mean more than the grit you finish, similar to your cinder block example.

I guess its one of those questions there is no right or wrong answer to considering its something you can only answer yourself :)

We know because of experience,
 
Disregard that last line, not sure how it ended up staying. it was something I started to say but thought I deleted :(
 
Md 25v said:
If your not satisfied with any particular edge then you continue to refine that edge until you are.
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Unfortunately my skills don't allow me to get it as sharp as I want which is to be able to cut a single hair by putting it on the edge and just pushing down just like I've seen on some videos.
 
What about for people that are sharpening knives for customers? How are you supposed to judge what is sharp enough if you don't know what they're cutting and how they want to cut it?

I mean, certainly there should be a general set of guidelines right?

I mean, let's put it this way:
(All hypothetical)

I'm a meat packer and I work all day cutting up slabs of cows and pigs. I want something that works with as little force as possible, but that is also going to stay sharp all day long after I've cut through possibly hundreds of animals.

How sharp is "sharp enough" for me?


I mean, in that regard, what if a meat packer asked you that question when bringing his knife to you. Fact of the matter is some people just don't really know how sharp their knife could be and then when they finally start thinking about how sharp it should be they reach these levels of confusion.


I mean, if I picked up wood working a lot more tomorrow, am I going to realize that the edge on my chisel needs to be more polished? I'm not a skilled wood worker or anything, so I just might not know. On the other hand if someone told me that I need it this sharp to do this first, that gets me started down the right path.


So maybe general guide lines? How sharp is "sharp enough" for:
Dock workers
Wood workers
Meat packers
Ranchers

Etc.


Anyway, just curious, because I've never really gotten a lot of input from various workers in those profession as to waht type of edge they like except that it seems wood workers like a nice polished edge to maintain the finish on their wood, and there seems to be a big advantage to reducing friction in the meat packing industry.
 
When someone brings me a blade it is sharpened for the steel, geometry, and use.

The understanding of what you can do with your sharpening angles and level of edge finish with the above mentioned considerations are the deciding factor in the finished product. If I'm handed a cheap mass production plastic handle butcher knife a extreme polish job at 10 degrees per side is probably not the best idea. A cheap blade as such would be steeled several times a day so just resetting the bevel and getting it to "shaving sharp" would be good.

Now if it was a Phill Wilson custom in CPM-S90V it would be a different story. 10-12 per side with a little slop in the angle control to produce a slight convex with a leather strop finish to 1 micron would most likely be my choice. There would also be instruction on how to care for the edge because a steel would drastically reduce its performance and cause possible damage.

If you wanted to cut all day you need the better blade. A cheap blade no matter the sharpening would not last per your example.
 
dphillips said:
Rick,
I am not familiar with lapping paper. How thick and stiff is it? And do you back it with anything?
Thanks,
Donavon
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It is a film actually... so like a thin sheet of plastic. I back it on a pane of glass, or lay it over my 8000 stone. You can also strop on wet paper... newsprint amounts to about 10-12,000 grit, I believe, depending on clay content.

I will add that I do all my hand sharpening (400grit+) away from the edge in a stropping motion. Very similar to Murray Carter's technique.

I don't use any guides or jigs for sharpening and I really don't pay much attention to bevel angles, either..... I just go by feel nowadays.


Rick
 
Magnussen said:
That is not true at all. Infact it is quite the opposite. If your knife edge becomes weaker with fine polishing, you are not sharpening correctly. Folk's first mistake is thinking they need to alter geometry to get razor sharp. When they work at a hair popping edge, they unknowingly lower the angle or they do not remove the wire edge completely.

You have to understand what is happenning as you sharpen. Things are happening at a scale that the human eye cannot pick up. You have to go by feel and more importantly... know what to feel for.

If you are serious (and perhaps a little obsessed) about sharpening. I recommend getting a jeweler's loupe... Then you'll be able to see what's really going on.

Rick
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IMHO this statement being true or not depends on the grade of steel, temper, and the material being worked upon. For example, I put a CRKT Crawford Casper folder that I believe is Aus6 to a 200 grit diamond stone using a single bevel at approx 25 degrees. It cut through a pressed-paper skid corner (the type that are commonly used under a layer of shrinkwrap at all four corners) using an aggressive swing. It made the cut and appeared no worse for the wear, cut through a few pieces of cardboard afterward with no hesitation. Honed the same knife down to 12,000 grit at a 35 degree bevel and performed the same test. The edge didn't fold, but a piece of the edge about 2mm long broke off to a depth of about 1/2mm where it made contact (it did complete the cut). Performed the same test with the same edge bevels and grinds on a Kershaw Salvo using 14C28N Sandvik, a Benchmade 722 with 154cm steel, and a CS Voyager with VG1. All passed wth no damage to the edge. All blades were examined under a 30x loup before and after. Plenty of variables, I undoubtedly had variance in grip pressure and striking angle etc, but you have to start somewhere. I am confident my angles were accurate and the edge preparation was clean. This also mirrors my experience with tools I've used to clear the vines on the more overrun parts of my property. With the exception of an old Austrian corn knife that has become my favorite "machete" in spite of it's light weight, all my cutters last longer with a coarse grind. Now if I were cutting meat it would undoubtedly flip the other way and the finer edge would cut longer and with less effort. There's a big difference between meat and wild grape vines, and an equally big difference between a hard swing and a steady press. Also, with a broad enough angle, virtually any cutting tool using respectable steel and sporting a highly refined edge can withstand a tremendous amount of abuse. I hone my 17" camping hatchet on a translucent Arkansas stone and it stays sharp for several hikes with plenty of use. However, at these larger angles the ability of an edge to cut easily through most materials begins to drop off, even as it can still shave the hair off your arm...
 
HeavyHanded said:
IMHO this statement being true or not depends on the grade of steel, temper, and the material being worked upon.
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From my personal experience as well as several of my customer's and colleague's, I still disagree with this. I agree that the steel, heat treat and edge geometry have to suit the task... but sharpness should be polished and honed to highest degree you can accomplish with the tools you have.


HeavyHanded said:
For example, I put a CRKT Crawford Casper folder that I believe is Aus6 to a 200 grit diamond stone using a single bevel at approx 25 degrees. It cut through a pressed-paper skid corner (the type that are commonly used under a layer of shrinkwrap at all four corners) using an aggressive swing. It made the cut and appeared no worse for the wear, cut through a few pieces of cardboard afterward with no hesitation. Honed the same knife down to 12,000 grit at a 35 degree bevel and performed the same test. The edge didn't fold, but a piece of the edge about 2mm long broke off to a depth of about 1/2mm where it made contact (it did complete the cut)..
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I'm curious as to why you felt the need to change the bevel angle to 35 degrees.... and why you would compare the two cuts? The 35 deg bevel would most certainly need more pressure to perform the same cut. I will have to take your word for it when you say that your had a proper edge finish and the knives were properly heat treated..... but it does not add up, to me. What type of material was backing the skid corners when you performed the cuts?

Also, when you say angles of 25 & 35 degrees..... do you mean inclusive or per side? I just need to be sure we are on the same page, here.

HeavyHanded said:
Performed the same test with the same edge bevels and grinds on a Kershaw Salvo using 14C28N Sandvik, a Benchmade 722 with 154cm steel, and a CS Voyager with VG1. All passed wth no damage to the edge.
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Same test? at 25 degrees or 35 degrees?... polished or toothy?


HeavyHanded said:
This also mirrors my experience with tools I've used to clear the vines on the more overrun parts of my property... all my cutters last longer with a coarse grind.
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Can you explain your method for sharpening to a fine polished edge?



Rick:thumbup:
 
I do the tomato thing too.

I've been contemplating sending all of my knives to some real mean looking guys that strop on car hoods I'll tell them to make them sharp enough to skin a hand grenade.
 
Magnussen said:
I'm curious as to why you felt the need to change the bevel angle to 35 degrees.... and why you would compare the two cuts? The 35 deg bevel would most certainly need more pressure to perform the same cut.
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I was testing a few assumptions, namely that the coarse edge at 25 degrees would have durability issues when used in a percussive manner (it held up fine in all cases). Secondly, that 35 degrees for a fine edge should hold up very well and require less energy than a coarse edge at a thinner angle (it did cut with less energy, but did not hold up as well in all cases).

Basically, I was setting out to prove my casual observations concerning highly polished edge treatments were false.



Magnussen said:
I will have to take your word for it that...the knives were properly heat treated.....
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I'm stuck taking the manufacturers at their word

Magnussen said:
... but it does not add up, to me. What type of material was backing the skid corners when you performed the cuts?
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Nothing, they were supported 12" below the cutting area and all cuts struck the outside curved edge (for maximum difficulty) where a blade would have the toughest time biting into the pressed paper and the material would be at it's most dense.

Magnussen said:
Also, when you say angles of 25 & 35 degrees..... do you mean inclusive or per side? I just need to be sure we are on the same page, here.
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Inclusive.


Magnussen said:
Same test? at 25 degrees or 35 degrees?... polished or toothy?
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Yes and yes. All knives were tested in the same manner.




Magnussen said:
Can you explain your method for sharpening to a fine polished edge?
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Starting with as coarse a stone as needed to establish an initial bevel at 25 degrees inclusive, I move up to a 200 grit diamond stone with the same single bevel. If the knife is for hard utility use, I stop right there. If it needs a more refined edge I proceed on to a 750 grit diamond stone for the new primary bevel at 35 degrees. For day to day use I stop here. If needed, I move on to my "soft" Arkansas stone (approx 1000 grit) and then to a translucent Arkansas stone that is somewhere around 8000 grit (finer than a 6000 grit waterstone). The finishing touch is done on a Franz Swaty hone (approx 12000 grit). I stopped using strops and the leather belt on my sander, but have used diamond lapping compounds down to 1/10 micron. Even under a 30x loup I cannot see much difference between the Swaty and a strop, cannot tell the difference in use except for shaving, and I find it requires more upfront work to re-edge a compound-polished knife than one honed on a stone. All my honing is done edge first and by hand, which naturally results in a slightly convex edge, though I try to limit that effect as much as possible.

It is my belief based solely on my own personal experiences that there is no one edge preparation that works best for all tasks. The highly polished edge can be detrimental to long life in some applications much as a very coarse edge can fail to perform at all for some tasks. Even a hand saw needs to have it's teeth set and edges filed based on the intended wood to be cut. It will perform anyway, but we're talking about cutting efficiency and effective lifespan between maintenance here. On tightly woven or braided materials a highly refined edge can slip right across it without catching, and try press-cutting something soft with a coarse edge. Now if you take the woven material and press down on it, the fine edge will part it, and a coarse edge drawn across a soft material will saw right into it. Taken to an extreme, consider how many people swear by their fully serrated knives. As I said in an earlier post, there's a lot that goes into how efficiently a knife will perform a given task, that's why after several thousands of years, there's still no consensus on what works best and everyone that takes a close look at the subject comes to their own conclusions.
 
A well written and thought provoking post, HeavyHanded..... thank you for taking the time to answer my questions.:thumbup:
 
Hairpopping sharp is fine with me. I can't recall ever needing a knife to whittle hairs but It sure is neat to see other people do that.
 
Scott Free said:
I recently purchased a Diafold Coarse/Fine sharpener and am very happy with it. I am now able to put edges on my Moras in the field that will shave the hair on my forearms. Diafold also sells an Extra Fine/Extra Extra Fine sharpener. I'm tempted to go to the next level, but how practical is it really? I might be able to show off to my friends, but does it really add much to the function of a user woods knife? How sharp is sharp enough? Does an "extra extra fine" edge last? Or will I be back to where I am now after just a few cuts?
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If you're happy with your results, save the money or use it for something else.

There's a sensual feeling one gets cutting food with a waifer-thin piece of steel sharpened with abrasives much smaller than blood cells and there's a practical reason to use the same such edge (or much finer) on a straight razor, but any extremely sharp 600 grit edge is still an extremely sharp edge.
 
Magnussen said:
A well written and thought provoking post, HeavyHanded..... thank you for taking the time to answer my questions.:thumbup:
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Thank you for encouraging me and reading with an open mind. Facing repeated opinions from folks that swear by the highly polished edge make me keep testing my own assumptions. Nothing is written in stone, you obviously hold the views you have based on your own personal experiences, the same as me.

Every couple of years I get off my backside and do some more testing. Only recently did I change my views of what makes for the best SD edge, based on a retesting of an older series of trials I did on free-hanging and foam backed denim and leather. Next on my agenda is an exhaustive test on how changing the direction of grind relative to the cutting edge, changes how a knife performs. It'll take me a year or two to get around to that one...;)
 
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