sharp vs ultra-sharp

[butcher_block]

yep dave sure knows his stuff and when i hav a single bevel that the new buyer is not one to hone his self it goes to dave to get it ready and i pay for the sharpening

one has to know what they are good at and what they are great at ( i can make knives and do a good job at honing but all the sheath work and super honing get done out of house )

 

[Todd Robbins]

I just did an informal "test" to compare a polished edge with one not quite so polished. I didn't measure the force needed to cut, nor did I count the amount of material cut, since this was just to satisfy my curiosity. I cut up quite a bit of cardboard left over from Christmas gifts, enough to completely fill 2 100 gallon trash drums with 1" strips.

I used a kiridashi with a 2" cutting edge that I made from 1095 and heatreated using a digitally controlled heat treat oven, soaking at temp for 10 minutes, and quenching in brine. I tempered once in my home oven at 375 degrees and twice in the heat treat oven at 415 degrees. The bevel is flat ground very thin.

For the polished edge I sharpened first to a fine burr on an EZ Lap fine grit diamond stone, then stropped on a piece of leather glued to a board that was loaded with green buffing compound, then on another piece of leather on a board loaded with white compound. The edge and lower 1/3 of the blade was basicly mirror polished at this point and would easily treetop hair and slice toilet paper without tearing.

For the other edge, I sharpened to a fine burr with the diamond stone, then removed it and stropped with medium pressure, 20 strokes on each side, on the leather loaded with green compound. It would easily shave hair, but not treetop it, nor would it slice toilet paper.

I repeated the test twice just to confirm the initial results. I found that the polished edge degraded slowly and consistently to the point that it would begin to tear the cardboard. I was surprised at how long it took to get to that point.

I found the less polished edge to degrade noticeably from it's initial sharpness rather quickly, but then it seemed to maintain a level of sharpness that would catch my thumbnail but would not shave hair for a very long time, much longer than the polished edge.

The polished edge required noticeably less effort to cut initially than the less polished edge.

I think that the type of cutting you intend to do should dictate the type of edge you choose. I plan to do some rope cutting soon in a more detailed, measured manner to further test the two edges used here, and I am satisfied using the less polished of the two on me EDC for now. It will cut longer overall for me, and it takes a whole lot less time to sharpen- ten strokes on either side on the stone and the same stropping regimen brought it back to initial sharpness both times.

 

[hammerfall]

Large unruly carbides will result in an edge that will either start out ragged, no matter how you try to sharpen it, or will quickly wear into a nasty micro saw that can still tear its way through things but fine cutting is lost. One can make these blade look like they stay sharp longer by carefully choosing targets that saw and tear more easily, paper, rope, some meats etc… The same is true of certain welded blade materials, cable, pure nickel and twists with instable weld zones, to name a few, or heavily segregated tool steels and blades cut from sheet perpendicular to the anisotropic rolling directing.

i had tried to explain the same thing to some smith in my town. but few of them believes it. they rather believe the forge welded pig iron has some magic empowerment...

One famous traditional bladesmith over here had play a trick by cutting rope 10k times, then still be able to cut papper. he and his follower use it as an evidence to prove forge welded tamahagane is supperior steel than modern tool alloy. and he got more people beliving him than believing jesus.

 

[wnease]

I've wondered about this before. Generally speaking, aren't the mechanical properies better in the rolling direction? If so, wouldn't that mean better properties if the blade is oriented so that the rolling direction is from spine to edge?

I've wondered about this too, especially since I started making blades of unidirectional fiberglass (with steel edges), putting the fibers perpendicular to the edge near the core and parallel to the edge on the outside...

 

[hammerfall]

if i remember right the "anisotropic" is caused by the fiberous impurity and carbid bands formed during rolling progress. carbid and other impurity has better dispersion parallel to the rolling direction, and worse on other direction. it make the blade strong on one direction, weaker on others.

to solve this problem, buy ESR or higher level steel with higher purity. you can get carbide a better dispersion by thermal treatment. also, forging can make the fiberous direction go along the shape of the blade, and futhur refines the carbid and grains.

 

[Kevin R. Cashen]

I've wondered about this before. Generally speaking, aren't the mechanical properies better in the rolling direction? If so, wouldn't that mean better properties if the blade is oriented so that the rolling direction is from spine to edge?

A blade oriented as such would gain in draw or saw type cutting as the edge degraded in accordance with those directional properties, but this would be at great expense in lateral impact toughness. A blade with the rolling direction parallel to the length (from tip to tang) will take and hold a very fine polished edge much longer and still benefit from better impact strength.

The ability of forging to reorient the anisotropic effects of the rolling mill is greatly overestimated*. Just take two different colors of modeling clay and stack up multiple layers, stand it on end and work it down in the perpendicular direction, the layers will not reorient themselves in a new direction but will instead get distorted more like a "W" pattern damacus. If one wants to totally reverse the anisotropy, multiple folds and welds would be necessary, once again just like you see in damascus, so it should be quite obvious.

*edited to add: before readers of some of Verhoevens papers spins in a tangent on reorientation of cementite sheets in wootz, carbide is susceptible to diffusion, anisotropy from welded voids, inclusions and other artifacts are not.

 

[Kevin R. Cashen]

... play a trick by cutting rope 10k times, then still be able to cut papper. he and his follower use it as an evidence to prove forge welded tamahagane is supperior steel than modern tool alloy. and he got more people beliving him than believing jesus.

I have pointed out much the same thing here in the U.S. many times, there is testing and then there are "exhibitions" that conveniently use methods and materials chosen specifically to make the knife look good, that would be called marketing.

 

[hammerfall]

just some thoughts. if you twist a round bar during the forge, cause a large dislocation on planes vertical to the fibous direction. since forging also pulling the blade from tip to tang, that should increases the dispersion on almost every direction. would a blade made from a twisted round bar has less anisotropy?

 

[hammerfall]

*edited to add: before readers of some of Verhoevens papers spins in a tangent on reorientation of cementite sheets in wootz, carbide is susceptible to diffusion, anisotropy from welded voids, inclusions and other artifacts are not.

i had also done some study on wootz. i think anything is susceptible to diffusion, somehow the rate of difusion depends on temperature and time. for example, there are a some low carbon steel also shows banding structure on the surface. the result of this is the inclusion of P. homogenizing anneal at 1200 C for 2 days can remove the banding structure caused by P.

 

[DaveMartell]

This subject of polish vs toothy edge is like (to the knife community) talking religion or politics. I won't force my ideas onto others here but I'd like to share some thoughts and advice.

A little philosophy...
Picture what happens when you visit a friend's house who spent all day cleaning the place making it spotless. Do you walk in and think, "Hey, this place is spotless!" I doubt it. He/she spent all day cleaning yet it's likely that no one will notice.

Now visit another friend who's house is filthy and there's a real good chance that you'll walk in and think to yourself, "Damn, this guy's a pig!" The filth is a negative impression versus a positive impression you receive from the clean house. The thing is that the positive impression from the clean house isn't something that you consciously think about, that's because that person met your needs whereas the filthy house person didn't and this struck you even though you weren't looking for it.

The same is going to be true of the customer noticing a crappy edge. They'll never notice nor likely appreciate the time you put into a good edge but they'll always notice and recall that bad edge. The reason is that you either meet their expectations or you don't - plain and simple.

IMO, many knifemakers that I've spoke to over the years have undervalued the role that the edge that they apply to their knives plays in the big picture. Imagine that you sent a knife out to customer who dropped $500 on it and they get to cutting and within seconds to minutes the performance drops off, the knife has low edge retention they think. This is a very real scenario most often caused by poor sharpening but the customer only knows that the knife stopped cutting correctly so they might think your heat treat is off - yikes!

The edge is one of the last things that you do before wiping the knife clean and cashing the check yet it's one of the first things that your customer will check out so why not put some effort into getting it right?

Now what's right you ask? Well, the obvious answer is to match the edge to the task at hand. Just like you thought about steel selection, heat treat, geometry, and profile you must also factor in what you want from your edge and execute this cleanly.

A few things to consider (in this order)....

What is the knife likely to cut?

What's the geometry of the blade?

How do I want the knife to cut? Slice, push, (if a kitchen knife) slice/push cut?

How long do I want the edge to last at the level to which I created?

What steel is used?

What's the hardness value?


These answers are what should be used collectively to determine what level of finish an edge is brought to, what angle is selected, what grind type (convex/flat) is chosen, and also how you apply these things regarding your methods/tools used.

It's my opinion that most edges are either over buffed (meaning rounded over or ready to go smooth upon wear), left too coarse (ready to crumble or fold), and/or nor properly de-burred.

I've been very lucky (although sometimes it doesn't feel like it) to work on Japanese kitchen knives because I get direct feedback from nearly all my customers. These knives are difficult to sharpen, very difficult to de-burr, and used heavily. They get pounded on day in and day out and only the very best edge matched for the task at hand that's been executed perfectly will survive. When I first started we all thought I was doing great because I was getting the edges to last a whole 12 hr shift in a pro kitchen while today we expect the edge to last weeks of 12 hr shifts with nothing more than a stropping. The knives offered great geometry, steel, heat treat (well kinda') but I had to figure out what the edge needed to match these qualities before the knives could perform at a high level. Yes, I could pass them on a paper wheel and shave arm hairs on day one but arm hairs isn't what the chef is looking to cut. I needed to find out how the knives would be used, what cutting boards were being used, what food types were being processed, and what the chef was looking to see be it texture, food release, ease of slice/push cut/combo and then work to create an edge that matched these conditions.

So with that I suggest that you work towards matching your edges to what you and your customers expect from the knife's use. If you're unsure then start testing but better yet put a knife you made into the hands of a potential customer and ask them for feedback and go from there.

One thing that I know for sure is that after having sharpened so many knives and studying the edge they way I have is that I know that I can always do better and likely so can you.

If anyone ever wants to talk sharpening or needs some advice my door is always open for a PT or email, just don't call as I'm not in.

Dave

 

[Tippet]

Interesting point Dave, and for the many people who enjoy praise from others it's certainly pertinent. From my perspective, since I try to keep my kitchen knives super sharp, I really notice when they're less so. I mean it screams at me. Just like when I get home to find a messy house. Doesn't matter if I spend all weekend cleaning it up or spend the same amount of time throughout the month just keeping it clean, it's clean and I like it that way. haven't got any idea what my visitors think about it, never asked and they;ve never mentioned it.

In terms of getting an edge on a knife to sell, seems to me most knives I've bought are poorly sharpened. With the exception of a few Japanese knives I've bought from JCK and JKD, I've never bought a knife that was properly sharpened from the get-go.

I paid Gil Cote for two custom knives, one cost $425 and the other went $475- and both had mediocre edges at best. Unfortunately there were enough other problems that the lack of a really fine edge didn't even register at the time. So maybe the key to avoiding complaints from customers about the edge is to do a crappy job on the other aspects of the knife.