Question on Sharpening.

[akee]

Due to the different grain sizes of the modern day alloy steel, would it mean that ultrafine whetstone and stropping would be a waste of time when sharpening certain coarse grain steel? If so, which are the coarse grain steels and which are the fine? Thanks for any input.

kee

 

[Knife Outlet]

It has nothing to do with the "grain size" of the steel. It has to do with the "grit size" of the abrasive.

Sharpening is a matter of grinding one or two bevels of an angle appropriate for the steel in use and then smoothing or polishing those bevels to whatever one prefers or whatever is appropriate for the knife's intended use. I polish the bevels on my Japanese kitchen knives to #8000 grit. They are like razors (well really smoother than razors) for making thin cuts with food products. On the other hand, it wouldn't make a lot of sense to put that kind of edge on a camp knife. In that case I'd use 25 degree bevels and 220 or 320 grit abrasives.

So concern yourself with the hardness of the steel and the intended use of the knife. Don't worry about how the steel was manufactured. Take care.

 

[HoB]

There is the misconception of what coarse grained steel means. Even if it is coarse grained the grain size is generally smaller than the finest abrasive grit that is available. There may be exceptions and Cliff Stamp would probably know, but in all generality you should have a hard time refining an edge by sharpening to the grain limit of the steel.

 

[T. Erdelyi]

I think it comes down to some blade grinds work better with a toothier edge caused by a coarser stone, while others lend themselves to a more refined, polished edge.

Intended use would be a better deciding factor over how refined your edge should be.

 

[Jeff Clark]

Don't listen to those guys, they don't know what they're talking about. If you compare sizes of grits and the sizes of the carbides you would think that you can get any blade equivalently sharp using a fine hone and a fine strop. Experience will tell you that is not so. For example I sharpened a cheap Chicago Cutlery chefs knife for a friend this weekend. I wanted to make a good impression so I made it as sharp as possible. I took a belt sander and reprofiled the edge down to about 10 degrees per side. I used 100, 220, 320, 400, and 600 grit belts to make the reprofiled bevel meet right at the edge. Next I deburred and polished the edge to about 12 degrees per side using a 1000 grit Shapton Professional water stone. I finished off with a moderate number of light pressure strokes on the medium and fine Sharpmaker ceramic rods. On a good steel this blade would have had a very nice shaving edge. On this bad steel the blade would just barely shave.

Even on a bad steel I finish the blade including using a fine ceramic rod. If I don't like the edge at that point I go back and roughen the edge with something between 600 grit and the medium Sharpmaker rods. I experiment with a little stropping. Sometimes stropping seems to dull the edge on high alloy stainless steel.

 

[Knife Outlet]

Jeff, you sure didn't do your friend a favor. After grinding off more steel than you should by fooling with all those belts, you cut the bevels to an angle that steel of that softness won't support. Those edges would simply fold against a cutting board. 20 degrees would have been a minimum angle for steel like that - perhaps even 25. The results you had, by the way, were a result of this error and poor quality steel. They had nothing to do with "grain size"
which, by the way, isn't the same thing as the size of the carbide particles.

Incidentally, if you dull your edges on a strop then that results from one of three problems - leather that is not attached to something hard and flat, leather that is too thick or rounding the edge by turning the blade inappropriately during the process. Since you use waterstones, I'd recommend simply getting a fine finishing stone and using that instead of the strop. It would be a good complement to your 1000 grit medium stone. Take care.

Fred
Who doesn't know what he's talking about but still manages to sharpen kitchen knives commercially.

 

[Cliff Stamp]

There is the misconception of what coarse grained steel means. Even if it is coarse grained the grain size is generally smaller than the finest abrasive grit that is available.

For most decent cutlery this is true, the grain size is generally small, even the worse which is D2 which has large segregated carbides comes in at the tens of microns. The only way to see this effect is to sharpen at really low angles. I have brought ATS-34 for example way down to 5 degrees per side and you can see the edge break out as it can't get fine enough as its too coarse.

However when you go to cheaper stainless steels like Jeff noted, all bets are off. I have seen some cheap ones actually degrade visibly, as in you could see by eye the huge burr and breakouts. I just sharpened one this week that would not get any finer than the fine side of a hockey puck stone. After using the coarse side to set the edge I attempted to polish it.

I spent 15 minutes trying to remove the very coarse teeth and refine the finish. It did nothing, the edge just kept breaking away. I finally just really upped the angle to about 25 degrees per side and gave it a few passes and left it alone. I would have just filed it, however it was too hard to file - odd combination of properties.

Jeff have you seen any like this, what do you usually do with them?

-Cliff

 

[akee]

D2 which has large segregated carbides comes in at the tens of microns.

As I understand Chromium oxide particle in the stropping compound measure 5 microns.

So in effect, when sharpening D2 blade, the moment you reach the sharpness of the independent existing carbide, that is at tens of microns. Wouldn't it mean that from this stage on , the more you continue to sharpen the less productive it becomes? Since it will merely break the carbide away?

kee

 

[Cliff Stamp]

Chromium Oxide is ~0.5 micron, there are a few abrasives this size or smaller, some AO and some diamond dusts. If you check archives on the wood workign newsgroups, where people are *very* particular about fine edges, you will see them note than on certain steels, it doesn't get productive to go past a certain point. it is angle dependent though, at really high angles you can get fine polishes even on coarse steels. it also depends on the heat treatment of the steel, so you need to just check and see. Does the edge respond better to a higher polish or not.

-Cliff

 

[Quy4n8]

Very good thread. Once again I am learning quite a bit. For normal everyday use, cutting whatever may need to be cut, does grain size of the steel make much difference? It makes sense for specialized tools, such a wood carving chisels, but what about the pocket knives most of us carry. If so, then this seems to get quite complex, since grain size is not just a matter of the steel, but also the heat treat involved. Is there a source where we can learn more about grain size and what different heat treats do to grain size? Thanks.

 

[HoB]

Well, first of all it is important to distinguish between carbide and grain size...which I didn't do in my first post either...I appolgize. Most stainless and high carbon steels are sintered these days, even those that are not CPM steels. During the sintering process to obtain maximum performance from the steel, maximum grain growth and desification is usually a wanted property. Again, there are exeptions, especially if a porus structure is wanted (like gray/porus, white/closed pores sharpmaker rods). The grain structure is also affected during the heat treat and cryogenic cooling. The carbide size is the aggregation of the carbides within the steel and usually a well dispersed small carbide structure is wanted. Having said that, I don't know, which of the common steels have which structures.

Jeff, I totally share your experience. My housemate has a few knives that hold a sentimental value to him, and I hate them because the steel is so poor that you can't get an edge no matter what, but I doubed that that is due to grain size. Even among the steels that is mostly talked about on this forum I find that I am not a fan of 420HC because the in my experience the edge rolles way too easily, even during shapening, while I find that only Shirogami (white paper steel) takes an edge as easily and keeps it, as the A2 knife from Bark River I recently got, even though both steels are hardened to a much different degree. So there is definitely a difference. But also from experience I must say that I see a significant improvement in an edge finished on a 6000-10000 grit stone over one that is finished on a 3000 grit, whether the steel may be ATS-34/55, A2, CPM30V or VG-10. But I don't play around with angles too much, I sharpen most of my knives to 30 deg included, with some that see abuse at 40 deg.

But that's only my $0.02.

Duh, I should have read Cliff's last post :footinmou. I read the same thing about the woodworkers...but I would like to point out that there definition of polished edges is quite amazing. They are arguing over whether or not you should go from 5000 grit to 8000 grit or to 15000 or even 30000 grit .

Richard: try "Sintering Theory and Practice" by Randall German. It doesn't say much about heat treating but a lot about activated solid state sintering used for many high carbon steels, and liquid sintering used for many carbides and stainless steels. But it doesn't talk about specific steels. I wouldn't be surprised if that information would be hard to come by as it is proprietary.