would you try using the file to sharpen the A2 plane blade? No, because it's not hard enough to cut efficiently. Same goes for the file vs. the sandpaper against the welding table. The file is nowhere near as hard as the sandpaper's abrasive, so of course the sandpaper will cut better over a large surface area
eKretz. I'm treading into dangerous water here, because you're the machinist. So I look forward to your thoughts on this.
The file is supposed to be harder than the welding table, in my example. If your welding table is harder than a file, please just imagine a different welding table that isn't. In my country, hot-rolled steel has such low carbon that it can't even be heat treated to begin with. (It has to be, because it is used for structural things. And if it had too much carbon, welds would fail. I think it's spec'ed btn 0.3-0.6%, or maybe that is for common rebar? I can't recall, now). I would guess rc hardness in the 40's, scratching on the 50's at best? Furthermore, let's say the surface oxides have all been freshly ground away, so there is nothing funny on the surface.
The file will still slide over the table without cutting. It's because of the geometry. The file was optimized to make quick work of a smaller area of cut on this material. That's what the teeth were sized/shaped/spaced to do. When you try to use the entire face at the same time, it doesn't work. It's similar to having too high a TPI in a cut. You just spin your wheels, and your saw blade will just overheat and dull. No matter your feed rate/pressure, no matter your surface speed, it just won't work. Even if we give the saw infinite beam strength so we can jack the feed pressure as high as we want, well there's nowhere for the chips/swarf to go. The saw gullets will choke on the chips and rub and drag those chips against the stock. That 40 tpi saw trying to cut the 4" round, it needs to come up for air, sooner than that. It can't make that thickness of cut.**
The sandpaper doesn't cut because it's harder. It cuts because it starts out uneven to begin with, and particles break off and roll around between your sanding block and the welding table. This second bit is called lapping. And the lapping process can technically cut over an infinite surface area of cutting/contact if you are patient enough, although it will possibly have some practical limit, too. This is even better if you use some oil so you don't lose your abrasive grit.
But if you take a 1/4" thick plate of hot-rolled chucked in a vice? I'll take the good file which is optimized for fast removal at this task, over any sandpaper you want. All day, every day. The file will be faster. There's hard enough, and there's harder. OTOH, there's also geometry. Let's say the sandpaper is sharper, because we can use and throw away as much as we want. Clearances. The file has way better clearances by design. The sandpaper has just points that plow throw the material. Rake angle. File by design. Gullets i.e. swarf clearance. File by design (now that it's within its stride). The file will run circles around the sandpaper. The file is now in its element, like the barracuda in the deep sea.
Added: The soft arkansas isn't so optimal, of course. It cuts like a bad file, but that's still good enough for what we need in order to make great edges, as long as we use it within its scope or sweet spot. Although it's a bad file, it's still way better as a file than it is as a lapping stone. To lap, you need lapping paste/grit. Finally, even a bad file can potentially still cut faster than lapping, as long as we stick to the right cuts. This is because lapping is inefficient. For the amount of work input, not a lot happens, compared to direct abrasion/filing. A more accurate way to state that in a physical sense might be to say: for the amount of work, a lot more "other things" happen aside from material removal, compared to direct abrasion/filing. OTOH, the lapping stone can be firm (releasing some grit but still pretty stingy) enough to have some of the best of both actions, and the benefit of staying a bit sharper via faster turnover/renewal rate, but a bit less stable/accurate. And this balance can be good effective. These kinds of synthetic stones in their strides are probably the best for a practical balance between speed and work and accuracy, when they are tuned right for your needs.
As for the other stuff, I know the ark stone will not be able to work on any steel; and there will be a practical limit. I think curving the stone will increase this band. So now, what kind of edge bevels are we now able to do with these other materials. I think the hardness of the steel is a major factor, itself. I have a chisel made from a file. That file has the original temper. I do not sharpen it on the ark. I don't know if it would work, but it surely won't work well. I can tell by the way it feels, that it is struggling with even a fairly narrow edge bevel. (It was very slow to grind that bevel in on an aluminum oxide belt sander, too.)
I still don't know for myself that it can't be effective on "super steels," though. I have no doubt that anything with a very high hardness is not going to fare well. I know some things you said might be super high rc, but maybe others are "super steels" for other reasons? So if you suggest SV30? I might give that a shot. I wouldn't be too sure that these carbides will make that much difference aside from the total percentage increase, I think. The chromium and chromium carbides is a big part of what makes stainless so slow to grind, because that's 13% of the steel. It's a lot. The other stuff is just couple more slightly harder peanuts added to the whole can of chunky peanut butter. Maybe?
So I honestly edited the post you are responding to BEFORE I read the above post of yours just now. Just wanted you to read it, and for other people to know what I added, and that nothing was changed to purposely shade your latest post. I hadn't even read it, yet. So this makes your post look weird, and it makes me look triply redundant, now, but I don't know better to to fix it.
added 2:18:I had also softened some of my language which might have initially been more provocative. I am not looking for any kind of trouble. This asterisked section has, in my own hindsight, become somewhat of a distillation of many of my ideas, and I was trying to flesh it out, a bit. And to streamline it. And to make it more accessible and as not-confrontational as I could, while keeping to my train of thought. This is why I had edited it, in the first place, just for whoever few people might read it for the first time (or again). I didn't know this would have happened.
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Imagine for just one second, a 2" wide single bevel plane blade on a perfectly flattened non-lapping stone in a sharpening guide. How much area of steel to stone do you have? It's huge! How do you expect this kind of abrasive to work like this, at all? This is like taking a file and laying it flat on your welding table, sliding it back and forth, and expecting it to cut even this soft hot rolled steel when using it in this way. This is similar to having too high a TPI for a cut. The file is harder than the steel, but the geometry doesn't work. Take a flat sanding block with some wet/dry sandpaper, and even better add some oil, and this will cut.* THIS is probably why some people claim that ark can't sharpen A2 plane blades, even. But some people can. We tend to think it's the "quality" of the individual stone. But maybe it's more likely the technique. These A2 "upsell/upgrade" blades also tend to be 50% thicker; this is 50% more bevel surface area.
If you think of the soft ark as a very fine toothed file, and you know how to use a file, you might get more out of it. Because it's excellent when used in this way. The finer the file, the smaller the area it can cut. So even after convexing it, there's a limit to what it can handle. But in this case, for most western tools anyway, it can still cut enough to be a sharpening tool, IME.
*Does this mean the file is a bad tool for hogging unhardened steel? No. It's the best unpowered tool in the world for removing material from steel chucked in a vice, when that area of removal isn't thicker than what the file will handle. Way better and faster (and more accurate and controllable) and more efficient than sand paper over a sanding block. We still use files because they are the best at what they do, not to save on sandpaper. Context matters. The sloth is way faster than the barracuda when you put them both on land.
added: Now if you rub that file on your welding table long enough, there are no shavings, still. But maybe you notice it starts to get shiny? Do you say "wow, now THIS is what the file is for! This is the best and only correct way to use a file! This is great! Files are for burnishing!"
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edited:
Regarding the supersteel/SV30?
So ideally, I would want to try a steel which is chock full of these vitamins C and V and w/e other chunks you like in there, but which is not going to be heat-treated as hard a file? I'm thinking 63-65 tops? But the lower, the better.*
Ours is a completely different appreciation of sharpening, BTW. I want the process to be sweet, but also short. All jokes aside.
So I'm looking forwards to the critique from a machinist. If I got something wrong here, I will grateful to know where I've tripped up.
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*Looking at the price of these things, my enthusiasm for this experiment has wained just a little. So if you can suggest the exact brand and model you have the experience and hopefully still have, so i can have the same apple as your apple, that would be nice. And now I see it is S30V, not SV30. Oops.
** edit: Imagine if you had to cut this 4" round of mild steel using only your horizontal saw and you have only an endless and free stack of these 40 tpi blades. But the world depends on this. So you would eventually cut through this steel with this saw. And the way you'd do it is to stop and rotate this round in the vice every several seconds, at first, to target the next high spot where you can get your foot in the door, again. You would be cutting small sections of chords approximating a radius or a curve. Just nibbling off the high spots as you go off that wheel of cheese. At first this will be really slow going. But as you get closer to the center, and that radius decreases, you can cut longer between adjustments. (Because the polygon's # sides of fixed chord length, the length where the saw stalls, is decreasing; the angles of the polygon are decreasing, and the rate at which the cut thickness increases with the depth will decrease.) But I digress. When sharpening, we can't curve some of our edges away from the stone by nibbling it into a radius, because some of these edges need to be straight. We con convex the bevels in order to reduce the cutting area. Compound bevels, same idea. But there a major multiplication of surface area to stone when we put any straight blade onto the flat stone. So we can curve the stone away from the bevel.
To most people of our era, that would sound stupid. If you leave it flat, the stone will just burnish more and "act like a finer grit," right? But it's a fundamentally different tool. You can't put on or even maintain a good edge when you're burnishing too much. Even if you do it longer, you will make an apex, but that edge will not be as hard; this is where you can cut some of that schmoo off with a microbevel, and hope to get to the crunchy center. But if you want to learn it, you can get a better edge than that off the soft, directly, and to sharpen very quickly. Not just finish. Or course if you want the burnishing at the end, you would go to a different stone for that.
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