Sharpness

[Trout Hound]

Hi Everybody,
Okay, so, I'm not new to sharpening; I've been doing it for many years now. While I am always able to get my knives acceptably sharp for their intended tasks, I'll admit that I'm not always able to get them totally hair-popping sharp. I got a knife back from the Buck spa recently, and the edge they put on it shaved a patch on my arm completely bald in just a few strokes. This got me to wondering.

For example, I just did some sharpening on my wife's Schrade Old Timer 104OT. It's a USA model, but I honestly can't tell if it's high carbon steel, or one of the ones where they subbed in stainless. I sharpened it using SiC paper on plate glass (adhered with 3M spray), and my process was as follows:

1. Destress edge with a few light slices on 220 grit paper.
2. Profile edge on 220x, using oak wedge guides that I made to maintain 15 DPS. Use 220x until edge no longer reflects light.
3. I then went through 320, 400, and ended with 600x. I was careful throughout the entire process to maintain light pressure.

I spent quite awhile with the 600x, going through several new strips of paper. Still, while the edge feels sharp, it will not pop hairs off my arm like that Buck did, nor will it slice through newsprint like it is thin air.

I chose 15 DPS because, being an EDC pocket knife, I want good edge retention through moderately rough cutting tasks. I also chose to stop at 600x because I prefer some tooth in the edge for EDC tasks.

So, I said all that to say this: For certain steels, at an angle like 15 DPS, and a grit like 600, is it unrealistic for me to expect that level of sharpness? Or, is there something about my process that is preventing me from getting my blades as sharp as they could be?

Thanks a lot for your input!

 

[Dean51]

Take it one step further to 1500x, see if that doesn't help.

 

[me2]

600 grit should shave pretty easily.

 

[Trout Hound]

Okay, an update. For experimentation sake, I pulled out some 1000x paper, and finished it on a ceramic rod. It will now definitely shave hair, although it doesn't "catch" the hair the way the other knife does. It still won't slice newsprint cleanly. I cannot feel any burr along the edge, and the edge does not reflect any light. I can run my fingernail down the length of it smoothly without it catching. All this leads me to believe that I have a clean apex with no wire edge to speak of, and that additional sharpness could only be gained through further edge finishing with finer grit abrasives. Am I correct in my thinking about this? Thanks.

 

[Dean51]

Next step would be 1500x and again you will notice a difference.
The next step after that would be to strop with Bark river compound. I believe the grey is 3000x and the green is 6000x.

 

[HeavyHanded]

Keep in mind on sandpaper you will loose a degree or two per side as the paper compresses (more or less depending on the paper and how much force is applied), putting you at low to mid 30s inclusive. Pretty sure Buck uses a sub 30 inclusive after their BuckEdge 2000 transition. In general 30* inclusive is a pretty solid bet for most steels etc.

You could try stropping on plain paper after the 600 grit with the paper wrapped around a hard surface- it should shave arm hair and crosscut newsprint, though might be a little noisy and hitch a bit as it goes.

 

[Obsessed with Edges]

Okay, an update. For experimentation sake, I pulled out some 1000x paper, and finished it on a ceramic rod. It will now definitely shave hair, although it doesn't "catch" the hair the way the other knife does. It still won't slice newsprint cleanly. I cannot feel any burr along the edge, and the edge does not reflect any light. I can run my fingernail down the length of it smoothly without it catching. All this leads me to believe that I have a clean apex with no wire edge to speak of, and that additional sharpness could only be gained through further edge finishing with finer grit abrasives. Am I correct in my thinking about this? Thanks.

The cutting behavior in paper still indicates a burr, and perhaps an incomplete apex along some portions of the cutting edge. The burr is likely angled or slightly rolled to one side or the other (they almost always are), and it'll shave hair on the side to which it's leaning. The snagging or slipping in newsprint is the indication that the burr is still there, and it's catching the fibers of the paper or getting further folded over and slipping. It can be extremely small, but still enough to get in the way. Past a certain point, the visual or fingernail 'tests' to find the burr will become unreliable, and the cutting is the one thing that'll always tell if the edge is cleanly apexed and burr-free.

An edge can be hair-popping or shaving-sharp at virtually any finish from 150-grit and up. Many 'factory' edges are finished at that level (with some adequate de-burring after), and are still capable of shaving and paper-slicing; this is because the apex is crisp with no burrs and the geometry is consistent. The two most common things getting in the way will be edge-rounding due to inconsistent angle control or too much pressure on conformable backing, or edge geometry that's just too wide to cut well. Going higher in edge finish will only make edge-rounding worse, if the held angle is inconsistent or if the sharpening substrate is too soft (edge becomes rounded AND more polished at the same time).

Focus on getting the edge as sharp as possible at your lowest grit (in this case, 220), and don't move beyond that step until it can at least slice paper cleanly (some small burrs will still likely be there, but small enough to not be much of a problem). Consistent angle control and very light pressure will make the most difference there. Once you've done that, then very, very carefully start working on refinement, checking the edge condition every 2 or 3 strokes to make sure cutting performance isn't degrading, but instead improving (smoother, quieter).


David

 

[Trout Hound]

David, thanks! That helps a lot. I am going to pull out another knife I don't mind practicing on and stick with 220 for awhile until I've got the hang of it.

 

[Obsessed with Edges]

David, thanks! That helps a lot. I am going to pull out another knife I don't mind practicing on and stick with 220 for awhile until I've got the hang of it.

I'd also strongly suggest going as FIRM as possible with the backing under your sandpaper; softer backing is the enemy of crisp edges. I harp on that all the time, and probably sound like a broken record to some, but it'll really help to make your edges as crisp as they can be, even at coarse grit. Really an eye-opener, when you finally realize the difference it can make. :thumbup:


David

 

[Ryan J]

What do you mean by destressing the edge by slicing the paper? I've not heard this term.

 

[Sadden]

Just because the edge no longer reflects light does not mean that you reached the edge of the edge. Go back to 220 and form a burr...

 

[Trout Hound]

What do you mean by destressing the edge by slicing the paper? I've not heard this term.

Learned it from some some Cliff Stamp videos. He says it helps get rid of any wire edge or small nicks/flat spots to begin with.

 

[Obsessed with Edges]

What do you mean by destressing the edge by slicing the paper? I've not heard this term.

This is sometimes done to scrub away 'stressed' (weakened) steel from the edge, before attempting to refine or re-sharpen it; presumably to ensure strong & stable steel is the only thing remaining at the edge. The steel at the apex can sometimes be weakened in use, or in too-aggressive sharpening (heavy pressure, heat damage, etc). The common method is to 'slice into' a stone or other sharpening media, as if attempting to cut it, which should scrub off the weakest remnants from the existing edge. Otherwise, any weakened steel left behind may not hold up well in use, after re-sharpening or refinement.


David

 

[midnight flyer]

An edge can be hair-popping or shaving-sharp at virtually any finish from 150-grit and up. Many 'factory' edges are finished at that level (with some adequate de-burring after), and are still capable of shaving and paper-slicing; this is because the apex is crisp with no burrs and the geometry is consistent. The two most common things getting in the way will be edge-rounding due to inconsistent angle control or too much pressure on conformable backing, or edge geometry that's just too wide to cut well. Going higher in edge finish will only make edge-rounding worse, if the held angle is inconsistent or if the sharpening substrate is too soft (edge becomes rounded AND more polished at the same time).

David

This the exact reason that I always tell my amigos to get a guided system. For me, I have been free hand sharpening for over 50 years, so learning to sharpen to my standards of sharp was the culmination of of years of practice (and frustration!). I was sharpening all my friend's knives before hunting season, and as favors off and on for years and frankly, just got tired of it.

Going to a guided system addresses all the great points David makes. Regardless of your skill level, if you freehand sharpen, you will have an imperfect, convex edge. This is because you are not a machine. But with a guided system you can accurately set the edge angle you want, and replicate it on both sides of the blade with ease, and even polish your edge. If you are successful with a guided system (most are) then you will cut as much as years off your learning curve.

I also appreciate David's comment on being able to shave with lower grits. Back in the 60s through the 80s, I never sharpened to 100,000 grit, yet with our primitive stones such as Arkansas "hard", Washita "soft", and even 600 gr wet and dry sandpaper, I was able to get shaving sharp edges. To this day, my large work knives rarely get edged finer than 600gr.

Before agonizing over the fact your edges aren't as sharp as those touted here, you should recognize that not all steels respond to super fine edges the same, and very few will hold the molecule splitting edges they have. Even my S110V at 60 - 61 Rockwell (Kershaw special edition Shallot) won't hold a hair splitting edge when up against kiln dried white oak I fine tune when hanging doors. And the finer the edge, the easier it is to damage; so the super thin, fine edged knives you read about here are dandy when only used as slicers, but their edges don't last long for the full gamut of duties they have for daily use in my tool belt.

With that in mind, my knives are sharpened differently depending on their steel and use. For example, on my favorite stockman, the large clip blade is sharpened up to 400 grit for a slightly toothy edge that lasts well. The other two blades are sharpened to 1200 grit, and the one I use to cut my cigars is stropped to a mirror polish. My large work knives that do all manner of jobs are sharpened to 600 grit. Once slightly dull, a couple of swipes on my diamond rods have it 100% in seconds. But my chef's knives I use in the kitchen have nice thin edges and they are sharpened to 1200 grit, and touched up every single time I use them on a diamond rod.

If you buy a guided system, even an inexpensive model, you can not only set your edges but you will find that once set they are really easy to maintain. Then when you need to re-set them, it is a snap.

Good luck! Keep practicing and working on your skills and you'll get it.

Robert

 

[lonestar1979]

Most people do not form a burr with the lowest grit, and they just get polished but not sharp edge.Grind away more metal at lower angle and low grit,then raise angle and take off the burr.Knife should shave hair like nothing.

 

[bgentry]

Burr versus No-Burr sharpening is interesting to me. With burr sharpening, you have an affirmative sign that you have apexed the edge. When the burr is formed on the entire edge, you can be sure that you reached the edge of the edge. But then you need to use somewhat different and "special" techniques to make sure you remove every trace of the burr, and not create more burr in the process. In fact, I'd say deburring is one of the top problems for people who post here asking for help. It's a tried and true process, but it's not exactly straightforward. There are a lot of things that are difficult to describe with words that are necessary to really deburr well.

No-Burr sharpening is something I've only done a few experiments with. The idea is to apex the edge and never form a burr at all, or form as small a burr as possible, mostly as an accident. The point is to get to the edge and not form any significant burr, thus obviating the need for "special" burr removal techniques. Which is great when it works.

Using reflected light as an indicator of having apexed the edge gets you pretty close. But how close? Once it won't reflect light any more, the edge is pretty thin. I think CS says it's down to around 20 microns wide when you can no longer see the reflection. ...and how do you know how much further to go once you can no longer see light reflected back from the edge? In my experiments I just kept going, with single back and forth strokes, for some small number of strokes until I thought I was there. I think I also formed small burrs in the process, which I could feel (it's been a while since my experiments). CS says you can start to judge this based on experience, but then we're back to the "hard to describe" murky waters again.

With my Yojimbo 2, sharpened up to DMT EF using the No-Burr method, I got an edge that cross cut phonebook paper with no hangs, and popped hair from my leg pretty well. I was actually quite impressed. But Wharncliffe blades are easy, so I did have that going for me.

I'm glad the OP posted this to remind me of this alternate method.

Brian.

 

[Trout Hound]

Thank you everyone, especially David, aka Obsessed with Edges, for helping me fix my stupid self. Here's where I am in the last few hours: I went back to 220 as suggested until I could slice newsprint, then carefully worked my way back up to 600. I also removed the squishy rubber rug mat that I had under the plate glass, because, being a genius, I put it there to keep the glass in place, not considering the effect it might have on the sharpening process. I am now definitely in the newsprint slicing business. It won't push cut through the edge of the paper, but it will initiate a clean, slicing cut, perpendicular to the paper edge, without tearing. Interestingly enough, now it doesn't shave as well as it did before, but I hope the paper cutting is at least a sign that I have a pretty clean apex now. Yes?

 

[Obsessed with Edges]

Thank you everyone, especially David, aka Obsessed with Edges, for helping me fix my stupid self. Here's where I am in the last few hours: I went back to 220 as suggested until I could slice newsprint, then carefully worked my way back up to 600. I also removed the squishy rubber rug mat that I had under the plate glass, because, being a genius, I put it there to keep the glass in place, not considering the effect it might have on the sharpening process. I am now definitely in the newsprint slicing business. It won't push cut through the edge of the paper, but it will initiate a clean, slicing cut, perpendicular to the paper edge, without tearing. Interestingly enough, now it doesn't shave as well as it did before, but I hope the paper cutting is at least a sign that I have a pretty clean apex now. Yes?

Getting better, for sure. :thumbup:

For shaving, beyond paper-slicing, keep working at thinning & refining the apex (gently) at the same coarse grit, as shaving sharpness isn't far away. Big changes can come in just a few additional passes at ever-decreasing pressure. As the edge becomes finer, it will also become more fragile; this is why it's important to keep lessening pressure as you progress. If/when you begin to see some hairs popping off, you might also start experimenting with some light stropping to see if that'll clean up most of the light burrs remaining. You'll know your edge is highly refined when you see obvious improvement in just a few light passes on the strop (paper-slicing gets smoother, quieter and requiring less effort, and you might see the edge go from 'rough shaving' to 'hair-popping' to 'tree-topping' in just a few passes).

I'd still focus on getting as much out of your coarser grits as you can. As you make progress with that, the refining stages get a LOT easier, and can also take sharpness up an additional notch or two (or three), so long as you don't overdo it with pressure or too many strokes.

BTW, the rubber mat being under your glass plate might not be a big deal. It'd be more of a concern if it was underneath the sandpaper itself, allowing the paper to compress or roll underneath your edge. I can appreciate putting something under the glass plate to keep it from sliding around (I've sometimes used something similar), so I wouldn't worry about that myself. The glass plate I've sometimes used has some small circular rubber 'feet' at the corners, which accomplish the same thing.


David