Sharpening; perpendicular or parallel to the edge, what are the different aspects?

[Fred.Rowe]

What takes place during these two sharpening approaches; one at right angles to the edge the other running parallel to the edge. One removes material along the length of the edge, the other removes material across the edge. What are the pros and cons of each technique? Is one more destructive than the other? Why?
I've studied this a bit but would like to know what others think along these lines.

Happy 2014 forumites, Fred

How do I remove the ad from this post? I don't know if everyone can see the Brownells ad to the right or not. I contacted the mods about this. I hate this crap.

Thanks for deleting this mods, :thumbup:

 

[kwazyjuice]

Hmm... Not sure... I'm a freehanding novice. But from my readings/findings/experiences I thought the proper method was perpendicular to the edge.

I am interested!

 

[Fred.Rowe]

Hmm... Not sure... I'm a freehanding novice. But from my readings/findings/experiences I thought the proper method was perpendicular to the edge.

I am interested!

I believe there may be a preferred method but I don't think proper would apply. What is each technique accomplishing besides bringing the edge to an apex?

 

[me2]

The scratches in the edge run in either perpendicular or parallel, depending on method. For high polish edges, I don't think it matters much. However, for coarse edges, it seems to me that scratches running parallel to the edge would weaken it or allow it to chip easier. Also, the scratches that make the "microteeth" in a coarse edge wouldn't intersect the edge if sharpened parallel, thereby eliminating the advantage of a coarse edge.

 

[kwazyjuice]

It is removing steel from the edge. Making a scratch pattern which would be different from each other using the two techniques. Refining the edge

 

[Skimo]

Both remove steel, both will form a burr, I don't think either is any more destructive than the other, though at lower grits I think sharpening parallel to the blade may result in a weaker edge.

 

[Fred.Rowe]

Is it the scratches that make up the "micro teeth" or is it the fact that one technique produces a "wire edge" while the other does not? With the production of a wire edge along with the removal of said wire edge, comes the "toothy" edge. A wire edge is rarely the result of parallel abrasion; parallel abrasion is usually done in pairs, one on each side of the edge which does not allow a "wire edge" to be produced.

 

[Jason B.]

A wire edge is a edge with a solid and large burr. This only occurres when you have ground past the apex excessively producing a small stiff "wire" at the edge apex.

Edge aggression can be defined by the coarsness of the media used to sharpen. The "teeth" are the result of peaks and valleys created on the edge. A burr or wire on the edge makes the edge incomplete and is technically in a "unfinished" state.

As for the main question, I share similar thoughts as me2.

 

[bpeezer]

Is it the scratches that make up the "micro teeth" or is it the fact that one technique produces a "wire edge" while the other does not? With the production of a wire edge along with the removal of said wire edge, comes the "toothy" edge. A wire edge is rarely the result of parallel abrasion; parallel abrasion is usually done in pairs, one on each side of the edge which does not allow a "wire edge" to be produced.

I'm far from an expert on the subject, but when looking at coarser edges under a microscope it appears that the scratches continue all the way to the edge, yielding the toothy feel. At maximum of 400x magnification (and realistically probably less than that) it's hard to say for sure, hopefully HH will share some thoughts since I believe he has access to a much higher magnification scope.

 

[BluntCut MetalWorks]

Is it the scratches that make up the "micro teeth" or is it the fact that one technique produces a "wire edge" while the other does not? With the production of a wire edge along with the removal of said wire edge, comes the "toothy" edge. A wire edge is rarely the result of parallel abrasion; parallel abrasion is usually done in pairs, one on each side of the edge which does not allow a "wire edge" to be produced.

IM2CO. Using a mid-alloy blade & SiC or Alox abrasive. Abrading perpendicularly more conducive to surface steering abrasion leading to tear at the apex -> i.e. toothy. Parallel abrading vector will most likely either carbide pull/popout or occlude at the apex -> with a lot of popout, might get sharp apex mostly consist of steel matrix; too much occluded, the apex radius won't be smaller than carbide-size. wire-edge can occurs for both approach. note - parallel approach where device (e.g. ERU, V scrapper) has bottom limiter, will certainly minimize burr & wire-edge.

 

[james terrio]

Is it the scratches that make up the "micro teeth"

Of course scratches are a huge factor, this has been proven time and time again with fairly simple micro-photography. More often than not, we can see those scratches and "teeth" with a simple loupe.

Until we get to using an abrasive with a grit finer than the larger carbides in the steel, the "stone" will determine the toothiness to a very large degree.

There are exceptions, of course... D2 is a prime example of steel with very large clumps of chromium carbides, and it will remain "toothy" and uneven almost regardless of how fine an abrasive we use, unless that abrasive is notably harder and has a "grit" smaller than the carbides themselves. (very fine diamond plates or ceramic "stones"). Even at that point, we quickly come back to issues of wearing away the steel matrix itself, while leaving the carbides standing proud.

Sharpening such a steel to a very high degree of keenness is commonly referred to as "a real PITA"

In much finer-grained, low-carbide steels such as AEB-L and 52100, it's actually pretty unusual for the average person to get their hands on a sharpening "stone" with a grit that's finer than the very tight martensite structure and minimal, tiny carbides in the steel itself... so the abrasive medium has even more effect on the fine geometry of the edge (coarseness, toothiness, fineness, etc). Large carbides are simply not part of the equation, and the steel is nearly homogenous in structure, so the edge will be even more consistently determined by the abrasive used to sharpen it.

Likewise, O1 and 1095 are rightfully famous for taking a very keen, crisp edge without much work.

Even so, there will indeed be micro-teeth, inherent in the structure of the steel itself, no matter how fine a "stone" we use. But we're talking sub-micron stuff here, the intersteces of the martensite structure. These tiny imperfections to the plane of the edge rarely have any real noticeable impact on sharpness as far as we can measure, even with CATRA tests and the like.



I cannot think of a reason to sharpen a blade parallel to the edge. I see no benefit to it at all.

While I have not attempted it, I tend to think along the lines (ho ho) of what me2 said, that it would only introduce small stress risers that would do nothing to increase performance, but rather make it more likely for the edge to chip or fall over. I also suspect that bluntcut is right, in that it would result in more tear-out and certainly a less-refined apex.

Pull-through type sharpeners are probably not a good test for this theory, as they tend to be absolutely awful at establishing a nice even bevel. To really test the theory, I suppose one would have to sharpen parallel to edge with "normal" stones. Again... I cannot think of a reason to do so.

I can think of reasons to hone a blade more nearly parallel to the edge, as with a honing steel - to refine a burr or re-align tiny rollovers and microteeth. As has been done with thin, fine-edged kitchen knives for a very long time.

 

[Fred.Rowe]

I cannot think of a reason to sharpen a blade parallel to the edge. I see no benefit to it at all.

Some good points James; but the above is, of course, pursuant to the need, situation and the equipment available. I have a friend who works as a linesman and keeps his knives honed using the large round ceramic insulators that he replaces in transformers; they are laying about in the back of his service vehicle. Sometimes one might not be in the "man cave" or lair and must use what is at hand.

 

[BluntCut MetalWorks]

Some good points James; but the above is, of course, pursuant to the need, situation and the equipment available. I have a friend who works as a linesman and keeps his knives honed using the large round ceramic insulators that he replaces in transformers; they are laying about in the back of his service vehicle. Sometimes one might not be in the "man cave" or lair and must use what is at hand.

I usually finish with violin edge-lead strokes (almost parallel) on the last stone. Reasons for violin (excluding edge-lead aspect): 1st increase effective/higher grit; 2nd lower the pressure without changing downward pressure; 3rd stiffen the apex (hence less rounding); 4th burnish/smooth out vertical scratches on bevel (sort of doing a tilt '+' scratch pattern).

 

[HeavyHanded]

For the most part I agree with Me2 as well. At coarser grit it sets up weak spots that are liable to chip out from the abrasive undercutting the apex to some extent. Also makes it very difficult to distinguish between burr formation and scratch pattern and this relates back to the first observation. At higher levels of polish it matters less and less. The scratch pattern does create cutting characteristics, at least initially, so the rake of the "teeth" relative to the cutting edge makes a big difference in how it will engage materials. I try to shoot for a 45 degree rake into the cutting path and this gives me somewhat smoother cutting edge when I push forward and down, and a more aggressive cut when drawn. As the rake becomes more shallow it begins to loose draw efficiency and push cut better, as it sweeps back toward a 90 it becomes more neutral - all other things being equal.

If we're discussing this as it relates to a carbide scraper, the edge itself might have a number of irregularities just from the abrading mechanism, which by most accounts is not a field of abrasive particles like most grinding surfaces. Might not create a classic scratch pattern but is certainly abrading steel as well as burnishing. I have no experience with this type of sharpening action, even with a cheap model - almost bought one last week to play with but couldn't bring myself to part with the $7. Tough to predict how it might cut but easy enough to compare with a handful of edges sharpened at different rake angles. Would also be somewhat helpful to see the edge backlit at high magnification.

Martin

 

[Fred.Rowe]

I usually finish with violin edge-lead strokes (almost parallel) on the last stone. Reasons for violin (excluding edge-lead aspect): 1st increase effective/higher grit; 2nd lower the pressure without changing downward pressure; 3rd stiffen the apex (hence less rounding); 4th burnish/smooth out vertical scratches on bevel (sort of doing a tilt '+' scratch pattern).

That seems like a good technique; almost like crosshatching the edge. It seem like it would benefit the edge by making the "texture" of the edge more even. I find there are many small imperfections along the length of an edge. They might be very small, unnoticeable almost; but there are hills and valleys to contend with. These small runnels are easily magnified by using the wrong abrading surface or using bad technique. I believe what you are suggesting would have a tendency to smooth these uneven areas out. My ERU sharpener does a good job of "truing" an edge that has these small miss alignments along its length. In my case its because the edge is supported along the length of the abrasive which measures .25 inches. So many of the V sharpeners on the market have so little contact area that is geometrically aligned. With the use of round abrasive rods they tend to magnify the unevenness rather than straightening it. Any V type sharpener with an edge that is canted to where it digs or plows along the edge is a peril to any cutting edge. I'll try your technique the next time I do some freehand. Fred

 

[Fred.Rowe]

For the most part I agree with Me2 as well. At coarser grit it sets up weak spots that are liable to chip out from the abrasive undercutting the apex to some extent. Also makes it very difficult to distinguish between burr formation and scratch pattern and this relates back to the first observation. At higher levels of polish it matters less and less. The scratch pattern does create cutting characteristics, at least initially, so the rake of the "teeth" relative to the cutting edge makes a big difference in how it will engage materials. I try to shoot for a 45 degree rake into the cutting path and this gives me somewhat smoother cutting edge when I push forward and down, and a more aggressive cut when drawn. As the rake becomes more shallow it begins to loose draw efficiency and push cut better, as it sweeps back toward a 90 it becomes more neutral - all other things being equal.

If we're discussing this as it relates to a carbide scraper, the edge itself might have a number of irregularities just from the abrading mechanism, which by most accounts is not a field of abrasive particles like most grinding surfaces. Might not create a classic scratch pattern but is certainly abrading steel as well as burnishing. I have no experience with this type of sharpening action, even with a cheap model - almost bought one last week to play with but couldn't bring myself to part with the $7. Tough to predict how it might cut but easy enough to compare with a handful of edges sharpened at different rake angles. Would also be somewhat helpful to see the edge backlit at high magnification.

Martin

Martin,

In the case of the V style sharpeners the more aggressive the grit the greater the risk of the edge being compromised I agree. But I think thats probable the case with higher grits in general. When I sharpen using a range of belts on the 2 x 72 its when I'm working at 120 grit is where the real damage can be done. The same applies to a perpendicular abrasion; the depth of the scratch is the worry; in this case its running in the opposite direction from the parallel abrasion.
I wish you had signed up for the passaround on the ERU, not looking for your endorsement, but you would have had the experience of using a V style sharpener that works and without damage to the edge. I'm in for the long hall and I know you will get the opportunity at some time.

 

[HeavyHanded]

Martin,

In the case of the V style sharpeners the more aggressive the grit the greater the risk of the edge being compromised I agree. But I think thats probable the case with higher grits in general. When I sharpen using a range of belts on the 2 x 72 its when I'm working at 120 grit is where the real damage can be done. The same applies to a perpendicular abrasion; the depth of the scratch is the worry; in this case its running in the opposite direction from the parallel abrasion.
I wish you had signed up for the passaround on the ERU, not looking for your endorsement, but you would have had the experience of using a V style sharpener that works and without damage to the edge. I'm in for the long hall and I know you will get the opportunity at some time.

Fred, if I had less going on about now I might have signed up for the pass-around, but I felt someone testing it out should have some knowledge of carbide pull throughs as a base line. I've never used one. Will pick up a cheap one and see how it works - complete with micrographs!

Martin

 

[benharpo]

I now use parallel grinding and am a firm believer in its merits. I had only encountered perpendicular grinding before I went to central america and watched the guys there sharpen their machetes parallel to the edge. Those machetes take lots of heavy use, and the guys who use them can't waste money. So if chipping was a huge problem they wouldn't be doing it. Here are the reasons why parallel grinding is better:

1. Easier to form a convex edge
2. Easier to follow curved blades, especially when curvature changes near the tip
3. Easier to work with very long blades
4. Toothiness is not always better
5. Faster

I sharpen knives using silicon carbide sandpaper folded around a piece of glass. I work up through grits 220, 320, 400, 600 ... usually that is enough for me but readily available sandpaper goes up to 3000 grit. Sometimes I'll grind at 45 degrees just before I switch to the next grit, that way I can see when I've polished out the scratches of the previous grit. I vary the blade angle a little bit randomly with each pass this way I polish the entire convex blade. The most difficult thing with other grinding methods is getting the blade angle exactly right, especially if there is a change in curvature. My method is totally forgiving of blade angle.
I sharpen axes and machetes similarly except I only use a file and a coarse stone. Chipping is not a problem.

Serrated blades and saws are sometimes better, but not always. Disposable razor blades would be toothy if that was always advantageous for slicing. It isn't. For chopping, serrated blades are inferior. Because more surface area of the blade makes contact with the material being cut. If there are scratches perpendicular to the edge, that increases surface area.

I am trying to create a perfect polished convex blade. In practice I'm creating an N-compound bevel blade with some scratches parallel to the edge which do not directly contact the material being cut. Spending more time with the finer grades, and honing, get closer to the ideal. But, in practice I don't find that the parallel scratches make a huge difference. Tools that get used heavily tend to get sharpened more frequently with a coarse grind.

I have an austrian scythe which came with its own whetstone and instruction manual. It has its own ovoid sharpening stone which rides along a chine opposite the edge. This creates a hollow ground on what is already a very thin blade. I have chipped it. I'm tempted to change something to get a chisel or convex blade. But, for now I'm sticking to the instructions. Efficient scything requires resharpening approximately every 5 minutes. Parallel strokes are very fast and efficient. In fact a perpendicular grind would not work at all for the blade geometry of a scythe.

 

[bpeezer]

Here are the reasons why parallel grinding is better:

1. Easier to form a convex edge
2. Easier to follow curved blades, especially when curvature changes near the tip
3. Easier to work with very long blades
4. Toothiness is not always better
5. Faster

I don't think those points necessarily make parallel "better" than perpendicular or oblique to the edge. They make parallel cheaper/faster to produce than the alternative for people that need to sharpen frequently in the field. I can't speak for anyone else, but I personally care more about cutting characteristics than sharpening speed. For me, sharpening at an oblique angle consistently provides better cutting characteristics than sharpening parallel to the edge.

 

[davek14]

This is a great subject which I am finding interesting. I usually use fairly simple steels for various reasons and like carbon steel a lot. Many of us became a bit more manic in our knife interests once we "learned to sharpen" myself included. As is usually the case, the more I learn the more I realize how little I know.

I usually begin sharpening (emery cloth double side taped to a plate) parallel to the edge. I'd seen others do it and it's about the only way for me to keep a fairly consistent angle on the curves.

Once I have an edge established I will go to perpendicular with the finer grits. Since the only valid reason to do this always with simpler steels seems to be the direction of the scratches, and since it doesn't matter if you go to a fine grit... s'all good.

But, I do have some knives in D2, 440C, and others. The only thought which seems to contradict my method in these cases is the notorious carbide pull out.

So, I'll follow this thread I think.

Thoughts?