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

At times, I've experimented with techniques that run essentially parallel to the edge. Mainly I was doing this in searching for a stroke that keeps the angle steadier and more consistent, and it did help with this to a large degree. The downside I noticed, was that it eliminated most of the 'bite' from the edge, even when doing so on a coarse stone. So, if I used the technique at all, I did so only to set bevels or otherwise establish the geometry; then I'd follow up with perpedicular or diagonal strokes to re-establish the grind lines that make up the 'teeth' in the edge.

I'd think there could be circumstances when a parallel stroke on a coarser hone might effectively 'score' the bevels lengthwise, close behind the apex, and possibly weaken or undercut the supporting geometry, leaving it somewhat more prone to folding over or chipping. Maybe not as severe, but this would approach or emulate the sort of damage seen in micrographs of edges sharpened on conventional scissor-edged carbide 'V' pull-through sharpeners, on which lengthy rectangular sections of the edge can be seen chipped out, folded or dangling.

On finer & polishing hones, I'd think a parallel stroke shouldn't do as much harm, if any, if there aren't any deep scratches being formed parallel to and just behind the apex of the edge. I have occasionally used a Fine/UF ceramic hone or hard black Arkansas stone, with a parallel stroke, to clean up burrs or re-align an edge, and it can work pretty well for that.


David
 
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Obsessed with Edges said:
At times, I've experimented with techniques that run essentially parallel to the edge. Mainly I was doing this in searching for a stroke that keeps the angle steadier and more consistent, and it did help with this to a large degree. The downside I noticed, was that it eliminated most of the 'bite' from the edge, even when doing so on a coarse stone. So, if I used the technique at all, I did so only to set bevels or otherwise establish the geometry; then I'd follow up with perpedicular or diagonal strokes to re-establish the grind lines that make up the 'teeth' in the edge.

I'd think there could be circumstances when a parallel stroke on a coarser hone might effectively 'score' the bevels lengthwise, close behind the apex, and possibly weaken or undercut the supporting geometry, leaving it somewhat more prone to folding over or chipping. Maybe not as severe, but this would approach or emulate the sort of damage seen in micrographs of edges sharpened on conventional scissor-edged carbide 'V' pull-through sharpeners, on which lengthy rectangular sections of the edge can be seen chipped out, folded or dangling.

On finer & polishing hones, I'd think a parallel stroke shouldn't do as much harm, if any, if there aren't any deep scratches being formed parallel to and just behind the apex of the edge. I have occasionally used a Fine/UF ceramic hone or hard black Arkansas stone, with a parallel stroke, to clean up burrs or re-align an edge, and it can work pretty well for that.


David
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I wonder if the perpendicular scratches don't also contribute to chipping along an edge. I imagine an edge looking like a hack saw "on it's side" running its length when sharpened at right angles to the edge. Hills and valleys. Of course these would be lessened as finer grits are used. But this is the same when sharpening parallel to the cutting edge. The hills and valleys will be reduced as the abrading material is refined. Which edge failure is more acceptable; parallel along the edge or at right angles to the edge. Since the act of cutting itself is done in line with the cutting edge, "parallel" and not so much in a twisting motion where the edge would be bent or torqued at 90 degrees. I've seen micro-graph photos of damascus blades where different steels have been used and you can really see these hills and valleys when the blade has been sharpened at 90 degrees to the apex. I've found using the ERU "V" sharpener that this lessens this result because running parallel to the edge lessens the removal of the softer steels along the edge of the damascus. The abrasion rides along the tops of the harder material and leaves the softer material in place. Of course we are splitting hairs here :) because the edge is, in its working form a very refined profile without large gouges and hills and valleys. At least thats hopefully the result of sharpening.

Regards, Fred
 
I'm mostly in line with OWE on this one. The biggest issue is going to be undercutting along the edge with a strong second for it being difficult in some cases to distinguish the bur from a parallel scratch trough. I've also seen (and micrographed) images of edge wear on an edge sharpened at a 45* to the grind path, where a small bit of steel or mineral embedded in wood will score the edge a few microns from the apex. It then takes very little to snap the cutting apex right off. A similar condition can arise from other forms of parallel grinding work, something I also saw and recorded and a similar effect described by Verhoeven on his 'steeling' section. In his case, I cannot imagine why he used the steels parallel to the edge, even the old Betty Crocker cookbook states to use a diagonal sliding motion.

At the finer level it will become less of an issue, but now we're talking about a highly refined edge. Also, my work with parallel sharpening via carbide scrapers showed that it was only a real issue when there were largish irregularities in the carbide heads, and if one did not spin the cutters every few passes to minimize the effect from repetitively working a defect into one side of the bevel. If the heads are nicely tooled there should be zero issues. I would still recommend changing sides every few passes just to be safe.
 
Any really deep scratches could possibly contribute to chipping, given the right circumstances. My main concern is, on blades with deeper lengthwise scratches close to the apex, when chips do occur, they often are much bigger (longer), sometimes allowing very long sections to fold or break away along the continuously thin edge, as opposed to the smaller chips that might occur between the 'upright' scratches on an edge sharpened in perpendicular fashion, or individual 'points' fracturing off of the teeth. On such an edge, the 'hilltops' of thicker steel between the deep troughs of the scratch pattern should act to limit the length of the break along the thin edge, and thicker steel above the apex helps to limit how far a chip or fracture might reach vertically into the blade, as opposed to having no such 'end stops' for a lengthwise fracture created by a deep scratch parallel to the edge.

I sort of think of a piece of corrugated cardboard as the 'blade' when envisioning this, with the 'cutting edge' running either parallel to, or perpendicular to the corrugations; I think of the corrugations themselves as representing the hills & valleys of the scratch pattern. If some lateral force is exerted in a plane parallel to the corrugations (if the cutting edge were parallel), the piece will tend to fold more easily along that intersecting plane. If force is exerted in a plane perpendicular to those corrugations (with cutting edge perpendicular to them), the material retains more of it's strength and resists folding. I suppose this model could also be considered using a sheet of glass as the 'blade', and the effect a scored line (applied with a 'glass cutter' tool) has when utilizing it to easily and neatly break the glass along that line, by 'bending' the glass along a plane parallel to it.

^^This is ALL speculative on my part, so keep that in mind. But, that's what comes to mind when I consider what might happen with a lengthwise grind pattern, as opposed to a perpendicular pattern.


David

Fred.Rowe said:
I wonder if the perpendicular scratches don't also contribute to chipping along an edge. I imagine an edge looking like a hack saw "on it's side" running its length when sharpened at right angles to the edge. Hills and valleys. Of course these would be lessened as finer grits are used. But this is the same when sharpening parallel to the cutting edge. The hills and valleys will be reduced as the abrading material is refined. Which edge failure is more acceptable; parallel along the edge or at right angles to the edge. Since the act of cutting itself is done in line with the cutting edge, "parallel" and not so much in a twisting motion where the edge would be bent or torqued at 90 degrees. I've seen micro-graph photos of damascus blades where different steels have been used and you can really see these hills and valleys when the blade has been sharpened at 90 degrees to the apex. I've found using the ERU "V" sharpener that this lessens this result because running parallel to the edge lessens the removal of the softer steels along the edge of the damascus. The abrasion rides along the tops of the harder material and leaves the softer material in place. Of course we are splitting hairs here :) because the edge is, in its working form a very refined profile without large gouges and hills and valleys. At least thats hopefully the result of sharpening.

Regards, Fred
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I use knives in a chopping motion around the shop a good deal, even more so than slicing. Its just the type of work I do. I have damaged edges, as you relate, but instead of parallel to the edge, across the the apex. My shop is full of numerous abrasive material of all kinds and they tend to get embedded in materials I use in the shop. Its easy to damage a fine edge in most any aspect, diagonal, parallel, or directly across the cutting edge. I've come to believe that combining both parallel and perpendicular abrasions is useful. When I use a diamond plate to establish a flat edge I use perpendicular motions along the plate; when I switch to the ERU "V" sharpener to finish the edge I use a parallel abrasion which goes across the scratch pattern left by the work on the diamond plate. This provides an opportunity for me to assess the work I've already done. In this manner it is quite easy to see any "errors" along the edge. Thers no need to apply magic marker along the edge using this technique. Its very similar to finishing a primary bevel when making a knife; you first sand across the bevel and next when you switch grits you sand with the bevel plunge to tip. By doing this you can access the finish on the surface of the bevel.

I posted this before reading your last post David
 
bpeezer said:
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.
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Yes, the main argument for parallel strokes is that it is fast and easy to restore a quality field edge, especially on long curved blades with convex edges. If I spend a few minutes sharpening an axe with just a file, I can get an extremely uniform convex blade. I test that by watching the reflection as I move the axe while holding the light source and my eyes fixed. With parrallel strokes its much more difficult to work out flat spots and ridges and establish a uniform cross section for the entire blade.

As OWE mentioned, a good technique is to use parallel grinding to establish the basic edge geometry, then finish with perpendicular grinding for toothiness and to eliminate potentially weak parallel scratches.

The best example of weakening an edge by sharpening parallel is chainsaw blades. I admit that chainsaw blades with a factory edge hold up quite well. Once I start resharpening with file, I have to keep resharpening almost every hour, because the performance drops pretty fast. They make a machine that sharpens chainsaw blades perpendicular. I wonder if anybody has experience using something like this. http://www.timberlinesharpener.com/

I think the weakness caused by parallel scratching is much more severe in hollow ground edges, and much less of a problem in convex edges.
 
benharpo said:
Yes, the main argument for parallel strokes is that it is fast and easy to restore a quality field edge, especially on long curved blades with convex edges. If I spend a few minutes sharpening an axe with just a file, I can get an extremely uniform convex blade. I test that by watching the reflection as I move the axe while holding the light source and my eyes fixed. With parrallel strokes its much more difficult to work out flat spots and ridges and establish a uniform cross section for the entire blade.

As OWE mentioned, a good technique is to use parallel grinding to establish the basic edge geometry, then finish with perpendicular grinding for toothiness and to eliminate potentially weak parallel scratches.

The best example of weakening an edge by sharpening parallel is chainsaw blades. I admit that chainsaw blades with a factory edge hold up quite well. Once I start resharpening with file, I have to keep resharpening almost every hour, because the performance drops pretty fast. They make a machine that sharpens chainsaw blades perpendicular. I wonder if anybody has experience using something like this. http://www.timberlinesharpener.com/

I think the weakness caused by parallel scratching is much more severe in hollow ground edges, and much less of a problem in convex edges.
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I may be reading your example incorrectly but I believe what your saying should be reversed. Isn't a chainsaw file used perpendicular to the cutting edge, where as the timberline tool is sharpening in a parallel manner? I apologize if I've misinterpreted your comment.
 
benharpo said:
Pushing the file creates scratches parallel to the edge of each tooth.
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I think I'm pointing out the obvious here. I cut wood for thirty years and when you hand sharpen a chain saw tooth the scratches run perpendicular to the cutting edge. The file is being pushed across the cutting edge at 90 degrees. Do you sharpen chain saw chains. If you do take a look at one.

It may be that you are using something different than I am used to.


Fred
 
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Upon reading this topic last night, I had been thinking on it today while touching up my daily carry knife with 425M steel. I was honing it on a early Norton India stone. After working up a burr, I removed it with edge leading stokes, parallel to the stone. Working in another area of the blade I worked up a burr and now removed it with a perpendicular or lateral stoke across the stone. This lite movement removed the burr much quicker than the parallel grinding. (with one & a half strokes) I'll now notice how well this edge lasts. This is merely preliminary but I don't mind trying different methods and note the results. It certainly left a nice sharp edge. DM
 
Fred.Rowe said:
I think I'm pointing out the obvious here. I cut wood for thirty years and when you hand sharpen a chain saw tooth the scratches run perpendicular to the cutting edge. The file is being pushed across the cutting edge at 90 degrees. Do you sharpen chain saw chains. If you do take a look at one.

It may be that you are using something different than I am used to.


Fred
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I don't think the chain saw comparison is valid. I don't know whether one direction is best on knives (I am still thinking and reading about it). I think files are designed to be easy to see and produce quick results on chains. They are designed for guys who are not perfectionists and might not even be fully awake at 5:00am. before cutting. The Dremel does sharpen chains perpendicular to the edge FWIW..
 
wvdavidr said:
I don't think the chain saw comparison is valid. I don't know whether one direction is best on knives (I am still thinking and reading about it). I think files are designed to be easy to see and produce quick results on chains. They are designed for guys who are not perfectionists and might not even be fully awake at 5:00am. before cutting. The Dremel does sharpen chains perpendicular to the edge FWIW..
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Maybe I am looking at this wrong; but it does interest me. This picture is a chainsaw tooth has the cutting edge to the right. Its in the shape of an inverted "L" , with the cutting edge being along the edge of the "L". When sharpening with a file, the file lays across the top of the bar in diagonal position. Ig]t lays flat against the cutting edge in this position and is moved back and forth. Does this not leave scratch lines perpendicular to the cutting edge on the long side of the tooth and diagonally across the flat area of the tooth at the top. When a rotary file is used wont the tool leave parallel scratches across the cutting edge these surfaces? Tell me how you interpret this.

Regards, Fred


P61_2.jpg
 
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A good part of the cutting surface is on the underside of the top leg. You're both correct, the pattern runs parallel (along the underside of the top cutter) and perpendicular ( to the upright portion). Both surfaces cut.

FWIW, I've gotten much better life from my blade once I start sharpening it as long as I set the depth gauge properly for the wood I'm cutting (and anti-kick links if equipped).
 
It could just be the photo but mine (chainsaw) when sharpened leave more metal on top of the tooth. So, it looks like a sharpened notch not a 'L'. Mine are only ground down in the notch and it is a Husqvarna model 455 Rancher. The top of that tooth is flat and rides on the wood the bottom is sharpened. ONe could use a round diamond file to finish the sharpening finer. DM
 
I think of the primary edge as the underside of the top cutter. This part will begin to cut a chip loose before the curved portion makes contact.
 
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670px-Sharpen-a-Chainsaw-Step-1.jpg


The top-plate functions as the horizontal chisel, the side-plate functions as the vertical chisel, and the corner where they meet makes penetration.

Sharpening with a file runs the scratch-pattern perpendicular to the edge on the side-plate and approximately parallel to the edge of the top-plate. As a result, the apex of the top-plate is weakened and folds/fractures/degrades more quickly/easily, resulting in a blade similar to what Fred.Rowe posted, with the side-plate leading the top-plate by a substantial margin :thumbdn:

Sharpening with a dremel allows a finer scratch-pattern and it runs perpendicular to the top-plate's edge improving strength as well as penetration (the 'point' of teeth), reducing wear on the blade and load on the engine. While this method does produce parallel scratches to the side-plate's edge, the scratches are finer and the angle is more easily adjusted to improve durability without substantially compromising performance.

I use a dremel on the chain of my Husky 440e cutting up oak around the property for my winter's heat. The 440e isn't that powerful but is light-weight and with a well-sharpened blade works very efficiently :thumbup:
 
Being a kinetic learner; I had to get my chain saw out and run a file across the teeth to make it clear what is going on. Now its clear. A little off topic but still enlightening for me. Thanks for the discourse gentlemen.

Fred
 
David Martin said:
Upon reading this topic last night, I had been thinking on it today while touching up my daily carry knife with 425M steel. I was honing it on a early Norton India stone. After working up a burr, I removed it with edge leading stokes, parallel to the stone. Working in another area of the blade I worked up a burr and now removed it with a perpendicular or lateral stoke across the stone. This lite movement removed the burr much quicker than the parallel grinding. (with one & a half strokes) I'll now notice how well this edge lasts. This is merely preliminary but I don't mind trying different methods and note the results. It certainly left a nice sharp edge. DM
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I'll be very interested in your results, thanks David!
 
I haven't cut much today with it. Just some cardboard boxes and string but so far all looks well. DM
 
Tonight I had time to cut some cardboard with this knife. After cutting 60 feet of cardboard I inspected the blade using 7.5X magnification. I found a burr had returned in the area that I had removed it using the lateral stroke. The area that the burr was removed using a parallel stroke showed no burr. Now, I'll remove this burr using the parallel stroke. DM
 
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