David Martin
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hard, Do you mean, fine grain means 'lower' than 5 on the scale ? DM
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Coarse edge stropping
- Thread starter HeavyHanded
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Here's another long-winded ramble....
Had a chance to follow up with the 120 grit compound. As I feared it was too large to get down into the grind for good burr removal. Took three times as many passes on the strop to remove the burr, and examination under magnification showed polishing only along the very top of the edge and outermost surfaces of the grind pattern. It might be a possible finisher for stone grits under 50, I'm gonna leave it to someone else how to get that low and still bring both bevels together cleanly.
Continued with the 220 grit to see what the long term effects of stropping would be. After approx 60 passes the scallops began to smooth out around the edges and the ability of the edge to catch on materials was greatly reduced, though it did seem to slightly improve the push cutting. This leads me to partially reconsider some of my basic assumptions. Many people think of a coarse edge as having teeth that catch and tear, and are fairly quickly worn away. My own observations at the fairly acute angels I'm using, is that the coarse edge has low spots where the larger grains have passed through, with most of the edge being relatively flat but weaving back and forth ( viewed at a 45 degree angle it looks more uneven than it does in profile). This leaves behind a small scallop-shaped "serration" that cuts with its edge more so its teeth. Its possible to push cut paper with a very coarse edge and when this happens one can feel and see that the paper gets caught in a low spot and cut much like it would with any fine edge (as long as it stays in its place). The edge looses its ability to cut at this level fairly quickly because the scallop likely had a small burr that can be very tricky to remove effectively, and this wears away. While it may be challenging, there's no reason they can't be made to last every bit as long as a similar length of fine edge, and there are no shortage of people (myself included) who claim to be doing just that. That said, these edges need to be crisp along their entire cutting surface (and in particular the trailing edge), or the quality will suffer.
What teeth there were provide less effective but longer lasting cutting utility. Take a close look at a hard-used coarse edge and you'll see there are still plenty of irregularities, its when the cutting surfaces get dull that it looses a lot of its better cutting characteristics.
Why do some people have such better luck with coarse edges? In addition to differences in steel and grinding media, they are probably getting more of the burr off the scallop than others, with or without a strop, resulting (just like with a fine edge) in a much longer-lasting edge. That's what led me to do this partially successful test with the 220grit compound.
One last observation that I still cannot verify but am growing more convinced of as I did this test, is the importance of the grind angle to getting the most out of a coarse edge both in terms of longevity and initial cutting efficiency. When I say "grind angle" I'm not talking about bevel angle but rather the edge angle relative to the grinding direction. By raking it forward, presenting the angle more directly into the cutting path, the center of the scallops are doing more of the cutting than the trailing edge - what happens if your grind pattern is perpendicular to the edge. Imagine if the serrations on a traditional serrated knife were angled into the draw cut, the wear pattern would be spread over more of the cutting surface. As it is, the lead edge of a serration (and to a lesser extent the center) sees less wear compared to the trailing edge when used with a drawing motion. It would cut more aggressively on a draw, and less so on a straight press or forward pushing cut instead of being neutrally aligned. Consider, on a saw blade the cutting surfaces are so entirely angled into the cutting direction they're virtually unidirectional. With a serrated edge this could cause it to choke on some tougher materials but at the scale of a coarse edge its a benefit, and with a fine edge its largely irrelevant.
That's all, I am officially out of noodling time for the next couple of weeks. Hope this gets some people thinking. I can't stand behind any of this 100%, but these are the conclusions I've drawn based on my limited observations.
HH
Had a chance to follow up with the 120 grit compound. As I feared it was too large to get down into the grind for good burr removal. Took three times as many passes on the strop to remove the burr, and examination under magnification showed polishing only along the very top of the edge and outermost surfaces of the grind pattern. It might be a possible finisher for stone grits under 50, I'm gonna leave it to someone else how to get that low and still bring both bevels together cleanly.
Continued with the 220 grit to see what the long term effects of stropping would be. After approx 60 passes the scallops began to smooth out around the edges and the ability of the edge to catch on materials was greatly reduced, though it did seem to slightly improve the push cutting. This leads me to partially reconsider some of my basic assumptions. Many people think of a coarse edge as having teeth that catch and tear, and are fairly quickly worn away. My own observations at the fairly acute angels I'm using, is that the coarse edge has low spots where the larger grains have passed through, with most of the edge being relatively flat but weaving back and forth ( viewed at a 45 degree angle it looks more uneven than it does in profile). This leaves behind a small scallop-shaped "serration" that cuts with its edge more so its teeth. Its possible to push cut paper with a very coarse edge and when this happens one can feel and see that the paper gets caught in a low spot and cut much like it would with any fine edge (as long as it stays in its place). The edge looses its ability to cut at this level fairly quickly because the scallop likely had a small burr that can be very tricky to remove effectively, and this wears away. While it may be challenging, there's no reason they can't be made to last every bit as long as a similar length of fine edge, and there are no shortage of people (myself included) who claim to be doing just that. That said, these edges need to be crisp along their entire cutting surface (and in particular the trailing edge), or the quality will suffer.
What teeth there were provide less effective but longer lasting cutting utility. Take a close look at a hard-used coarse edge and you'll see there are still plenty of irregularities, its when the cutting surfaces get dull that it looses a lot of its better cutting characteristics.
Why do some people have such better luck with coarse edges? In addition to differences in steel and grinding media, they are probably getting more of the burr off the scallop than others, with or without a strop, resulting (just like with a fine edge) in a much longer-lasting edge. That's what led me to do this partially successful test with the 220grit compound.
One last observation that I still cannot verify but am growing more convinced of as I did this test, is the importance of the grind angle to getting the most out of a coarse edge both in terms of longevity and initial cutting efficiency. When I say "grind angle" I'm not talking about bevel angle but rather the edge angle relative to the grinding direction. By raking it forward, presenting the angle more directly into the cutting path, the center of the scallops are doing more of the cutting than the trailing edge - what happens if your grind pattern is perpendicular to the edge. Imagine if the serrations on a traditional serrated knife were angled into the draw cut, the wear pattern would be spread over more of the cutting surface. As it is, the lead edge of a serration (and to a lesser extent the center) sees less wear compared to the trailing edge when used with a drawing motion. It would cut more aggressively on a draw, and less so on a straight press or forward pushing cut instead of being neutrally aligned. Consider, on a saw blade the cutting surfaces are so entirely angled into the cutting direction they're virtually unidirectional. With a serrated edge this could cause it to choke on some tougher materials but at the scale of a coarse edge its a benefit, and with a fine edge its largely irrelevant.
That's all, I am officially out of noodling time for the next couple of weeks. Hope this gets some people thinking. I can't stand behind any of this 100%, but these are the conclusions I've drawn based on my limited observations.
HH
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If that is actually the case, then the steel and abrasive type would make a HUGE difference in the final edge, as in some cases the abraded teeth would have less of a 'fine' cutting edge on them, and others could have an edge that would grab like crazy, like concertina wire. I guess it would also impact the final edgeholding as well, with the best edgeholding likely somewhere in between.
David Martin
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Not nearly as clearly written/ explained as some other writings . I read it several times over the span of two days and still could not really grasp some of the points . However, try using the muscle side of the leather out as a strop . This tends to get into the micro-serration divots better knocking off those pesky burrs . It worked for me sharpening at 100grit . Still, the technique of the sharpener is a big asset in burr removal when sharpening on coarse stones . As I've read of guys getting great edge retention sharpening their edges coarsely and never even use a strop . Whether we can determine how this is happening in this discussion or not it still remains present . Then I'm positive the type of steel has an effect on this to some degree . DM
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I think this applies to me as well. Prior to this experiment I never used a strop on any of my hard-use knives. As it is, stropping the coarse edge only seemed to help when the inclusive angle was under 30 degrees. As I approach a 40 degree bevel it becomes easier to remove most if not all of the burr using just the stone. I get very good edge retention without a strop, but am still at a loss to explain all the variables - type of steel must play a fairly prominent role (my apologies for the last post, very difficult to clearly explain without lots of photos and I've been spending far too much time staring through a loupe lately).
In any event, I don't think the 220 grit is a very good option for maintenance, but it does do a good job of cleaning up the grind from a 60 and 80 grit stone if done at a fairly acute angle (I now have doubts that this really does improve cutting efficiency for a coarse edge anyway). I did go back and attempt to strop with a more normal compound, and did not get good results. I'll have to try it next with a rougher chunk of leather. As you pointed out earlier, longevity with this type of edge is probably good enough that maintaining it with a stone is already the easiest and most effective method.
HH
David Martin
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Thanks Heavy, this cleared up questions I didn't care to ask . To capture the best of both worlds seems to be ( you put it 'ease of maintenance') sharpening at 17* coarse . Which will give (on some steels) good edge retention and less stone and strop work . In light of this discussion I see the need to do more testing with a coarsely sharpened edge on different steels . What I mean by coarse sharpening is 100grit . I recently tested a blade of 440C and D2 . Both were sharpened at 240grit and ended up cutting / processing the same amount . I was processing chickens and both did 18 before becoming sufficantly dulled that I would have taken them to the stone . Which suprised me as I had read D2 gives great edge retention because of V content . During this discussion it occured to me that D2 steel may realize better edge retention when sharpened at a higher grit . So, I'm going to resharpen the blade of D2 up to 600 grit and cut up some more . If it does only 2-3 more I'm sure 440C could do the same sharpened more coarse at 100 grit . But if it does 6 more I'll admit were on to something with finer grain, non-stainless steels . DM
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Sounds like you have a better testing protocol than I can whip up. It would be extremely interesting to find that the respective metals performed better as the relative differences in grit increased. D2 might prefer closer to 1200 and the 440 at 100? That would make for a very interesting bit of info if it could be extrapolated across more steel types - would also do nothing to quell the controversy re coarse edges but for those interested in this sort of thing...
I almost wonder if a well-versed machinist/engineer could make some guesses as to the outcome just from looking at the tooling specs for each steel variety. A coarse edge would be considered more of a machining operation and a finer edge more of a finishing operation?
HH
I almost wonder if a well-versed machinist/engineer could make some guesses as to the outcome just from looking at the tooling specs for each steel variety. A coarse edge would be considered more of a machining operation and a finer edge more of a finishing operation?
HH
David Martin
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Ok Heavy I'll take D2 up to 1200 grit . No problem ! I got arrogantly rebuttled the last time I did some tests and posted the evidence . Yet, I don't whine about conducting the test though it cost me material and time . As I enjoy learning rather than relying on someone elses opinion . DM
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DM, I went back and read your last retention testing in the Buck subforum - interesting stuff, and pretty much adds more weight to my own sporadic test results. A couple of conclusions I've come to:
Different grinding media can give very different results at the same approximate "grit level". This leads to number two -
Across all the metals, angles and grinds that I have tested, the edge imparted by diamonds seems to be superior at the low to mid grit range. I've never tested the 120 grit DMT, but it sounds like pretty gnarly, maybe I should consider adding one to the crew. The second best, SiC gives very good results too (and possibly better at the lower grits), but for some reason I have to take off more metal following SiC if I want to progress to a finer stone, I can go from diamond or Arkansas with a lot less carry-over metal deformation (hope I'm not becoming incomprehensible again). Its a great choice, esp for the harder metals out there, but only if I'm going to stop at a fine SiC and not move on.
Third, my soft Arkansas is too fine for utility use, and the Washita is pushing it. The upper limit seems to be in the region of a fine diamond stone, Smith's rates theirs at 750. This means I've blown a lot of cash over the years chasing results I didn't want to begin with! Of course, there's only one way to learn this stuff and be able to test it on one's own - you've got jump in.
Fourth, there are so many variables involved that I'm going to have to take a little time off from thinking about this for a while. 325 grit Smith's diamond is getting the nod for awhile till I get a bug up again or DMT sends me a replacement EF stone for the warped one I sent back. After all, it wouldn't be right not to test it...
HH
Different grinding media can give very different results at the same approximate "grit level". This leads to number two -
Across all the metals, angles and grinds that I have tested, the edge imparted by diamonds seems to be superior at the low to mid grit range. I've never tested the 120 grit DMT, but it sounds like pretty gnarly, maybe I should consider adding one to the crew. The second best, SiC gives very good results too (and possibly better at the lower grits), but for some reason I have to take off more metal following SiC if I want to progress to a finer stone, I can go from diamond or Arkansas with a lot less carry-over metal deformation (hope I'm not becoming incomprehensible again). Its a great choice, esp for the harder metals out there, but only if I'm going to stop at a fine SiC and not move on.
Third, my soft Arkansas is too fine for utility use, and the Washita is pushing it. The upper limit seems to be in the region of a fine diamond stone, Smith's rates theirs at 750. This means I've blown a lot of cash over the years chasing results I didn't want to begin with! Of course, there's only one way to learn this stuff and be able to test it on one's own - you've got jump in.
Fourth, there are so many variables involved that I'm going to have to take a little time off from thinking about this for a while. 325 grit Smith's diamond is getting the nod for awhile till I get a bug up again or DMT sends me a replacement EF stone for the warped one I sent back. After all, it wouldn't be right not to test it...
HH
David Martin
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Heavy, Thank you for your kind words . What your seeing is the same conclusions I ran into . That diamond leaves a more toothy edge and holds it longer as some stainless steels like that type edge . Yes, if sharpening w/ diamond 600 grit is max. I'd take an edge and mostly only to coarse (325) or less depending on like you say, general edge use . Again, I agree a Norton coarse/ fine SiC stone offers good value and a very good edge . Perhaps not the 'best' but what does that 'best' cost you ? Then in your last sentence; Yes, alot of variables . I realize I could spend all of 2011 testing various knife steels sharpened coarse and fine . Inorder to nail down some good factual data . (Which I'm actually doing just over more time .) Agreed, "it wouldn't be right not to test it" and all it takes is rolling up your sleeves, sharpening and cutting some . I understood every point . Well, written . DM
David Martin
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Heavy, I think I'll use sisal rope for the above mentioned test . As thats what I have the most of . DM
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There's more to this than can be quickly explained. Verhooven noted the extremely rough edge imparted by SiC in his oft-quoted paper, but the convex and belt sanding operations that produce very good quality edges rely mostly on SiC abrasives not to mention the finishing touches on paper wheel set-ups. There's a big difference in the edge quality using SiC depending on edge-leading or edge-trailing. I've been working on that myself, and have gotten much better edges using a fore and aft technique with a little more pressure on the pull stroke. This seems to give a cleaner edge than strict edge-leading strokes, but leaves me with less of a burr to deal with than strictly edge-trailing.
HH
David Martin
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Heavy, Yes, good point . I should have mentioned that the edges I'm speaking of are ALL brought about from stones . Its a different edge than those from a belt sander . The edges I get from my belt sander are far more refined and compares with using a 200 grit finer stone . Its also faster, easier and has far less burrs . Yes, all my belts are SiC abrasive . Then when you factor in a paper or leather wheel that certainly takes it up another noch or two . So, by using stones and just a hand leather strop I've been trying to keep things on a duplicatable, level, playing field . Dr. Verhoven also mentioned in his findings that the trailing edge sharpening had more debris than the edge leading sharpening . So, your findings seem to be different . DM
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Let me clarify a little. I find exactly what Verhooven did re edge trailing and burr formation, but like you and many others, I also noticed that my belt sanding imparts a very nice edge with little more burr than edge leading by hand. When I use a fore and aft pass, I'm grinding in both directions, lightly on the edge leading to remove the burr as I go, and a little more pressure on the edge trailing to impart that nice grind pattern I see from my belt sander. While it's impossible to duplicate the effect of speed from the sander, it does seem that using an edge trailing stroke helps impart a less fractured edge. The challenge in this case is in limiting the amount of burr to be cleaned up.
HH
HH
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David, took my time on a 154cm blade using just the coarse side of a no-name combo grit SiC 8" stone. Using, with very light pressure, the above-mentioned fore and aft stroke (which I've been experimenting with recently but haven't really adopted till today), got it as clean as possible and stropped with black emery cake from Sears. There's no visible burr at 12x and the result closely resembles what I can get from a soft Arkansas or slightly better. If I assume it's approx 200 grit, then my outcome appears to be very similar to what I'd expect from a belt sander at that grit. I'm impressed - I was planning on flipping the stone and using the fine grit side of it, but don't want to take any more metal off when I've just produces a surprisingly fine edge. Using my standard "field test" it dry-shaved my cheek stubble with surprisingly little drag - almost no tug at all. I'm on the verge of partially retiring most of my diamond and Arkansas stones. I'll have to use this edge for a few days/weeks and maybe put it back on the fine side using the same technique, see if I can't rival or exceed the best I can get from my other stones.
Best of luck with your retention testing, I can't imagine the fine edge outlasting with sisal as the test material, but without getting to it who could say?
HH
Best of luck with your retention testing, I can't imagine the fine edge outlasting with sisal as the test material, but without getting to it who could say?
HH
David Martin
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Heavy, I didn't get to cut some sisal rope this weekend . Just had other pressing duties .
But I'll try this coming weekend . Now, tell me what your meaning by a 'fore and aft' stroke . Is it both a push then a pull stroke ? So, you think the stone is about 200 grit and after stropping on black emory cloth/cake the scratch pattern left looks to be 600-800 grit and it cuts about like it as well ! Interesting . I've not stropped on that material . Cutting sisal rope is a lot like cutting wiskers . The fine edge does cut nice at first . I could push cut but just go ahead and use the same cutting stroke as normal on all so everything is equal . I fail to see much difference in the two type cutting . As far as efficient use of energy and the movement type throws more of the edge surface into the material being cut . So, you don't get wear just at one area . Also, the D2 steel has 1% V in its mix which is supposed to really help with edge retention . Will that be enough to combat the coarse edge of 440C and enhance its own fine edge ? I don't really know . Thats what will make this interesting . I won't be back home until the weekend . DM
But I'll try this coming weekend . Now, tell me what your meaning by a 'fore and aft' stroke . Is it both a push then a pull stroke ? So, you think the stone is about 200 grit and after stropping on black emory cloth/cake the scratch pattern left looks to be 600-800 grit and it cuts about like it as well ! Interesting . I've not stropped on that material . Cutting sisal rope is a lot like cutting wiskers . The fine edge does cut nice at first . I could push cut but just go ahead and use the same cutting stroke as normal on all so everything is equal . I fail to see much difference in the two type cutting . As far as efficient use of energy and the movement type throws more of the edge surface into the material being cut . So, you don't get wear just at one area . Also, the D2 steel has 1% V in its mix which is supposed to really help with edge retention . Will that be enough to combat the coarse edge of 440C and enhance its own fine edge ? I don't really know . Thats what will make this interesting . I won't be back home until the weekend . DM
Jason B.
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On the DMT XXC, if you buy this stone you will find pressure to be the biggest enemie. You will also find that it really does work best on very hard or very wear resistant steels (as all diamonds do) and softer steels are more or less beat to sh!# by the fixed diamond abrasive of that grit.
On harder steels getting a burr free edge from the XXC is actually very easy if you know how to use proper pressure with diamond stones but if not the edge will look like you dragged it down the sidewalk and feel as sharp.
With the softer steels like AUS8 it really doesn't matter how little pressur you use, the diamonds are just too hard for the steel and end up gouging the metal. In truth its not a stone I'd want to finish a "softer" steel with because its actually damaging and yields poor edge quality.
Being a fixed abrasive of a large grit has shown some issues of its own when speaking of the finished edge. Because the abrasive does not move a missed stroke or slip in angle can cause the apex of the edge to collide directly into the abrasive causing flattening of the edge like ....well......smacking your edge into a hard diamond
Its a very useful stone and works great to flatten water stones (my main use) but is also a great metal remover and a near replacement for a belt sander.
Understanding how different metals and abrasive interact with each other is probably the most difficult aspect to grasp. I've been trying to figure it out myself for a few years now and have a decent idea but with all the steel and stone types its a deep rabbit hole.
Somewhat off topic but, don't you find using a coarse stone all the time that your removing excess metal making blade life shorter? For me its one of the aspects of using a fine finishing stone, I'm only removing metal that needs to be removed preserving the bevel geometry and extending blade life.
What's your take on it?
On harder steels getting a burr free edge from the XXC is actually very easy if you know how to use proper pressure with diamond stones but if not the edge will look like you dragged it down the sidewalk and feel as sharp.
With the softer steels like AUS8 it really doesn't matter how little pressur you use, the diamonds are just too hard for the steel and end up gouging the metal. In truth its not a stone I'd want to finish a "softer" steel with because its actually damaging and yields poor edge quality.
Being a fixed abrasive of a large grit has shown some issues of its own when speaking of the finished edge. Because the abrasive does not move a missed stroke or slip in angle can cause the apex of the edge to collide directly into the abrasive causing flattening of the edge like ....well......smacking your edge into a hard diamond
Its a very useful stone and works great to flatten water stones (my main use) but is also a great metal remover and a near replacement for a belt sander.
Understanding how different metals and abrasive interact with each other is probably the most difficult aspect to grasp. I've been trying to figure it out myself for a few years now and have a decent idea but with all the steel and stone types its a deep rabbit hole.
Somewhat off topic but, don't you find using a coarse stone all the time that your removing excess metal making blade life shorter? For me its one of the aspects of using a fine finishing stone, I'm only removing metal that needs to be removed preserving the bevel geometry and extending blade life.
What's your take on it?
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That's it, by varying the amount of pressure one way or the other it appears you can get different grinding characteristics. It's also helped a lot with my stropping technique.
Yeah, I'm kind of at a loss. I figured I'd get some change, didn't expect it to be quite so dramatic. My usual edge with this grit is barely capable of knocking a few arm hairs off. On the other hand, it probably doesn't perform like a coarse edge aught to at this grit either. Edge retention will have to be determined later, as well as the ability to refresh the edge with the black emery strop.
I'm curious, I was also thinking what other materials might make for good testing. Ty raps come to mind, drawing cut with the coarse edge and a strict push cut for the fine edge. They're no the cheapest test stock, but very tough and the test duration should be considerably shorter. If a heavy fish scale could be included somehow into the mix it would get even more interesting.
HH
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I'm starting to believe that blade life and different grinds is largely an individual user aspect. When using a fine edge on my hard-use knives and using a primary/secondary bevel I found myself having to reestablish the secondary bevel so frequently that it was removing a lot of metal to keep it in good shape. With a fine edge and a single bevel one still has to drop down a few grit levels from time to time and that eats steel as well. With a hard used coarse edge I'm only using a single bevel and can refresh it with just a few passes even if it's pretty beat up. It's difficult to say for sure which removes more metal in the long run. The casual user will likely get more life from a fine edge, but a coarse edge done well and used casually can go for many long months with zero attention. I am slowly coming to the conclusion that the easiest edge for most people to achieve and maintain is somewhere in between the two. Getting a high quality coarse or fine edge requires a little more understanding of all the variables with respect to steel and grinding media. It is very much like jumping down the rabbit hole. For each steel type and application there's going to be a perfect grinding media and edge angle etc.