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- Apr 10, 2000
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Hi All,
The following is the result of partly unsuccessful test of superhard vs. more widespread, softer edge. Main failure was the problem with the microscope and the knife blades, I couldn't get good shots of the deformations, the table on the microscope is horizontal and to get the best angle I had to hold the knives at the angle, which wasn't steady enough with my hands and I had no device to do that. Plus, due to processing error I've lost some of the images. Anyway...
Test knives: Benchmade 710 m2 steel, rehardened by Phil Wilson, reground by Tom Krein, 64HRC and Calphalon paring knife, presumably 440A class steel, 54-56HRC.
The popular opinion is that 64HRC or even 60HRC edges are excessively prone to chipping and very hard to sharpen, while softer edges are easier to sharpen, don't chip and therefore are more useful. At least in my experience, hard edges are not all that chippy and the test was mainly to estimate to some degree the damage taken by both types of edges.
The edge on BM 710 is ~13-14deg per side, measured using 2 different methods, height from the sharpening stone, and by measuring bevel width and edge thickness behind the edge. Calphalon was never used until that day and I've sharpened it using Edge-Pro to 15 deg. per side edge. Final finishing grit was 0.25mic diamond loaded strop followed by stropping on the plain leather strop. Calphalon having slightly thicker edge had a minimal advantage.
Test cuts were done on the aluminum(?) bottle caps. I've used about 25-30mm long sections of the edge on both knives to slice through the metal.
I've already done metal cutting tests with 710, and it never sustained any significant damage, that included copper, aluminum, tv cable, which has steel in it too, so the interesting part was what'd happen to calphalon parer.
First, I cut the tops of 8 caps from the bottles using 710, and then proceeded cutting those flat discs in half with the calphalon knife. Considering that BM710 blade was in contact with the glass during all that time and Calphalon was not, the test was easier for Calphalon knife.
After cutting 5 discs Calphalon was so dull I gave up on further testing. Details below.
Aluminum or any other soft metal isn't your typical cutting material, but to observe the same effect(s) on soft materials I'd have to cut very long time
Besides, part of the test was that chippy vs. tough theory.
The Images:
Benchmade 710 before and after ~120x magnification:
As you can see very little damage to the edge. Despite cutting much more metal. No chipping either.
Calphalon "before" photo was lost, but it was a mirror polished pristine edge. Post testing - larger section 65X, 2 damaged sections at 120x and 150x.
As you can see, calphalon edge is completely dull, the edge is no more, it's rounded. Interestingly, it didn't loose significant chunks of metal, I was sortta expecting that, but considering that the test was very short, that's probably no surprise. Neither knife sustained irreparable edge damage, in fact BM710 sustained pretty much none.
Ease of sharpening - Obviously, calphalon is a winner there, using edge pro, I started out with 120 grit stone, and it took about 2 minutes per side to thin down initial ~40 deg inclusive angle to 30 with 120 grit stone and I did feel it was an overkill for that knife.
Restoring the edges - After cutting 8 discs BM710 it did loose shaving ability, restoring it needed about 10 strokes per side on 0.25mic diamond charged strop. I didn't have to strop or steel during all 8 cuts.
Initially, I was more focused on the edge damage, but later, after testing Calphalon, I realized, edge restoration was considerable problem, so I went back to BM710, cut 3 remaining discs in half, the edge did degrade very slightly, however restoring it required 5 strokes on the same 0.25mic strop.
After cutting 2 discs in half, i.e. 4 cuts, Calphalon not only lost shaving ability, but I could feel I had to make more effort to cut through the metal. I stopped, examined the blade, in few places it the edge was quite rippled already. I've used smooth steel, and to my surprise, about 10 strokes per side brought back shaving sharpness, mostly Few places that were damaged bad enough were not that easy to restore.
I made 2 more cuts, that's disc #3 and Calphalon lost sharpness again. steeling(25 strokes per side) did bring back some of it, but this time more of the affected edge remained dull. After disc #4 it became increasingly difficult to cut. disc #5 was considerably more difficult. I couldn't make cuts all the way through along the diameter. I've tried restoring the edge with a smooth steel, fail, then ceramic stick, which didn't help much either. At that point I gave up. It was clear I needed to spend either hour or two with that fine ceramic stick, or grab much more coarse stone.
Results summary: Well, as it was expected I didn't get any chipping on 64HRC M2 steel. It was also very quick process to restore the edge, nothing more than 0.25 mic diamond charged strop.
Calphalon on the other hand was also very easy to restore the edge initially, given that it needed just the smooth steel, but that still left flattened sections, but main problem was that secondary dulling, and subsequent dulling-s were happening at faster rate and I was unable to restore the edge neither with smooth steel, nor with much coarser(compared to 0.25mic) ceramic stick.
My interpretation of the test results:
1) In the end, properly heat treated, even at 64HRC knife isn't that easy to chip, at least for most of the knife tasks. I have experience with M2, CPM 10V, CPM 125V, M4, ZDP-189, all at 64HRC and above.
This particular blade was in contact with glass, cut metal, earlier it cut harder metals as well, and no chips. I have no illusions that given enough force and hard enough medium I can chip it, but for majority of knife works it works just fine. Soft steel on calphalon didn't last nearly as long, and while first edge restoration was quick, the rest of the process was much longer or not possible with smooth steel or fine grits.
2) As it is, the calphaon edge today, it's useless. To restore it I have to go back to coarse stone, and remove considerable amount of metal. Which, besides the edge durability, raises the problem of the knife durability itself. I'm not so sure how many sharpening like that a knife will survive.
3) Harder steel cut much longer w/o taking any significant damage. Well, no big discovery there, although no chipping can be a surprise to some
4) Ease of sharpening, to me it's overrated. Given the proper sharpening tools, calphalon is super easy, and most of the other steels I mentioned are moderate. Although, highly wear resistant steels can be pain, but hardness doesn't play the only critical role there, it's steel composition too, which is easily demonstrated by Aritsugu A-Type gyuto, its gokinko steel, at only 60HRC it is considerably harder to sharpen than 63-65HRC Aogami and Shirogami knives.
In the end, it's more about personal preferences, this isn't a rant against soft blades, but I still think hard blades receive quite a bit undeserved negative rap, or at least a lot of fears about them being too brittle are unfounded.
Next time I'll experiment with wood whittling, which most likely will induce a lot more lateral loads on the knives, and I suspect Calphalon will fare even worse. Although, micrographs remain a problem, I need some sort of contraption to hold the blade a an arbitrary angle in 3 dimensions, not sure what though.
The following is the result of partly unsuccessful test of superhard vs. more widespread, softer edge. Main failure was the problem with the microscope and the knife blades, I couldn't get good shots of the deformations, the table on the microscope is horizontal and to get the best angle I had to hold the knives at the angle, which wasn't steady enough with my hands and I had no device to do that. Plus, due to processing error I've lost some of the images. Anyway...
Test knives: Benchmade 710 m2 steel, rehardened by Phil Wilson, reground by Tom Krein, 64HRC and Calphalon paring knife, presumably 440A class steel, 54-56HRC.
The popular opinion is that 64HRC or even 60HRC edges are excessively prone to chipping and very hard to sharpen, while softer edges are easier to sharpen, don't chip and therefore are more useful. At least in my experience, hard edges are not all that chippy and the test was mainly to estimate to some degree the damage taken by both types of edges.
The edge on BM 710 is ~13-14deg per side, measured using 2 different methods, height from the sharpening stone, and by measuring bevel width and edge thickness behind the edge. Calphalon was never used until that day and I've sharpened it using Edge-Pro to 15 deg. per side edge. Final finishing grit was 0.25mic diamond loaded strop followed by stropping on the plain leather strop. Calphalon having slightly thicker edge had a minimal advantage.
Test cuts were done on the aluminum(?) bottle caps. I've used about 25-30mm long sections of the edge on both knives to slice through the metal.
I've already done metal cutting tests with 710, and it never sustained any significant damage, that included copper, aluminum, tv cable, which has steel in it too, so the interesting part was what'd happen to calphalon parer.
First, I cut the tops of 8 caps from the bottles using 710, and then proceeded cutting those flat discs in half with the calphalon knife. Considering that BM710 blade was in contact with the glass during all that time and Calphalon was not, the test was easier for Calphalon knife.
After cutting 5 discs Calphalon was so dull I gave up on further testing. Details below.
Aluminum or any other soft metal isn't your typical cutting material, but to observe the same effect(s) on soft materials I'd have to cut very long time
Besides, part of the test was that chippy vs. tough theory.The Images:
Benchmade 710 before and after ~120x magnification:
As you can see very little damage to the edge. Despite cutting much more metal. No chipping either.
Calphalon "before" photo was lost, but it was a mirror polished pristine edge. Post testing - larger section 65X, 2 damaged sections at 120x and 150x.
As you can see, calphalon edge is completely dull, the edge is no more, it's rounded. Interestingly, it didn't loose significant chunks of metal, I was sortta expecting that, but considering that the test was very short, that's probably no surprise. Neither knife sustained irreparable edge damage, in fact BM710 sustained pretty much none.
Ease of sharpening - Obviously, calphalon is a winner there, using edge pro, I started out with 120 grit stone, and it took about 2 minutes per side to thin down initial ~40 deg inclusive angle to 30 with 120 grit stone and I did feel it was an overkill for that knife.
Restoring the edges - After cutting 8 discs BM710 it did loose shaving ability, restoring it needed about 10 strokes per side on 0.25mic diamond charged strop. I didn't have to strop or steel during all 8 cuts.
Initially, I was more focused on the edge damage, but later, after testing Calphalon, I realized, edge restoration was considerable problem, so I went back to BM710, cut 3 remaining discs in half, the edge did degrade very slightly, however restoring it required 5 strokes on the same 0.25mic strop.
After cutting 2 discs in half, i.e. 4 cuts, Calphalon not only lost shaving ability, but I could feel I had to make more effort to cut through the metal. I stopped, examined the blade, in few places it the edge was quite rippled already. I've used smooth steel, and to my surprise, about 10 strokes per side brought back shaving sharpness, mostly
Few places that were damaged bad enough were not that easy to restore.I made 2 more cuts, that's disc #3 and Calphalon lost sharpness again. steeling(25 strokes per side) did bring back some of it, but this time more of the affected edge remained dull. After disc #4 it became increasingly difficult to cut. disc #5 was considerably more difficult. I couldn't make cuts all the way through along the diameter. I've tried restoring the edge with a smooth steel, fail, then ceramic stick, which didn't help much either. At that point I gave up. It was clear I needed to spend either hour or two with that fine ceramic stick, or grab much more coarse stone.
Results summary: Well, as it was expected I didn't get any chipping on 64HRC M2 steel. It was also very quick process to restore the edge, nothing more than 0.25 mic diamond charged strop.
Calphalon on the other hand was also very easy to restore the edge initially, given that it needed just the smooth steel, but that still left flattened sections, but main problem was that secondary dulling, and subsequent dulling-s were happening at faster rate and I was unable to restore the edge neither with smooth steel, nor with much coarser(compared to 0.25mic) ceramic stick.
My interpretation of the test results:
1) In the end, properly heat treated, even at 64HRC knife isn't that easy to chip, at least for most of the knife tasks. I have experience with M2, CPM 10V, CPM 125V, M4, ZDP-189, all at 64HRC and above.
This particular blade was in contact with glass, cut metal, earlier it cut harder metals as well, and no chips. I have no illusions that given enough force and hard enough medium I can chip it, but for majority of knife works it works just fine. Soft steel on calphalon didn't last nearly as long, and while first edge restoration was quick, the rest of the process was much longer or not possible with smooth steel or fine grits.
2) As it is, the calphaon edge today, it's useless. To restore it I have to go back to coarse stone, and remove considerable amount of metal. Which, besides the edge durability, raises the problem of the knife durability itself. I'm not so sure how many sharpening like that a knife will survive.
3) Harder steel cut much longer w/o taking any significant damage. Well, no big discovery there, although no chipping can be a surprise to some
4) Ease of sharpening, to me it's overrated. Given the proper sharpening tools, calphalon is super easy, and most of the other steels I mentioned are moderate. Although, highly wear resistant steels can be pain, but hardness doesn't play the only critical role there, it's steel composition too, which is easily demonstrated by Aritsugu A-Type gyuto, its gokinko steel, at only 60HRC it is considerably harder to sharpen than 63-65HRC Aogami and Shirogami knives.
In the end, it's more about personal preferences, this isn't a rant against soft blades, but I still think hard blades receive quite a bit undeserved negative rap, or at least a lot of fears about them being too brittle are unfounded.
Next time I'll experiment with wood whittling, which most likely will induce a lot more lateral loads on the knives, and I suspect Calphalon will fare even worse. Although, micrographs remain a problem, I need some sort of contraption to hold the blade a an arbitrary angle in 3 dimensions, not sure what though.
