How to sharpen blades greater than 59HRC
- This topic has 10 replies, 6 voices, and was last updated 08/19/2021 at 3:08 am by
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Welcome to the Wicked Edge forum, Bryce Herbst.
I’m a proponent of using the sharpening medium that will sharpen your knife’s steel the best. Your fears of damaging those steels are well founded and based in real experiences. Harder steels such as you related, harder than HRc 59-60 can be more on the brittle side and may suffer damage in the form of edge chipping or fall off. Whereas the softer steels may fold or roll the edge with damage from use.
I almost exclusively use whetstones made to be used with the Wicked Edge systems for these harder steels. Still, the rule’s not so black and white. Some of the harder steels I’ve found do sharpen quite well and easily with diamond sharpening stones. Whereas other similarly rated hard, but different steels will suffer severe edge damage with diamond stones.
I have not experienced any edge damage or edge failure sharpening my harder steel knives with whetstones. The problem I found trying to sharpen these hard steels with the diamond stones is sometimes the edge failure doesn’t occur till the end of my sharpening progression when I’m using the finer grits. Then not only did I waste my time and effort but I also wasted edge steel. Then I have to start all over again while wasting more steel as I remove the damage from using the diamond stones, first. With other hard steels I’ve had edge damage right from the get-go with the diamond stones. I had the same poor results when I tried to use only the finer diamond stones, too.
There is no set progression I would recommend for you to follow when sharpening knives. I prefer to always start at the highest or finest grit I can use effectively. If it’s not doing it, then I work backwards to a lower coarser grit till you find the grit appropriate for the duty. For instance, if you start at 1000 grit and it’s requiring too much time and effort to remove or reshape the damaged steel, then move down to 800 grit. If that’s not coarse enough go down another coarser step. The goal is to use the finest grit you can use to repair and reshape the steel effectively. Any coarse scratches we apply while sharpening a knife edge will have to be smoothed over and polished back out during the sharpening process with subsequent finer grits. The best way to save yourself work is to use the finest grit you can use well. Experience is the best way to learn these lessons of which grit and which mediums are best to use.
I don’t find the W.E. ceramic stones to be a substitute for ceramic whetstones on these harder steels. Although, some W.E. users enjoy the ceramics stones for the enhanced sharpness and edge polish they can produce when these stones are used well and appropriately.
BTW: The Twin Cermax knives I believe are HRc 66. It’s 67 if it’s the Damascus model.
Marc
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It seems to me that the harder that a steel is the better that diamond stones would work. I question the actual hardness of those types of knives. I don’t believe that they are as hard as claimed. I have some knives that measure between 50 – 55RC according to my Tsubosan files and my diamond stones rip the steel off like it’s nothing. Maybe the Japanese steel is softer than claimed and that is why diamonds tear it up so bad?
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That could be a reason if they are using too much pressure with the diamond stones. Diamond stones don’t need a lot of pressure. I use only enough pressure to keep the stones flat and even against the edge of the blade. It does take practice though. I used to catch myself applying too much pressure occasionally.
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Harder steels such as you related, harder than HRc 59-60 can be more on the brittle side and may suffer damage in the form of edge chipping or fall off. Whereas the softer steels may fold or roll the edge with damage from use. I almost exclusively use whetstones made to be used with the Wicked Edge systems for these harder steels. Still, the rule’s not so black and white. Some of the harder steels I’ve found do sharpen quite well and easily with diamond sharpening stones. Whereas other similarly rated hard, but different steels will suffer severe edge damage with diamond stones. I have not experienced any edge damage or edge failure sharpening my harder steel knives with whetstones. The problem I found trying to sharpen these hard steels with the diamond stones is sometimes the edge failure doesn’t occur till the end of my sharpening progression when I’m using the finer grits.
You have succinctly described my problems sharpening an M390 knife. I suspect most of my problems arose from carbide tear out, perhaps the result of the machining method diamond stones use. Diamond stones are anchored in a hard matrix and they have to cut hard carbides also anchored in the hard matrix of the knife steel. As hard steels also may become more brittle (as a result of the carbide formation that makes them hard) this stresses the blade matrix until it exceeds its yield strength and hard carbides are torn out – leaving what seems to be chips in the very edge of the edge apex. My own observations suggest this is the problem I had. I solved it (quite spectacularly I might add) by going to Chosera stones in WE paddles which completely solved this problem – and took me to a satisfactory impressive mirror edge.
Whetstones (water stones) use – to at least some extent in my opinion – a different machining process. As I think of the slurry formed, some (much?) of the abrasive is no longer held in the matrix of the stone but becomes part of a free abrasive machining process (similar to a wire saw used in silicon chip manufacture) and is as much or more of a lapping process as it is a cutting process. The abrasive grains tumble across the surface of the edge bevel and instead of lateral forces that tear out the carbides they drive the carbides into the matrix – smoothing the surface out and refining it in a good way. It made a believer out of me and my set of Choseras are definitely now part of my toolkit – to use when I want this kind of edge with surprisingly little time and effort.
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Hey Bryce, sounds like you’re kind of new to sharpening. I would strongly suggest you break in your stones by going through at least ten junk knives before getting into your wife’s assortment. And don’t stop there, spend a lot of time honing your own skills before getting into the expensive ones because any damage is pretty much irreversible forcing you to remove product to cover up your mistakes. Just my two cents.
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Thanks for the good thoughts and advice, Richard.
I bought three sets of Naniwa Chosera WE paddles and am now learning how to use and care for them. So far, so good.
I’ve sharpened about a dozen knives for my neighbors. All came out razor sharp and they loved the results. However, none was in the 61+ HRC range. I bit the bullet and worked on our Shun Premier and MAC MTH-80; being very careful to use downward-outward strokes. They came out beautifully
Next week I’m going to work on one of our SG2s. You guys have been a great help in learning about this whole new world.
Your guidance, help and support are great and greatly appreciated.
I just happened to sharpen my Delica 4 in ZDP-189. I checked the log and I noticed a note that said “No grits lower than 600.” I had a deep chip near the tip and it was going to take hours to erase it with 600, so I bit the bullet and went to my very-well broken-in 400s. Sure enough, when I checked with my ‘scope, now there were three chips, each at least as deep as the first one. This all happened with edge-leading strokes.
I have a ceramic knife I bought just to experiment with the diamond stones and I learned the same lesson there. Nothing lower than 1000 grit.
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