+- The BESS Exchange is sponsored by Edge On Up (http://bessex.com/forum)
+-- Forum: BESS Forums (http://bessex.com/forum/forumdisplay.php?fid=1)
+--- Forum: All About Edges (http://bessex.com/forum/forumdisplay.php?fid=21)
+--- Thread: Sharpening High Hardness Edges in Carbon Steels (/showthread.php?tid=264)
Sharpening High Hardness Edges in Carbon Steels - me2 - 01-26-2018
Inspired by Mark's comments in the other thread, I decided to start my first thread here. The following is based on sharpening my 2 Japanese kitchen knives and a knife I made from M2 high speed steel with a hardness of 64.5 to 66 HRc. In other words, it's based on fairly limited experience.
First, I really like the quiet complexity of Wa handled Japanese kitchen knives. It's subtle, and often unrealized until you try to thin an edge or really look closely at the geometry in preparation to sharpen. These two knives are described below.
Tojiro ITK 120mm Kurouchi Petty - this was my first Japanese Kitchen Knife (JKK). It has a blade of the prescribed length, with a fairly simple handle of Ho wood and a plastic ferrule. The blade is the reason for the quiet complexity comment above. It tapers from tang to tip, from spine to grind line, from grind line to edge bevel, and from edge bevel to apex. It is laminated with a core steel of Hitachi White #2, with an estimated hardness of 60 to 61 HRc, estimated by the distributor.
Misuzu 165mm Bunka - This was my second, and is currently my most used kitchen knife. It is less complex, in some ways, but more in others. It doesn't taper from the spine to the grind line, but has a fairly wide blade grind to a very thin edge. It's complexity lies in the stainless laminated outer layers over a core of carbon steel I'm not familiar with, but appears similar to O1 or O2, or so I'm told. The estimated hardness is also 60 to 61.
Both of these knives had edge bevels between 0.003 and 0.006 inches thick, which is extremely thin by most standards. Upon receiving them I rebeveled them to 12 degrees per side on my sharpening block guide using a 220 Norton water stone. Given the thickness, this went pretty quickly. I've found edge geometry to be way more of an influence on sharpening time than steel type, but you have to have either very good testing procedures for sharpening time or huge differences in geometry to really be able to tell for sure.
These generally don't see heavy use. The petty has seen use as a utility knife for various things, but the Bunka has been a dedicated kitchen knife for everything from onions to spaghetti squash. I say that to say they're generally not too dull when I sharpen them.
The first thing I do is cut VERY lightly into a medium grit 1000 grit king stone. Then I do 20 passes per side until I get a burr, which generally only requires one set of passes on each side. For finishing, I generally use a Spyderco Sharpmaker, with the 15 degree setting, and stop at the Medium stone flat surfaces. (I rarely use the corners for anything anyway). This will generally give an edge that will whittle my head hair and cut arm hair above the skin with and against the grain. Sometimes I finish with a 4000 grit water stone, but that takes more care and time, though I think it potentially gives a sharper edge, limited by how much patience I have at the time.
The third blade mentioned was a Puuko style utility knife with a 10 degree per side bevel ground on with my small belt sander. The steel was recycled from an industrial hacksaw blade, one of the few I've found that aren't bi-metal. It was one piece of M2 high speed steel with what I can only describe as excellent heat treatment, with an exceptionally high hardness of 64.5 to 66. The blade was 1mm thick and 5" long, with a cord wrapped handle. It has been recycled into a different blade now, which isn't finished. It was generally sharpened the same as the others above, keeping the bevel to a manageable size by grinding when needed. I don't recall using the 4000 grit stone on it though. In spite of it's high hardness, it survived brief use as a throwing knife.
These three knives did not take kindly to large burrs. The M2 knife didn't form foil like burrs even on my belt sander, but I also took care to avoid those as well. The burrs on all three are quite strong, unless over done, and wouldn't come off with stropping. They generally just scrape up the surface of the leather and remove the compound. They have to be abraded off with a stone, hence the angle change from 12 to 15 degrees. Burrs on the M2 knife could be power stropped off with a leather belt on a belt sander with white buffing compound. I've not tried this on the JKKs.
Edge holding on the M2 blade was simply the best I've tried; able to hold an edge that would tree top arm hair after cutting 10 yards of cardboard.
The high hardness keeps burrs to a minimum on all 3 knives. Burrs are also the opposite of ductile and come off on the stones with relative ease, 5 to 10 passes per side on the Sharpmaker Medium rods. The extremely thin edges sharpen quickly and don't require power equipment to sharpen in less than 5 minutes.
My battery is dying. More tomorrow.
RE: Sharpening High Hardness Edges in Carbon Steels - grepper - 01-26-2018
Great post Mr. Me2. Thanks for posting it. Very interesting.
My experience sharpening very hard steel blades is from only a couple that I did years ago using the Tormek. So, very limited. I have no idea how hard the steel was except that it was much harder than anything else I had sharpened. They took forever to sharpen, and it was very difficult to affect that edge at all. I had to use a lot of pressure just to grind the edge.
What I remember was that not only was it difficult to form a burr at all, but what little burr formed was very small. Kind of like the M2 you describe except the burr was very brittle and broke off easily. That’s quite different from the tough burrs you describe. That observation has no meaning whatsoever other than whatever steel was in those blades I sharpened while very hard, was probably much more brittle than your blades. I suspect your blades would have better edge retention, chip less easily, and are probably better steel.
Got to hand it to you for being able to sharpen that super hard M2 in 5 minutes! My experience was not that easy. It could very well have something to do with the skill, of lack thereof, of the person doing the sharpening.
“Edge holding on the M2 blade was simply the best I've tried; able to hold an edge that would tree top arm hair after cutting 10 yards of cardboard.”
Wow! That’s impressive. Makes me wonder if shelling out the $$$ for a super steel knife might be worth it, if for nothing else than something to compare to the run of the mill cutlery I’m used to. Onion other hand, I like it when my knives dull so that I have something to sharpen.
Did you take any sharpness readings on those knives before/after sharpening?
RE: Sharpening High Hardness Edges in Carbon Steels - me2 - 01-26-2018
I must've been unclear. The thin edges of the JKKs are the ones that sharpen so quickly. Puuko style grinds are time consuming to sharpen even when not made from high wear steels. I have taken readings on the petty. It's my record holder at about 75, estimated in conversation here with EOU.
I had a session with the petty sharpening with no burr, and it was probably sharper after that, but l didn't measure it.
RE: Sharpening High Hardness Edges in Carbon Steels - grepper - 01-26-2018
I had to look up Puukko.
What is a Puukko style blade? Wiki sez, " a single curved cutting edge and, usually, a flat back." Does that mean a chisel (single bevel edge?). What makes them more time consuming to sharpen?
RE: Sharpening High Hardness Edges in Carbon Steels - me2 - 01-26-2018
They are a traditional knife of Scandinavia, Finland, and nearby areas. They typically have fairly thin blades, 3/32" - 1/8" thick and 3 to 4 inches long. The difficulty lies in they typically have no primary grind. Just a 10 to 12 degree per side edge bevel that's 1/4 - 3/8 inch wide. When sharpened, that wide bevel is layed flat on the stone and the whole thing planed down. Easy to hold the angle, but a lot of metal to remove.
RE: Sharpening High Hardness Edges in Carbon Steels - me2 - 01-26-2018
Helle and Mora are two examples of brands.