- Joined
- Jan 14, 2016
- Messages
- 126
I'm posting this because I've been asked both by members here and on Reddit to talk about some problems we all run into when we need to sharpen difficult steels, how to choose an appropriate edge angle, to micro-bevel or not to micro-bevel and generally set yourself up for success at the sharpening bench.
I've had good results with a Wicked Edge system. The reason i chose it is that it securely clamps the knife in place in a repeatable way and it has very fine, precise angle adjustments independently on both sides. There are plenty of other systems on the market on which similar results can be achieved. Edge Pros, KMEs, Vipers, Tormeks and others. Dealing with these steels really demands ceramic and the very least and better yet, mono-crystaline diamond abrasives.
The danger here is that aggressive abrasives at lower grit counts can grab large carbides out of the blade edge and tear them out of the blade, leaving a chip or a gash in the edge. for each method of sharpening, the fix for this is always the same, very light pressure, lots of strokes and lots of patience. There really isn't a way around that when dealing with these harder steels. One has to be willing to spend significantly more time laboriously working with the same grade stones, removing all of the previous grade's scratch marks before moving onto the next. To put this in perspective. These edges which I put on these Maxamet knives took a little over two hours a piece under the wicked edge. The trade off is that I won't have to do this again for quite a while.
Setting up for success on the sharpening bench is largely a matter of prep work. This means protecting the knife. I usually wrap up the handles and actions in saran wrap and use electrical tape to seal the action off from the blade. I do this because I don't want steel or diamond particles finding their way into the action. I'll also keep a wet soapy sponge or paper towel on hand to clean up metal shavings after each grit, this becomes especially important when polishing. One piece of 600 grit dust leftover on the blade when you're in the final 3 micron film stage can cause a gouge in the edge bevel and if that happens, i'll have to go back to the beginning of the polishing stages and work that gouge out and finish again. So cleanliness pays big dividends here. Also, check your settings and your angles often. On a Wicked Edge, this means checking the thumb screws for tightness every few minutes. They don't usually, but can loosen up in use. You don't want to be rounding off what should be a flat bevel because your hardware is loose. So when I'm all set up and ready to sharpen, my knife will look something like this.
Next Topic: How to choose an edge angle.
Most of the time, this will already be done for us by the manufacturer. In cases of quality knives, these blades have a warranty and a repair department which will have to fix the knife should anything happen. So these companies put some thought into their edge geometry and apply the sharpening angle which will make these kinds of returns as unlikely as possible. This is why you see Benchmade Bugouts with factory edges somewhere around the 18 degree mark and Benchmade Contigos in CPM-M4 around the 15.5 degree mark.
So how do we make this call when we want to change the angle or we want better retention than the factory (Or custom maker) gave us? Without getting too deep into the weeds on this, a good general rule is that we should take into account four things when choosing an edge angle. The properties of the steel in question, the thickness behind the edge, how the edge will be used, and whether or not there will be a micro-bevel.
For softer steels, putting a micro-bevel on the edge will not generally help the retention because the purpose of a micro bevel is to improve the toughness of an edge. If the steel is soft (below about 58 HRC is what I would consider soft) its likely quite tough, so the micro-bevel will not have any real purpose.
For harder steels with good toughness, (S30V, 154CM, S35VN, LC200N, etc.) I would only apply a micro-bevel if it were getting a lower angle on the edge 16 degrees per side or less. Because these steels are already pretty tough, a higher angle plain edge won't benefit from a micro-bevel, but a lower angle edge will wear down very quickly due to there not being enough metal behind it to retain its stability.
Now why would I choose to put a lower angle edge on a tough, but not particularly hard edge like that? Its the thickness behind the edge that makes that decision for me. If I have an S30V knife which is 0.050" right behind the bevels. I'm going to need to put a relatively narrow angle on that to make it any kind of decent slicer, but if I do that, it will dull down very quickly because there won't be much width right behind the apex of the cutting edge, so I will need micro-bevel to make this edge last. But who says it needs to be a great slicer? What if this is going to be a well abused camp knife? In that case, I'm going to go up to 24 degrees per side, leave it at 600 grit finish, and call it good because what I want is toughness and edge stability above all else.
What if this same knife was only .015" behind the cutting edge and I knew it wasn't going to get any hard use? In this case, I think the best move would be to set the bevels at 18 or 19 degrees per side because I don't need to worry too much about toughness or stability, the steel is already pretty tough and strong. What I need to worry about here is simple slicing longevity, and that means I want to polish my edge because that does have a big impact on edge retention once hardness is above about 58-59 HRC. I could choose to add a micro-bevel, and it might make the edge last a slight bit longer, but it might not either.
So you begin to see how I apply these four considerations when choosing an angle, finish and micro-bevel. What about these super hard steels though? With these steels, my main concern is toughness. The very thing they lack. I don't want to give a blade back to a customer without taking every step I reasonably can to make sure that it won't chip or crack on the edge. Because toughness is my main concern and the purpose of a micro-bevel is to improve edge toughness, I will always apply one to very hard and brittle steels like Maxamet or REX121. Because I already know I will be using a micro-bevel, I'll go down as far as 12 or 13 degrees per side on the edge bevels as log as its thick enough behind the edge of the knife. (.020" or more)
This brings me to another point about micro-bevels. Whatever you polish your main edge bevels to is also what you should polish your micro-bevels to. If I have an abused camp knife made out of a harder steel (why a maker would do this is another matter) I would leave it at 600 grit because It needs to be toothy to rip through things. Then I would also leave my micro-bevels at 600 grit because i want the apex of the micro bevel to be the same width as it would be without. Not so critical for a camp knife like this, but very critical in the manix 2 in maxamet above. if I were to polish the edge bevels up to 3 microns (I don't really see much point in going beyond that, diminishing returns and all) then that is going to give me an apex which is only about 0.15-0.1 microns wide, this is where an edge will cut a free hanging hair under the hair's own weight. If I want that level of sharpness, but I leave the micro-bevel at 1000 grit diamond stone finish, then the actual apex will be much wider than that and will not cut these hairs. If I want that ability, then I need to take the micro-bevel all the way up to where I finished the edge bevels. For this reason, whenever I put a hanging hair edge on a knife like those above, I will also finish the micro-bevels up to that hanging hair sharpness.
This brings me to my last comment about steels in a generality. Steels like Bohler-Uddeholm M390 and its twins (Carpenter CTS-204P and CPM-20CV), S110V, Sleipnr, and a handful of others are excellent "Jack of All Trade" steels. One can put just about any edge of any description on these steels and they will be good to go. You can have a thin cross section behind the edge of a CTS-204P like on this Spyderco Military sprint run, and you can put a very wide angle or a very narrow one, and it will just smile and hold that edge nicely. You can also have a thick-behind-the-edge blade of Sleipnr, like on my Lionsteel SR11B, put a very narrow 12 degree per side edge bevels and it will take it and hold it like a champ.
I've had good results with a Wicked Edge system. The reason i chose it is that it securely clamps the knife in place in a repeatable way and it has very fine, precise angle adjustments independently on both sides. There are plenty of other systems on the market on which similar results can be achieved. Edge Pros, KMEs, Vipers, Tormeks and others. Dealing with these steels really demands ceramic and the very least and better yet, mono-crystaline diamond abrasives.
The danger here is that aggressive abrasives at lower grit counts can grab large carbides out of the blade edge and tear them out of the blade, leaving a chip or a gash in the edge. for each method of sharpening, the fix for this is always the same, very light pressure, lots of strokes and lots of patience. There really isn't a way around that when dealing with these harder steels. One has to be willing to spend significantly more time laboriously working with the same grade stones, removing all of the previous grade's scratch marks before moving onto the next. To put this in perspective. These edges which I put on these Maxamet knives took a little over two hours a piece under the wicked edge. The trade off is that I won't have to do this again for quite a while.
Setting up for success on the sharpening bench is largely a matter of prep work. This means protecting the knife. I usually wrap up the handles and actions in saran wrap and use electrical tape to seal the action off from the blade. I do this because I don't want steel or diamond particles finding their way into the action. I'll also keep a wet soapy sponge or paper towel on hand to clean up metal shavings after each grit, this becomes especially important when polishing. One piece of 600 grit dust leftover on the blade when you're in the final 3 micron film stage can cause a gouge in the edge bevel and if that happens, i'll have to go back to the beginning of the polishing stages and work that gouge out and finish again. So cleanliness pays big dividends here. Also, check your settings and your angles often. On a Wicked Edge, this means checking the thumb screws for tightness every few minutes. They don't usually, but can loosen up in use. You don't want to be rounding off what should be a flat bevel because your hardware is loose. So when I'm all set up and ready to sharpen, my knife will look something like this.
Next Topic: How to choose an edge angle.
Most of the time, this will already be done for us by the manufacturer. In cases of quality knives, these blades have a warranty and a repair department which will have to fix the knife should anything happen. So these companies put some thought into their edge geometry and apply the sharpening angle which will make these kinds of returns as unlikely as possible. This is why you see Benchmade Bugouts with factory edges somewhere around the 18 degree mark and Benchmade Contigos in CPM-M4 around the 15.5 degree mark.
So how do we make this call when we want to change the angle or we want better retention than the factory (Or custom maker) gave us? Without getting too deep into the weeds on this, a good general rule is that we should take into account four things when choosing an edge angle. The properties of the steel in question, the thickness behind the edge, how the edge will be used, and whether or not there will be a micro-bevel.
For softer steels, putting a micro-bevel on the edge will not generally help the retention because the purpose of a micro bevel is to improve the toughness of an edge. If the steel is soft (below about 58 HRC is what I would consider soft) its likely quite tough, so the micro-bevel will not have any real purpose.
For harder steels with good toughness, (S30V, 154CM, S35VN, LC200N, etc.) I would only apply a micro-bevel if it were getting a lower angle on the edge 16 degrees per side or less. Because these steels are already pretty tough, a higher angle plain edge won't benefit from a micro-bevel, but a lower angle edge will wear down very quickly due to there not being enough metal behind it to retain its stability.
Now why would I choose to put a lower angle edge on a tough, but not particularly hard edge like that? Its the thickness behind the edge that makes that decision for me. If I have an S30V knife which is 0.050" right behind the bevels. I'm going to need to put a relatively narrow angle on that to make it any kind of decent slicer, but if I do that, it will dull down very quickly because there won't be much width right behind the apex of the cutting edge, so I will need micro-bevel to make this edge last. But who says it needs to be a great slicer? What if this is going to be a well abused camp knife? In that case, I'm going to go up to 24 degrees per side, leave it at 600 grit finish, and call it good because what I want is toughness and edge stability above all else.
What if this same knife was only .015" behind the cutting edge and I knew it wasn't going to get any hard use? In this case, I think the best move would be to set the bevels at 18 or 19 degrees per side because I don't need to worry too much about toughness or stability, the steel is already pretty tough and strong. What I need to worry about here is simple slicing longevity, and that means I want to polish my edge because that does have a big impact on edge retention once hardness is above about 58-59 HRC. I could choose to add a micro-bevel, and it might make the edge last a slight bit longer, but it might not either.
So you begin to see how I apply these four considerations when choosing an angle, finish and micro-bevel. What about these super hard steels though? With these steels, my main concern is toughness. The very thing they lack. I don't want to give a blade back to a customer without taking every step I reasonably can to make sure that it won't chip or crack on the edge. Because toughness is my main concern and the purpose of a micro-bevel is to improve edge toughness, I will always apply one to very hard and brittle steels like Maxamet or REX121. Because I already know I will be using a micro-bevel, I'll go down as far as 12 or 13 degrees per side on the edge bevels as log as its thick enough behind the edge of the knife. (.020" or more)
This brings me to another point about micro-bevels. Whatever you polish your main edge bevels to is also what you should polish your micro-bevels to. If I have an abused camp knife made out of a harder steel (why a maker would do this is another matter) I would leave it at 600 grit because It needs to be toothy to rip through things. Then I would also leave my micro-bevels at 600 grit because i want the apex of the micro bevel to be the same width as it would be without. Not so critical for a camp knife like this, but very critical in the manix 2 in maxamet above. if I were to polish the edge bevels up to 3 microns (I don't really see much point in going beyond that, diminishing returns and all) then that is going to give me an apex which is only about 0.15-0.1 microns wide, this is where an edge will cut a free hanging hair under the hair's own weight. If I want that level of sharpness, but I leave the micro-bevel at 1000 grit diamond stone finish, then the actual apex will be much wider than that and will not cut these hairs. If I want that ability, then I need to take the micro-bevel all the way up to where I finished the edge bevels. For this reason, whenever I put a hanging hair edge on a knife like those above, I will also finish the micro-bevels up to that hanging hair sharpness.
This brings me to my last comment about steels in a generality. Steels like Bohler-Uddeholm M390 and its twins (Carpenter CTS-204P and CPM-20CV), S110V, Sleipnr, and a handful of others are excellent "Jack of All Trade" steels. One can put just about any edge of any description on these steels and they will be good to go. You can have a thin cross section behind the edge of a CTS-204P like on this Spyderco Military sprint run, and you can put a very wide angle or a very narrow one, and it will just smile and hold that edge nicely. You can also have a thick-behind-the-edge blade of Sleipnr, like on my Lionsteel SR11B, put a very narrow 12 degree per side edge bevels and it will take it and hold it like a champ.
