Little help Cliff. What's the best way to sharpen Dendritic steel?

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T. Erdelyi

T. Erdelyi

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I have a Boye Prophet with dendritic steel, what's the best way to sharpen it with an EdgePro.

I recall someone said that because of the way the carbide molocules are suspended in the matrix I shouldn't sharpen to a polished edge, so at what grit do I stop to maintain a long lasting aggresive edge?

Cliff if you can help here I'd appreciate it.
 
Jeff thanks for the link I lost a lot of my links when my computer crashed a month ago, now I have Cliff's link in my favorites again.

Once again, thanks Jeff and thanks Cliff.
 
You should have received an instruction booklet with your knife. David Boye doesn't use boxes, but each plastic bag with his knives has his pamphlet with knife care and sharpening instructions.

David Boye says to sharpen it at the same angle as the blade is ground. He says use a coarse or medium grit stone. I don't know where jeff clark is coming from, but Boye says diamonds are too generally too aggressive and will wear out your edge too quickly.

Note the above link appears to be to an article on dendritic cobalt, you indicated that your blade is dendritic steel. I only have the dendritic steel blades and the instructions I related came with all three of my knives. I have never seen his instructions for dendritic cobalt.
 
I remember a conversation I had at the ECCKS with someone and they said if you use a diamond hone use a medium hone, I believe the problem with diamond was that it wore away the carbide because the diamonds were harder, where as a regular hone would leave the carbide exposed while wearing away the softer material leaving a very aggresive cutting edge exposed.
 
Cliff's review was of denritic-440C stainless, dendritic-cobalt, and fine-grained AUS-8 stainless. One thing it showed was that with a 600 grit diamond hone the dendritic-440C would slice very aggresively for a very long time. This would seem to undermine Boye's assertion. Almost every knifemaker says that diamond hones will wear out their blade too fast. That's BS. I have used diamonds a lot and they don't remove any more material than you make them remove. There is a rather fixed amount of material that has to be removed at any given time to restore an edge. You get there faster with diamonds. The trick is to stop at that point.

If you want a contrasting method for sharpening dendritic steel, try around 400-600 grit Silicon Carbide paper (such as 3M Wet or Dry Paper). Hone very lightly to avoid rounding the edge. Finish by stropping, edge-trailing, on the paper on a semi-soft backing surface like a stiff mouse pad.
 
As Jeff noted its nonsense. The speed of an abrasive is much more strongly determined by its grit not what it is made out of. A x-fine diamond stone cuts *SLOW* compared to a coarse waterstone. Plus oversharpening is a problem with method not stone, you can oversharpen with a 8000 grit waterstone if you don't know when to stop. Test the edge periodically and stop honing when it is sharp and you won't have a problem with oversharpening regardless of the abrasive.

As for not cutting the carbides and just cutting the steel, that is nonsense as well. Just consider if this was true, then you could not shape a Dendritic blade with an AO abrasive, which is trivial.

Specific to Dendritic steel and Cobalt, what is *critical* is that they are very soft and decently wear resistant, thus you need to use a stone which is inherently very aggressive and thus uses the least amount of force to cut.

This is necessary because when you apply high forces to soft steels the edge deforms readily and weakens. Thus the best method for sharpening them is a wide Diamond pad of suitable grit.

Boye sets his edges very thin (0.005-0.010") so it should sharpen up very quickly even if you don't match the initial angle, which there is no reason to, you grind that suitable for your work, and your method of sharpening.

If you want to use rod based sharpeners, use them only to set the final edge, have the primary edge ground thinner, and if at all possible use the flats of a triangle rod like the Sharpmaker. If using rods, then use Diamonds and go *light*.

Again as the materials are *soft* [the cobalt is ~35 HRC], you want to keep the force down so that the edge is cut rather than just squished.

-Cliff
 
Or you can follow the manufacturer's instructions. I do and it works. Boye actually "wrote the book" on knifemaking or at least one of the first. Maybe you all have made a few thousand knives and thus are experts? :) Boye's instructions are for the public who could very easily ruin an edge with a diamond hone when a simple $10 arkansas medium or coarse stone would do. Personally, I buy Boye knives for the fine edge, one of the best in the business, IMHO, only a fool would reprofile one of his blades.
 
I may not have "made a few thousand knives", but I have reprofiled a few thousand knives over the last 45 years. I started doing it before Boye started making knives. I have his book and I was disappointed. I will happily reprofile just about anything if it suits my purpose. I have wrecked enough knives to have a clear idea of the consequences of my modifications.

One of the things that I have played with for at least the last 40 years is the effect of intensionally giving a rough finish to knives that are intended for slicing meat or slashing. Back in the mid-60's I was playing with file edges to milk performance out of bayonets and cheap switchblades. When Boye gives instructions intended for the ignorant masses to follow I don't presume that he intends to preclude adjustments by more sophisticated users. I don't assume that he necessarily restricts himself. Even within the limits of "coarse or medium grit stones" you can get diverse edge finishes depending on whether you use aluminum oxide, silicon carbide, oil stones, water stones, or dry stones. I know that if I am trying for a good slicing edge I will use a hone with a sharp grit profile. Diamond is one of the best you can find. After that I would tend to look at a water stone. As I said before, you might even want to try honing and stropping on new silicon carbide paper, since the grit is fresh and sharp on the paper.
 
I think the "diamonds are too fast" may be just dated. Maybe when this was decided you could only get really rough diamond stones. It certainly doesn't apply now with Diamond hones being far finer than any India stone.

Crap I thought I had reprofiled a decent amount of knives but I have not made it significant past a few hundred.

Count me as a fool though as I would readily reprofile a Boye edge as I run my edges more acute than he grinds them for that style of knife (not thinner, more acute).

Note if you want to try out a Boye style edge, Fallkniven is running their knives now with edges that are that thin. The U2 and H1 I have used have high grinds and edges ~0.005 - 0.010" thick, just barely visible (as a side note they recommend Diamond to set the edge).

Phil Wilson runs the same profile as Boye, but on thinner blade stock and runs the steels *much* harder and uses many CPM high alloy steels (he also recommends Diamonds to set the edge).

Alvin Johnson runs edges as thin, much more acute still and harder even than Phil. You can't really reprofile Alvin's thinner as they are ground flat to the spine. So to thin out the edge you would have to hollow out the primary. I don't think he would call you a fool if you did that though, he would most likely ask to see a pic of the knife and ask you how you did it, and if you liked the result.

-Cliff
 
clark, you've re-profiled a lot of knives, but they probablly weren't dendritic steel. but clark, you hate 440C steel, so i don't imagine you have any dendritric 440c or do you? i am ignorant of metallurgy, but do know a bit about materials science. just enough to be dangerous. but that dangerous amount would lead me to ignorantly suppose that if dendritic truly has a more crystalline stucture than normal 440c steel, then a finer edge may chip more. it also me be more prone to wear from some aggressive diamonds.

cliff you are right, the diamonds being sold now are not the same as a few years ago. even some of the big players have changed their offerings and they've gotten cheaper
 
A Boye Prophet Companion was my first pocket clip folder, a gift from my wife after graduation. After about 2 years of hard use and almost daily metal removal sharpening, I finally wore it out. Actually, it would still work, but the edge was about 1/8" back from its original location. Only at this point did I start using diamond stones on it. I used a 325 grit DMT (blue) to reprofile it, with no ill effects. To my surprise, the edge also did not chip, despite the rough treatment I gave it. I kept it sharp enough to shave strips from annealed steel wire (tie wire for rebar) and this didnt seem to dull it after 2-3 strips. I used nearly everything to sharpen this knife, from $5 AO stones, to DMT, to 80 grit belt on a 1x30 sander. If I can sharpen it with that, then there is no need to worry about diamonds cutting too fast. I used an Arkansas stone for a while, but found that it cut too slowly.

The point is, I like this knife alot, and all the above methods gave good edges. I believe the Edge Pro uses water stones. I just recently started using water stones, but if there is a stone in the 600-800 grit range for the edge pro, that should work fine. My 800 grit stone gives my kitchen knives an aggressive edge that will shave hair with a slicing motion (not recommended, but I havent cut myself yet).

The stated purpose by the maker for using a cast steel is that the carbides (presumably Chromium Carbide) that form are fairly large and are quite aggressive. It's probably safe to assume they are fairly evenly distributed, although finer carbides in the same volume amount would be more so. I read somewhere (I think it was from Cliff) that occasionally, an abrasive should be used that will cut the carbides, ohterwise there will be dull carbides along the edge of an otherwise sharp blade. If the sharpening abrasive wont cut them, then they will just become rounded and will tear out as the steel around them is worn away. This is why every so often I used my DMT or some SiC sandpaper on my 440V Random Task, just to sharpen the carbides and get some good bite from them.
 
As an aside, I owned two Boye dendritic knives and the blades of both of them snapped just from slicing - both about 1/4" from the tip. That's a pretty small sample but it was 2 for 2 for me. If I had another one, I'd use a fairly obtuse bevel angle since I consider them to be delicate.
 
brownshoe, funny you should ask. I do have a Boye 440C dendritic blade. I bought it as a finish-it-yourself kit blade. I got it as part of a search for an ultimate hunting knife. The problem was that it just wasn't a general enough solution for my hunting knife needs. I want something that will handle my full field dressing process. The dendritic 440C is great for skinning, but it isn't great when you need to split bones. It is a bit on the brittle-side for that application and the bone tends to smooth out the edge micro-serrations.

Did you know that you can get dendritic D2 blade blanks? This might work a bit better. My only rough edge hunting knife at the moment is a rather long L6 blade that has a smooth edge near the base for bone splitting and a rough finish for the remainder of the blade. The L6 is really tough, but I don't like the smooth edge that I get on it. The rough finish slices better. I wonder if there could be such a thing as dendritic L6 or S7?
 
Jeff you can make any steel really coarse grained just by oversoaking it (too high a temp, or too long a time), or tempering at really high temps (this is exactly why blades get soft at high temps the carbides coarsen). This will give you a massive grain structure with huge carbides in a very soft steel matrix.

Usually this isn't a good idea as its better to make the steel inherently strong and tough and get the slicing aggression from the grit finish, blade profile. If you want an aggressive slicing finish the best I have found is an unbuffed 100 grit AO belt finish. This leaves micro-serrations large enough to almost be visible. The edge retention is many times longer than something like the Spyderco medium stones on ropes and such.

As for the dendritic steel wearing faster on diamonds this would mean that it has a high machinability, this would be a good thing as it means you don't take as long to sharpen. If for some reason you want to take a long time then :

1) make a pass with the diamond stone
2) put the stone down, do a back flip
3) repeat

As for the steel being brittle, yeah, its also soft too so you get the worst of both worlds in regards to durability, they do cut well though in general I would prefer a harder steel in the same profile, but I would not be upset if I had one of Boyes blades to depend on for such work.

-Cliff
 
Cliff, There is a claim that the shape of the carbides in a "dendritic 440C" blade is a bit more optimal than simply having large carbides due to over-cooking the heat treatment. The "dendritic" reference produces images of frost crystals on windows. Are you skeptical of the validity of the designation?

PS: T. Erdelyi, sorry if we have sort of hijacked your topic. On an Edge Pro I would use a relatively coarse hone with the sharpest grit posible. You want to remove material and leave grooves in the edge. A water hone would be very good. If you use a dry or oil stone, scrub it first with sink scouring cleanser and a hard brush to expose fresh grit on the surface of the hone.
 
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