CBN Stones?

C

cm_bushman

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Oct 22, 2012
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I've been researching CBN compounds and sprays lately and after a little searching, I've not been able to locate a CBN based sharpening stone (other than some poorly-described and oddly shaped examples on Ebay).

I don't see any reason that CBN wouldn't be used, I wonder what its scratch pattern would be like. It may be the "missing link" between traditional SiC and AlOx stone finishes and diamond's speed and agressivness, with the ability to abrade fine carbides.

What do you guys think?
 
For sharpening by hand (unpowered, in other words), I don't think there's much incentive for manufacturers to make CBN stones. I think Spyderco is experimenting with it, as an alternative to their ceramic hones or diamond rods (see link below). Otherwise, CBN is generally known to be more complicated to produce, and therefore more expensive, than diamond abrasive products. When used by hand, diamond will accomplish anything CBN can, so there's not much reason to push a line of CBN stones. CBN's largest advantage is for powered grinding media (wheels, belts), because it remains more stable at the high temperatures generated by powered grinding, and is also non-reactive. Diamond loses much of it's hardness at high temperature, and also reacts chemically with the iron in steel at those high temperatures, with bad results.

http://www.spyderco.com/forums/showthread.php?63254-CBN-Rods

On the note of diamond being too aggressive, my usual 'fix' for that is simply to use a finer diamond grit for jobs that would ordinarily be done with coarser grits in abrasives like SiC or AlOx. It's rare when I need anything more than a Fine or EF diamond (600/1200 mesh, or 25/9µ) for folder-sized blades in any steel, and perhaps nothing more than a Coarse diamond (325 mesh, or 45µ) for anything heavier. I've almost never used my XC diamond, and haven't found a need to use an XXC at all.


David
 
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It (CBN) spanning the gap between SiC and diamond. Can it be produced economically? Attractively priced for the consumer in a hand stone. Not as today's mfg.. DM
 
Thanks for the link Obsessed. CBN still seems hard enough that the differences between it and diamond are such that for hand sharpening, it is still too agressive to get the same level of finish as SiC in the lower-medium grits.

I was hoping for a one-size-fits-all solution, but I should have known better. I still love the CBN emulsions though!
 
cm_bushman said:
Thanks for the link Obsessed. CBN still seems hard enough that the differences between it and diamond are such that for hand sharpening, it is still too agressive to get the same level of finish as SiC in the lower-medium grits.

I was hoping for a one-size-fits-all solution, but I should have known better. I still love the CBN emulsions though!
Click to expand...

I was just taking a longer look at the Spyderco thread I linked. In terms of aggressiveness, it looks as if Spyderco's CBN rods (at ~40µ) are every bit as aggressive as a similarly-rated diamond, at least as used on comparatively soft (by any measure) steel knife blades. There's a video, linked in post #64 of that thread by the thread's author (Cliff Stamp; former BF member), showing how he uses them on the Sharpmaker, and he leaves no doubt as to the importance of keeping pressure extremely light. Based on how it appears he's using them, it would seem to compare closely to using a Coarse diamond from DMT (45µ) for the same thing. In other words, the slight differential in hardness, between CBN and diamond, is less a factor than the size of the grit itself. As compared to knife steels and the carbides in them, either can be viciously aggressive (so it appears). And that doesn't even account for differences in grit shape as well, which can make big differences in aggressiveness. I seem to recall reading that because CBN is entirely man-made, it can also be 'tailored' to certain shapes as well, within limits. That might give it an additional advantage over diamond, in 'shaping' the abrasive grit to tailor it to specific uses. But again, that's one more thing to make them that much more expensive to produce. ;)


David
 
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Well lets explore the matter slightly more in depth.

There are three types of diamond:

Monocrystalline Diamond (MDP)
Polycrystalline Diamond (PDP)
Natural Diamond (NDP)

So whats the difference?

Monocrystalline diamond is cheap to produce (relatively speaking) and its still diamond. Making it quick to cut even the most ridiculous of steels and even ceramics. However it has a blocky shape with few cutting edges. This makes it slower than other diamond types but at less than half the cost to produce its a even tradeoff for things such as diamond plates and films.


Polycrystalline diamond is quite expensive to produce , and as a result is often overlooked when discussing sharpening abrasives. However it has many times the number of cutting edges than Monocrystalline and Natural Diamonds. This results in faster cutting. I find it also leaves a "stickier" edge when compared side by side to monocrystalline preparations.



Natural Diamond is not discussed at all for sharpening , in fact I don't know of anyone who has used the stuff to sharpen with. It is quite costly even more so than Polycrystalline and does not offer any advantages over Polycrystalline , but does however have more cutting edges than Monocrystalline. I also suspect that a Natural Diamond prepration would have a poorer particle size distribution compared to the other variants. Typically Natural Diamond is used in the gem/diamond polishing markets but it is also used for general lapping and polishing applications. Larger crystal NDP is used for single point tool applications and in some cases for diamond die applications.



So if you have read thus far you may be wondering where Cubic Boron Nitride (CBN) falls into all of this. CBN has a polycrystalline structure , meaning it has more cutting surfaces (comparing equally sized particles remember) , than its Monocrystalline and even Natural Diamond counterparts. It falls in between Monocrystalline and Polycrystalline diamond for cost , and poses a close second to Polycrystalline in terms of performance. CBN is the second hardest substance (next to diamond) and is harder than diamond in high temperature applications. Allowing it to cut even vanadium rich steels with ease.


So why don't we see sharpening stones with CBN mixed in? Because you can just add a drop of a CBN stropping compound onto your waterstone to enhance its performance and allow it to cut even the most exotic steels with ease.

For more information about PDP , MDP , CBN and particle size distribution , check out this this blog.
http://www.precisesharpening.blogspot.ca/2010/12/part-1-comparison-of-three-quarter.html
 
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Interesting, thanks. So, you could add a drop of CBN to any stone and enhance it's performance. Does Norton sell the CBN slurry? Still, one can do this with diamond slurry as well. Which is what many of us have been doing for sometime. DM
 
I just nabbed a 200ml bottle of the Buehler water-suspended .05 micron poly diamond from eBay. Not sure of the concentration but I'll let you know how it works if interested. Mono and poly are slightly different in terms of finish - this can be very dependent on the "carrier" though. On harder surface there is more of a difference, on leather or similar surfaces less so.
 
eKretz said:
I just nabbed a 200ml bottle of the Buehler water-suspended .05 micron poly diamond from eBay. Not sure of the concentration but I'll let you know how it works if interested. Mono and poly are slightly different in terms of finish - this can be very dependent on the "carrier" though. On harder surface there is more of a difference, on leather or similar surfaces less so.
Click to expand...

0.5µm? going for the mirror shine huh? I do use 9µm-3µm-1µm stepping; paste from the syringe and mix with water on a woven cloth/short piled carrier.
 
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