DMT paste vs CBN spray, which one is better?

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knife chop

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Feb 11, 2014
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With all these hard, high wear resistant steel i find myself looking for a better strop compound. Don't get me wrong, i still strop an S90V on a white and green compound from stropman but i find it to be time consuming. but using a DMT or CBN, will it speed up the process and will it refine a high wear resistant steel better than compounds? Thanks
 
Yes it will noticeably speed up the process. I can't comment on the comparison between the DMT paste and a CBN spray as I don't have both, but I can say I sometimes find the DMT paste a little difficult to apply. Being a paste, it can be hard to get a uniform, thin coating on the strop and I often end up wasting a bit of the paste. Not much is wasted but the stuff is expensive. A spray should be easier to apply. Cubic boron nitride is going to be a little bit softer than diamond but I don't think it will make a huge difference since it's steel you're abrading. IIRC they have the same crystal structure so the particles they form should be of similar shapes, so they should abrade your steel similarly. The particle sizes in a good spray should also be more uniform than a stick of chromium oxide and possibly give you a better finish.

If it helps, laboratories normally use diamond sprays for very fine polishes.
 
knife chop said:
35 views and no opinions?
Click to expand...

That is because you are in the wrong section:
General Knife Discussion is for discussing knives themselves
Maintenance, Tinkering, and Embellishment is for discussing sharpening (aka maintenance).

Let's see if we can get this moved...
 
Both diamond and CBN will work on high vanadium-content steels. CBN is roughly half or two-thirds as hard as diamond, but still easily harder than vanadium carbides, nearly by a factor of ~2 or so. Biggest difference between the two is that CBN is much more stable at very high temperatures (of the kind found in industrial powered grinding operations). Diamond is known to break down and lose hardness in powered grinding operations, if/when it gets very, very hot (I think it's upward of 800°C). Very important for such operations to be done using liquid coolant. CBN remains more stable at these very high temps, so it's being utilized more in industrial grinding wheels & belts, for this reason, over diamond. All that said, neither one of these is going to get nearly as hot in use on hand-driven sharpeners/strops, so no worries about either one breaking down.

Vanadium carbides are usually at least slightly harder than either SiC or AlOx abrasives. Due to the relatively small size of vanadium carbides (individually) in PM steels, usually in the 2-4 micron range, diamond/CBN may not be needed if finishing/sharpening at relatively coarser grits. If wanting to take the finish to mirror levels using abrasive grit that's <5 microns or so, the vanadium carbides will start to resist weaker (softer) abrasives likel SiC or AlOx more at that level of finish, so it'll be harder to refine them. That's where the harder diamond/CBN will offer a bigger advantage. A coarser edge finish at maybe ~10 microns or more won't necessarily need to refine individual carbides as much, so the surrounding matrix steel (much softer) will respond to somewhat less-hard abrasives.

By decreasing order of hardness:

  • Diamond = hardest of all
  • CBN (Cubic Boron Nitride)
  • Vanadium carbide (found in high-wear CPM steels like S30V/90V/110V/etc.)
  • Silicon Carbide (a.k.a. 'carborundum'; these are 'black' compounds)
  • Aluminum Oxide (a.k.a. 'alumina'; man-made, these are often 'white', but may also be brown, grey, blue, pink)
  • Emery (a.k.a. 'corundum', which is naturally-occurring aluminum oxide; often brown in color, maybe grey/nearly black)
  • Chromium Oxide (a.k.a. 'green' compound)

( I've been reading lots of cool stuff about these lately, so the above is something new I've learned as well. :) )


David
 
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Obsessed with Edges said:
Both diamond and CBN will work on high vanadium-content steels. CBN is roughly half or two-thirds as hard as diamond, but still easily harder than vanadium carbides, nearly by a factor of ~2 or so. Biggest difference between the two is that CBN is much more stable at very high temperatures (of the kind found in industrial powered grinding operations). Diamond is known to break down and lose hardness in powered grinding operations, if/when it gets very, very hot (I think it's upward of 800°C). Very important for such operations to be done using liquid coolant. CBN remains more stable at these very high temps, so it's being utilized more in industrial grinding wheels & belts, for this reason, over diamond. All that said, neither one of these is going to get nearly as hot in use on hand-driven sharpeners/strops, so no worries about either one breaking down.

Vanadium carbides are usually at least slightly harder than either SiC or AlOx abrasives. Due to the relatively small size of vanadium carbides (individually) in PM steels, usually in the 2-4 micron range, diamond/CBN may not be needed if finishing/sharpening at relatively coarser grits. If wanting to take the finish to mirror levels using abrasive grit that's <5 microns or so, the vanadium carbides will start to resist weaker (softer) abrasives likel SiC or AlOx more at that level of finish, so it'll be harder to refine them. That's where the harder diamond/CBN will offer a bigger advantage. A coarser edge finish at maybe ~10 microns or more won't necessarily need to refine individual carbides as much, so the surrounding matrix steel (much softer) will respond to somewhat less-hard abrasives.

By decreasing order of hardness:

  • Diamond = hardest of all
  • CBN (Cubic Boron Nitride)
  • Vanadium carbide (found in high-wear CPM steels like S30V/90V/110V/etc.)
  • Silicon Carbide (a.k.a. 'carborundum'; these are 'black' compounds)
  • Aluminum Oxide (a.k.a. 'alumina'; man-made, these are often 'white', but may also be brown, grey, blue, pink)
  • Emery (a.k.a. 'corundum', which is naturally-occurring aluminum oxide; often brown in color, maybe grey/nearly black)
  • Chromium Oxide (a.k.a. 'green' compound)

( I've been reading lots of cool stuff about these lately, so the above is something new I've learned as well. :) )


David
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Thank you for the detailed and educational response. with that i have a few more questions. why is CBN more pricey than diamonds if essentially both will work on steels with high vanadium.

i have a spyderco southfork and a GSO 4.1 in cpm 20cv. what's a good or general micron size for just stropping? i'm not looking for a polished edge. i just want to keep them hair popping sharp after camp tasks. and is it necessary to get a kangaroo leather?

lastly, will a diamond or CBN eat up a 1095 steel quickly when used to strop?
 
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CBN should only be slightly more expensive (lol - big markup from sellers). CBN manufacturing require industrial high energy/pressure process, whereas diamond can easily be made from explosion - could even be by-products of explosions from mining.

For sharpness stropping, I use cbn/diamond abrasive sizes 12um and 0.25um. For lapping/polish (for look), I use 12,8,6,3,1,0.5,0.25,0.1um.
 
A 6 micron would be nice on a harder strop such as balsa wood. A strop is not a aggressive metal removal tool it's only to polish. I would stay above 1 micron unless you are honing razors.
 
Obsessed with Edges said:
Due to the relatively small size of vanadium carbides (individually) in PM steels, usually in the 2-4 micron range, diamond/CBN may not be needed if finishing/sharpening at relatively coarser grits. If wanting to take the finish to mirror levels using abrasive grit that's <5 microns or so, the vanadium carbides will start to resist weaker (softer) abrasives likel SiC or AlOx more at that level of finish, so it'll be harder to refine them. That's where the harder diamond/CBN will offer a bigger advantage. A coarser edge finish at maybe ~10 microns or more won't necessarily need to refine individual carbides as much, so the surrounding matrix steel (much softer) will respond to somewhat less-hard abrasives.

By decreasing order of hardness:

  • Diamond = hardest of all
  • CBN (Cubic Boron Nitride)
  • Vanadium carbide (found in high-wear CPM steels like S30V/90V/110V/etc.)
  • Silicon Carbide (a.k.a. 'carborundum'; these are 'black' compounds)
  • Aluminum Oxide (a.k.a. 'alumina'; man-made, these are often 'white', but may also be brown, grey, blue, pink)
  • Emery (a.k.a. 'corundum', which is naturally-occurring aluminum oxide; often brown in color, maybe grey/nearly black)
  • Chromium Oxide (a.k.a. 'green' compound)

( I've been reading lots of cool stuff about these lately, so the above is something new I've learned as well. :) )


David
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Thank you David for putting this rather complex topic into a better understandable package. With my lack of knowledge I concluded in my naivety, that smaller abrasive structure in compounds, equated to a finer polished edge. That could be true depending on the steel but with the &#8220;super steels&#8221; available today, what may have been more accurate 20 years ago or so just isn&#8217;t today.
It seems like an equation of some sort exists here. Compound abrasive size; abrasive hardness; steel; and desired finish. Not necessarily in any order.
So again, thanks for sharing with us and please, anyone, refine what I&#8217;ve said here to be more accurate. Remember&#8230;laymen like myself hang out here :).
 
knife chop said:
Thank you for the detailed and educational response. with that i have a few more questions. why is CBN more pricey than diamonds if essentially both will work on steels with high vanadium.

i have a spyderco southfork and a GSO 4.1 in cpm 20cv. what's a good or general micron size for just stropping? i'm not looking for a polished edge. i just want to keep them hair popping sharp after camp tasks. and is it necessary to get a kangaroo leather?

lastly, will a diamond or CBN eat up a 1095 steel quickly when used to strop?
Click to expand...

Bluntcut pretty much covered reasons for differences in cost. Odd as it sounds, diamond (for industrial purposes) is much more easily sourced, either as by-products of mining/milling/grinding of 'natural' diamond, or as a synthesized product (process has been done for decades). CBN is entirely man-made, and the process for doing so is pretty complex. Harder to make in volume, so prices will be higher.

AND, I'm betting Jason's (knifenut1013's) recommendation for stropping 20CV is likely knowledgable too. I've never tried or used 20CV, so I won't speculate. In general terms, for high-wear steels with significant vanadium carbide content, I've always liked 1µ diamond compound (I use paste). Although more and more, I'm finding some of these steels are just about perfect coming straight off something like a Fine/EF diamond hone (DMT), with little or no stropping to follow.

I'm pretty biased about 1095 steel, regarding stropping. I don't generally like to use more aggressive abrasives for it, like diamond or SiC (I wouldn't use CBN for it, either). 1095 is very, very easy to over-strop with these two compounds. 1095 has basically no wear-resistance (no carbides at all) as compared to the CPM-type steels. So, harder abrasives will eat it up fast, regardless of particle size. Aluminum oxide (usually a 'white' compound) or chromium oxide work GREAT for 1095, so I've had no desire to mess with anything else on this steel.


David
 
Well there's some good information in this thread - and some misconceptions. So let's go through this.

So there is diamond and CBN and boron carbide. Diamond can be divided into monocrystalline and polycrystalline. I'm simplifying this, ignoring natural diamond , various other forms used in embedded products, etc.

Of the three, monocrystalline is the least expensive, polycrystalline the most expensive and CBN inbetween. Boron carbide is less expensive than these. Aluminum oxide, and silicon carbide and emery are much less expensive, available by the pound vs the other abrasives available by the carat (1/5 gram).

Obviously compounds that are more dilute cost less. Compounds that hide their concentrations are - not surprisingly - more dilute.

Compounds that are more precisely graded cost more. If your compounds are not precisely graded for the specified size AND vary a lot as well, they are cheaper and perform poorly. If the compound is pure - it costs more. Those with contaminants cost less. Bars of compounds are particularly poorly specified - you can't even get information about what's in them! So green bars MAY contain Chromium oxide, aluminum oxide or some mix and the two components not necessarily matched for particle size.

Compounds can be dried powders, or in various formulations. Brewing your own mix from powder is a near guarantee of getting particles stuck together (agglomeration) acting like larger particles and giving you stray scratches. Doing this right takes considerable effort. If you want to compare this, think of the powder like steel and the formulated compound like a well tempered knife made from the steel. There is considerable art to producing a well formulated compound.

The formulations can be water or oil soluble. They can be slurries or suspensions. Suspensions can be water or oil soluble. So for instance you can have a suspension that has multiple components, can be a gel type formulation, emulsion formulation, paste formulation etc etc. These formulations can be adjusted to a specific viscosity. So for instance the DMT pastes spread on a strop with difficulty and my emulsion formula spreads easily on leather giving a uniform application with almost no wasted compound on leather or nanocloth or even waterstones. They can be formulated for a specific task - eg knife sharpening, ability to adhere to a powered belt or certain type of bench strop etc. Sometimes they are formulated badly with no concern for any of these and the suspension components separate etc. Suspensions also need to be formulated differently based on the particle size and characteristics. So heavier particles are harder to keep in suspension. Think of designing a dump truck suspension vs a Porsche suspension - very different requirements. Surface tension and electrostatic forces are dependent on particle sizes and this too needs to be considered for a high quality product.

Diamond arecmade for these types of applications through explosions - at much higher pressures than seen in mine explosions under carefully controlled processes. Once made they are graded sized and processed to specification for grit size. As you can imagine, the quality of this grading is more expensive when more precisely done.

Polycrystalline diamond is quite expensive but superior to monocrystalline for some applications. Polycrystaline is made of multiple crystals fused together (that's why it's called poly :) ). So for a given particle size you have MANY sharp points compared to just a single crystal. This gives you more cutting action, more consistency of cut and a degree of friability that keeps sharp cutting edges exposed. Best for a slurry or emulsion (IMO). Monocrystalline breaks down less, so it is best where the particles are embedded in a lapping plate within a nickel matrix or resin matrix, giving you less fallout but points more easily dulled. Better costs more.

(continued - exceeding single post size limit)
---
Ken
 
(continued from previous post)


David (obsessed) has lots of good info in his posts. You can rate hardness of these abrasives using the Moh's scale - a nonlinear scale of relative hardness. CBN and diamond (mono and poly) are harder than vanadium and niobium carbides. CBN is very close in hardness and has other desirable characteristics both for high speed grinding and for use on strops. Boron carbide is a bit softer and the others fall below that. This makes diamond and CBN excellent for abrasion resistant steels. They also work fine for less abrasion resistant steels, working faster, but not eating them up. Abrasion rate is related more to particle size and density. There is some interactivity with diamond and the carbon content of steels for powered grinding application that you dont see with cbn, making CBN more desirable for powered applications. I don't consider this advantage critical for most knife sharpening applications.

Grit size obviously plays a role in determining effect. You most certainly CAN create a burr with coarser CBN, eg 16 microns and above and also at lower grits, especially with powered applications. I have people using 80 micron CBN following a 220 or even 120 grit belts for instance to good effect. Using a sequence of strops, you can go from a dull edge to a sharp one without stones.

Even at 16 microns or 1k grit, you can produce a very nice edge. At 4 microns (4k) you will have an edge significantly sharper than the edges seen on most all production knives and many custom knives. At 2 microns (8k) it starts becoming impressively sharp. From there the superlatives just increase. For instance I routinely strop at 3/4 micron or 24k on my kitchen knives. The idea that you are limited to a 6k edge for a high performance edge for kitchen knives is just not correct. In fact once you get past a coarse edge you start getting both increased bite and push cutting performance. It is not unreasonable to combine edges produced with natural stones with stropping with compounds for superb kitchen edges. Or stopping earlier. This is a large topic in itself, but the idea of 'running edges' and other reasons for stopping at a coarser edge for all applications is one I dismiss. Of course this is steel dependent with some knives not capable of this level of performance. High grits alone are not a panacea - it needs to be done precisely respecting basic knife geometry.

Hope this is of use. Let me know if I can answer any more questions, either here or by PM etc. I know I didn't cover everything in great detail. I guess you could say I barely scratched the surface :)

---
Ken
 
knife chop said:
..... and is it necessary to get a kangaroo leather?
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No. In fact, it's not necessary to use leather at all when using compounds. Any firm substrate will do.

When using compounds, any 'firm' leather will work equally well. (The operative word here is 'firm.') If the kangaroo leather is vegetable tanned, you can case it just as you should a piece of veg-tanned cowhide. If the leather surface is too soft, the pressure of the blade will press down and allow the leather to curl up around the edge, creating a convex edge. The firmer the leather, the better. Shell Cordovan Horsehide is the very best for use without compounds, but a properly processed (cased) cowhide will be almost as good, and quite fine for use with compounds. No need for expensive leather if you are using compounds.


Stitchawl
 
Ah I knew there was something I didn't address in my last posting :)

Do you have to use a Kangaroo leather strop with CBN? Absolutely not. I use CBN on other leather - horse, cow, even tried goat. You can also use it on Balsa or the wood of your choice. I also use it on nanocloth too with excellent results. It is also useful to use it on paper as a substrate.

Even a firm substrate is not an absolute requirement, depending on what you wish to achieve. While a hard substrate is ideal for a flat grind and you can do convex edges on a hard surface, a somewhat softer surface is easier to use on convex grinds and actually an advantage on a more irregularly shaped surface like the front of a single beveled yanagi.

You can even use it on stone surfaces, both natural and synthetic stones. Stones that generate more mud provide a softer surface with a mud 'cushion' and work best on irregular surfaces. For Hamaguri grinds ( convex front bevel), the softer stones work best - like a 1200 Nubatama or an Aoto or Hakka for instance. On harder surfaces like the 1k Speckled Ume or Shapton Pro stones or Nakayama Asagi, the edges are more precise but less forgiving and these work best where angle variation is kept to a minimum - like straight razors.

The surface characteristics of the substrate are important as well. At coarser grits, this is less critical so you can use balsa, copy paper and cow hide. Horsehide is a bit finer surface and Kangaroo is the finest in terms of leather surface characteristics, providing minimal abrasion characteristics of its own to interfere with compounds. Using a test of whether or not a fingernail will temporarily 'dent' a leather surface is a useless criteria, since the amount of force used in pounds per square inch is never anywhere close to that level of force. Here thinness is a more significant advantage. Stitch and I disagree on this point, with Stitch feeling that this is a useful criteria. I have absolutely no problem convexing my edges inadvertently on Kangaroo mounted on a hard backing. The results are limited by technique. Kangaroo leather used on an Edgepro or Wicked edge paddle produces extremely flat results, verified with micrographs. Here the angle variations are minimal. Nanocloth has no perceptible abrasive characteristics of its own, so the compound effect is purest using nanocloth. If you are using paper for the finer grits, I prefer fine writing papers like Rhodia, Clairfontaine and several Japanese papers and Bagasse papers (this paper is made from sugar cane pulp) and even Crane brand cotton based paper. The paper doesn't hold up as long but is particularly useful to use in smaller pieces much like traditional fingerstones.

CBN can also be used on leather belts, felt belts, felt wheels, and linen belts. For powered applications, I prefer using an emulsion formulation, however some prefer an oil based paste formulation, as these both give better particle adhesion to the substrate than the gel suspensions or simple deionized water slurries. I and some of the users of these products are having particularly good results on linen belts, which are flatter than cowhide leather belts and have smoother joins and don't stretch, reporting excellent longevity and rapid cutting rates. Using coarser grits as coarse as 80 microns, they are using it after a 220 or even 120 grit belt for all remaining operations. The myth that compounds on strops cannot generate burr is pretty much exploded using powered applications.

Hope this gives a good overview of useful instances for deploying CBN on surfaces other than Kangaroo. As yet another topic, CBN works quite well on stone surfaces - both natural and synthetic to extend the range of use of these stones to more abrasion resistant steels. This is worth a whole separate discussion.


---
Ken
 
Are ken as in Ken Schwartz? Thanks for your replies. It's very informative and I think this thread has provided a lot of information to the knife nuts out there.
 
Yes, I'm Ken Schwartz :) Glad to provide information of use to this community. Please ask me questions here or contact me via PM's emails, etc. Always glad to talk about sharpening :)

Thank you for your kind words. Much appreciated.

---
Ken
 
Ken, might we examine the point on which we disagree?

While I don't contest the fact that the pounds per sq. inch differ significantly between a fingernail and a knife blade, in your post you say;
' Here thinness is a more significant advantage.' Is this to mean that because of the thinness of the split leather Kangaroo used for stropping, it gets enough support from the backing media? That a thicker piece of Kangaroo leather would be too soft to use for a flat bevel without extra diligence in blade pressure? If so, perhaps my fingernail test isn't so far wrong, despite the actual numbers. After all, the results are that if the thick leather is soft enough to indent easily, then as you say, one must use an extremely thin split on a hardened backing to make it work properly (for a flat bevel.) That, or a properly processed piece of nice thick cowhide or Shell Cordovan horsehide.


Stitchawl
 
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Stitch,

You're overthinking and confusing the issue. If you have 'something' that is compressible that is thin, there's less to compress. If it's thicker, the compression will be greater. If you have a wool sheet over a wooden board or a wool blanket over a wooden board and you lay a weight on both, which will stay flatter? If one strop of thin leather is a fraction over 1/8" thick and only 1/32" is the leather but most of that 1/8 " is a stiff backing like glass or Aluminum, there will be less give then if there is 1/8" or more of a piece that is all a compressible substance. The fingernail test is still not a useful test as it is measuring something that does not occur during stropping. If you were CUTTING both leathers, it might be of some relevance. You are extrapolating the data at very high pressures over a range of low stropping pressures to draw a false conclusion.

Kangaroo is a naturally much thinner leather than cow or horse. Much thinner. In fact, I pay a premium for 'select' Kangaroo that is thinner than average Kangaroo for this specific reason. If I wanted Kangaroo as thick as cow or horse, I would need to enlist the services of a genetics engineer to gene splice Kangaroo DNA with a Tyrannosaurus to get some giant Kangaroos :) I can't get Kangaroo as thick as horse or cow. It is the nature of the beast.

Now does this argument against Kangaroo have any practical validity? Well if I had problems getting flat bevels on Kangaroo, I'd certainly be concerned. If I had problems with the [superior IMHO] surface characteristics of Kangaroo, I'd also be concerned.

Here's an example of a Kangaroo stropped knife edge with 0.025 micron polycrystalline diamond done on an EdgePro. Looks pretty clean and flat to me.

1401228_639010156149385_251602996_o.jpg


As this discussion is a bit off topic of the main topic of the post, if you have further questions about Kangaroo, could you simply start another thread and let us return to the original topic regarding compounds. Much appreciated.

---
Ken
 
In the long and the short of it. Stitchawl you use different techniques to take leather that is unsuitable for use as a strop. And turn it into a much higher quality stropping substrate. If you use your fingernail test to check your progress as your treating the leather great. I think it would work fine just as a reference while your working the leather.

Ken skips all this by using Roo , which comes so thin that it doesnt need to be treated/cased/pressed. Its so thin it cant deform enough to convex an edge. Believe me i have tried (using pressures in excess of 20# to try and do so.) The reason i use Roo when i do is for the heavy burnishing effect it seems to produce. I dont have an explanation for why it burnishes so much more than other leathers ive used. Ken and I have looked at some of my micrographs and our going theory right now is that it has something to do with the stiction you get when your angles are perfect when.stropping with roo.

Theres no doubt that processing / preparing thicker lower quality leathers improves thier usefullness as a strop. Its just not something needed with the roo strops.
 
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