CBN Rods

[Cliff Stamp]

CBN is a completely other story - it will not blink or change even at thousands of degrees - not so diamond.

CBN has a boron oxide layer (B2O3) which is what protects it from oxidization similar to the chromium oxide layer on steel protects the iron from corrosion. However this boron oxide layer is soluble in water in high temperatures according to :

B2O3 + 3 H2O -> 2H3BO3

hence why CBN is fairly inert it can be hydrolyzed by high temperature reactions with water producing B2O3 an NH3. Hence why there is generally a concern using water based vs oil based lubricants for CBN.

Now is this a practical concern in hand grinding - I have seen no evidence any of these reactions take place in the mechanics of hand grinding. But neither for the diffusion based wear and thermal degrade of diamonds taking place at such conditions either.

[Cliff Stamp]

...is it clever not only to work with slow pace but also to use (also on the sharpmaker) some sprayed on water to the rods as intermediary/coolant?

In general it is also a good idea to use a lubricant in grinding to minimize friction. Plus you don't want to be breathing in grinding dust and a lubricant will also minimize the chance of the edge catching on irregular grits and other potentially damaging events.

[Brunzenstein48]

A German rep and seller of Spyderco equipment informed me that the CBN rods were developed to replace the diamond rods because these tended to loose particles / prone to fall off, if to much pressure was applied by the user.
The CBN rods are, as he explained, much more resistant to wearing of.

[Cliff Stamp]

.... the CBN rods were developed to replace the diamond rods because these tended to loose particles / prone to fall off, if to much pressure was applied by the user.
The CBN rods are, as he explained, much more resistant to wearing of.

There is nothing inherent to CBN which gives that property, it is the nature of the bond not the abrasive. If they wanted to make a diamond abrasive with almost no possibility of tear out then they could have used a brazed bond for example. The abrasive can also be coated to increase the bond strength.

[Brunzenstein48]

Besides that CBN is the bonding and abrasive material in itself, nothing to attach - so, if the chap lied to me and your right Cliff, what else could the reason spyderco sells two nearly identical items for about the same price?
They are no idiots. At least as far as commercial history shows.
Are CBN cheaper to produce?

[Cliff Stamp]

Besides that CBN is the bonding and abrasive material in itself, nothing to attach ...

In general with metal bonds there are multiple modes of fracture/pullout :

-the abrasives are often coated to make them have a stronger bond (50% greater bond strength)
-there is a bonding media which attaches to the abrasive
-there is a bond between the substrate and the bonding media

This means there are five modes of failure which can create tear out :

-a large piece of the abrasive can crack off
-the abrasive can come off the coating
-the abrasive can break away from the bond
-the bond can break itself (bond bridge failure)
-the bond can pull off / break free the substrate

This is why modeling abrasive life is not so easy as this is just fracture and you can see there are many different ways and they will have different effects on the abrasive.

- so, if the chap lied to me and your right Cliff

I don't think it is fair to call everyone who is mistaken a liar. He is a sales rep, they are given information and their job is to present it. Their job isn't to do R&D to determine how products behave. Plus, lets me frank, he is a sales rep, it really isn't a great idea to ask them and expect unbiased information. If it was true for example a company was just trying to liquidate a surplus would the sales rep actually tell people something like "look, we just have to get rid of this as it is costing us money" or would they try to find someway to promote it.

Here is the thing, I don't want you to believe me because I said something, that isn't how science works. I want you to actually go learn about metal bonding, don't ask sales reps, go read the actual literature, the research in tribological journals.

what else could the reason spyderco sells two nearly identical items for about the same price?

Lots of reasons, the fact there is that much discussion/interest is an obvious one. How much discussion was there over the diamond rods on the forum before the CBN rods were introduced, now look at the discussion. But here is the thing, I am not terribly interested in why Spyderco made them, that is a business/economic question and often ends up into conspiracies theories (they have to have a reason and thus ...) . I am only really interested in how they behave which is a physics/materials question.

Are CBN cheaper to produce?

Diamond is WAY less expensive, they are not even in the same class.

[Brunzenstein48]

good that I ordered the CBN rods instead of the DMT and that I marked my off-base brown middle rods accordingly.
Thanks for the explanation Cliff - good to have you around here. Sharpening and all stuff around that matter is a sience you don't get on campus (only parts of) but in life