CBN Rods

[defenestrate]

I've always used my forearms or thighs instead of fingers. Cut fingers are irritating to use, and as my primary active interface to the universe I try to minimize extra sensation like stinging small cuts. Inner forearm is fairly sensitive. Don't do this if you've had a few beers.

[Cliff Stamp]

Here is a sample of knives :



-green paring
-solingen
-wellington sword

-martha stewart
-levco
-blue paring knife

These are used in the kitchen by non-knife people, they can last weeks to months before sharpening depending on how often they cut on plates and such. I have tried very high end knives but it makes no difference, anything goes dull rapidly in those conditions and these blades are very durable (won't break) and very easy to restore. Note the awesome custom pine handle on one of them which is held on with gorilla glue.

They all have < 10 dps edge angles, and the edges are < 25 thou thick. They are reground to < 5 thou about once a year. They are maintained usually on either a fine DMT rod (only one step needed) or a benchstone + MXF DMT plate (I just cycle the sharpening to see if the finish makes a difference in edge holding).

This week I used them to compare the medium rods vs the CBN rods by separating them two groups at random. All knives were cut into a cheap benchstone twice to grind the edge to a flat and then bought to an apex on the flats of both rods. The results in terms of number of passes per side :

medium rods :

-green paring : 25 pps
-solingen : 150 pps
-wellington sword : 140 pps

CBN

-martha stewart : 20 pps
-levco : 20 pps
-blue paring knife : 12 pps

These knives have a random amount of damage when they are ready to be sharpened, but it is unlikely that the spread in the damage could explain that very large difference and it would be expected that the CBN rods cut much faster. The difference is readily just felt in the honing. Again :

-honing is done very light
-water is used (to control dust and act as a mild lubricant)

I will repeat this a few times and once the sample is > 20 knives it should be stable enough for a definite numerical comparison. However even with that brief data sample it kind of paints a fairly strong picture that these rods would be useful to augment the Sharpmaker for working on that kind of very heavy duty knives.

[Cliff Stamp]

As a curious aside, I have asked random people to try these out vs the medium rods in sharpening. With very few exceptions, most people who do not know much about sharpening, absolutely hate the CBN rods due to the noise and feel of the knives on the stones. The have an instinctive reaction that the rods are "destroying" the knives and they would never want to use them on their knives. In contrast they like the feel / sound of the brown stones and often make arguments that the extra time is needed to do quality work and that the CBN stones are "rushing" it and willing to damage the knives in the process.

[Blerv]

Interesting Cliff. I feel the same about the diamond stones which probably speaks to my inexperience with sharpening media more than anything :) . I had to reprofile a Dragonfly for my Dad and the diamonds worked well but I was thinking I would rather go slow and do my own knives on the brown equivalent. That or a similar bench stone.

Funny thing is I assume a large benchstone of a less aggressive grit (than diamonds or CBN) would cut FAR faster than a smaller, more aggressive crock stick based on surface area. Given enough speed, grit or both you can mess up anything I guess. "You" I mean "me", of course. :p

[Cliff Stamp]

Yes, with the rods you are not getting the full contact area even if you are very careful.

It is a matter of perspective and what you want. For me I often have friends drop off large groups of knives, often damaged and I have developed a method to apply a decent level of sharpness in a very minimal amount of time with minimal equipment. I was hesitant in the past to recommend the Sharpmaker to people because unless the edges matches well they would end up doing little to nothing and getting frustrated. However based on how fast the CBN rods restored the very damaged edges on those kitchen knives that isn't an issue.

However the problem then becomes the cost of the base kit + rods as it is out of the range of a lot of people. I would wonder could you actually make a rod which had three sides but one was CBN/400, one was the medium rod and one was the fine. Just make three flat plates and then join them together. While having three surfaces is nice sure, for someone who doesn't sharpen a lot and wanted a lower introductory cost then having a basically "triple stuff" rod could make it a lot more attractive to them.

[mattman]

Any speculation when these might hit the streets?

[Blerv]

However the problem then becomes the cost of the base kit + rods as it is out of the range of a lot of people. I would wonder could you actually make a rod which had three sides but one was CBN/400, one was the medium rod and one was the fine. Just make three flat plates and then join them together. While having three surfaces is nice sure, for someone who doesn't sharpen a lot and wanted a lower introductory cost then having a basically "triple stuff" rod could make it a lot more attractive to them.

The idea of a multi-grit 2x8 would be awesome. It would be really cool if Spyderco built a mount that would allow it to be placed at a 45/30 degree angle too.

Throwing out ideas. :)

[RealKnifeUser]

I definitely need these. Cost is of no concern, I'm going to get a pair. All the sharpmaker was missing is these, at least for me. Now can be used for my microbeveler, maintanence, and a perfect traveling sharpening kit.

[Cliff Stamp]

Here are the diamond rods :



The grit size looks very comparable to the CBN rods though if you compare the two picture size by size the diamond ones look to have more of the smaller particles. It will be interesting to compare them.

[RealKnifeUser]

Thanks for the testing and info Sal and Cliff.

[Donut]

They can do the double stuff medium/fine stones. Maybe you can do a split in half medium/fine triangle set and do one combo diamond/CBN triangle set and pray it ends up being the same price as the normal sharpmaker.

Do you really think people would be able to tell the difference between diamond and CBN? (Maybe that will be answered by your next report.)

[mattman]

Do you really think people would be able to tell the difference between diamond and CBN? (Maybe that will be answered by your next report.)

My guess is that this is a coarser grit than the diamonds...

The biggest complaint about the Sharpmaker is the time spent reprofileing... Many have made do with modifications such as leaning a XC DMT Aligner plate against the triangles, or purchasing the stones from Congress Tool (that are hit-or-miss on fitting the base), or wrapping the triangles with sandpaper... So a coarser grit seems the next logical step, to me, anyway.

IDK... Maybe it's just wishful thinking.

[bearfacedkiller]

I'm anxious to see if these are more aggressive than the diamond rods, I really hope so!!!

[Cliff Stamp]

Do you really think people would be able to tell the difference between diamond and CBN? (Maybe that will be answered by your next report.)

I will tell you this evening if I can. I just need to pick one knife to grind the edge off a half a dozen times and reset it with each of CBN and diamond rods.

I have an Elmax and S30V blade which have issues which I was intending to see would resolve if I ground more material off of them, I will likely use one of them.

[RealKnifeUser]

Is the S30V knife you speak of the Surefire?

[Cliff Stamp]

Yes, nice guess.

On Bladeforums one of the common complaints about experiments I did was that they always "worked out" and that they "agreed" with what I asserted. Now it is hard to discuss such things when such statements are made, it is like trying to discuss evolution with someone who states they believe the earth is hollow. Of course the experiments I describe "work out" because in general you don't publish the failed ones, and of course my experiments "agree" with what I assert because if they didn't I would change what I asserted as it is based in part upon the work I do.

However experiments don't always produce the results expected in which case you have to repeat them until consistency is obtained and you are sure that the unexpected results are right -or- you have to test out the hypothesis for why specifically the results are different. I will describe now an example of exactly this type of event. Here is the experiment :

-using a Surefire Delta with a zero grind
-cut the bevel off with 2 passes into a coarse benchstone
-apex it with the CBN rods

repeat the last two five times. The results as number of passes per side are :

CBN : 11, 11, 20, 17, 29, 26

Now this makes sense as you would expect as you keep apexing the bevel it gets wider and then takes more time to apex.

Now with the diamond :

-zero grind the Delta on a Bester 700
-cut the bevel off with 2 passes into a coarse benchstone
-apex it with the diamond rods

What would you expect as the results, I bet it isn't this :

Diamond : 3, 7, 10, 14, 20, 31

The diamond rods apex the bevel much faster initially, and so it would appear that the diamond rods are in fact more aggressive. However I don't think this is the case because at the end note the pps numbers almost equalize. I think that the reason for this is that the second time I flattened the Surefire I took out a small curvature near the edge and thus the diamond rods had less work to do initially.

This seems to be indicated by the pictures of the microbevels :

CBN :



Diamond :



Note how the diamond one is much more narrow initially.

Now if my hypothesis is correct then when I flatten the Surefire and repeat this that dramatic early difference will disappear. If it doesn't then that would be kind of interesting, but I don't think that will happen.

Normally I don't describe the experiments until they are finalized, repeated and everything is consistent, but I thought it might be of interest to describe what happens in some cases and why it is so important to repeat things a few times and try to make sure that what you think is causing what you see happening really is what is causing it.

[Bill1170]

Cliff,

Here is another factor to consider in comparing diamond and CBN rods. I don't think you've spoken to this, yet, for these rods. We know that diamond stones break in with use, assuming a less aggressive grit than when new. CBN may do the same. The question in my mind is, does this process proceed at different rates for the two materials? If so, then aged performance comparisons between the two may diverge from comparisons when new.

Thanks for doing these experiments and evaluations. I don't own the diamond rods, and am considering buying the CBN rods, pending feedback.

Bill

[Donut]

My guess is that this is a coarser grit than the diamonds...

I think that the diamond and CBN rods are similar grit.

[mattman]

I think that the diamond and CBN rods are similar grit.

I was doing a little casual browsing last night, trying to find the grit/mesh value of the diamond roos, and it seems they are also at 400 (approx)...

I was thinking they were 600...

Now I am curious if these are meant to replace the diamonds...?

[phillipsted]

Any indications of when the CBN rods will be available for purchase?

TedP