CBN Rods

[Cliff Stamp]

As an update, as an experiment I am likely not going to do again :




1000 cuts through used screw ties with a custom O1/61 HRC (tripled tempered) slipjoint, the edge angle was 15 to 20 dps (difficult to measure because the edge was 0.002-0.003" thick).

This only blunted one section of edge which was likely dirt as it happened in the first 25 cuts and then the next 975 did nothing. This is the damage in that section :





Note the small edge fold.


Edge was reset on the CBN rods on the sharpmaker to 15 dps :


-125 passes




I then micro-beveled it with the fine rods / 20 dps :





The fine rods can micro bevel the CBN rods instantly as in five passes per side, however you can still see some of the aggressive teeth of the CBN rods so you get a mix of high push cutting ability (catches hair above the skin) and still decent slicing ability.

[sir_mike]

How do these fit into the lineup of the rods? Are they to replace the diamond ones and are they more or less coarse than then diamond ones. Any one try these yet? If so, comments?

Thx.

[Tabo]

I began another thread on here about my Spyderco Dice not having a very good edge when I received it new, so I invested in some CBN rods since I only have the Sharpmaker to sharpen my blades. I received my CBN Rods yesterday but didn't get a chance to re-profile my Spyderco Dice (CTS-XHP) until today. Let me tell you, they worked out perfectly!

I started out on the 30° side of the Sharpmaker and ran 300 passes on each side of the blade using the triangle sides of the CBN rods. Then I ran 20 passes on each side with the flats of the rods. I finished with 30 passes on each side with both the medium and fine rods using both the triangle and flats of the rods.

At this point the blade could cut paper but still wasn't hair popping sharp.

I moved to the 40° side of the Sharpmaker and ran 20 passes on each side of the blade using the triangle sides of the CBN rods. Then I ran 10 passes on each side with the flats of the rods. I finished with 30 passes on each side with both the medium and fine rods using both the triangle and flats of the rods.

After doing this it was shaving arm hair like no other and slicing paper like a laser!

So for anybody on the fence about the CBN rods, I cannot recommend them enough!

(If anybody wants to know, I used glass cleaner on the CBN rods after 20 passes on each side to keep them clean and lubricated.)

[Cliff Stamp]

Are they to replace the diamond ones and are they more or less coarse than then diamond ones.

They are similar in finish/coarseness to the diamonds, details in previous posts above.

[nccole]

They are similar in finish/coarseness to the diamonds, details in previous posts above.

I am thinking one or the other is necessary and not both. With your extended time with each now, which would you recommend to add to the standard system (with UF rods too)? Price is the same where I have seen them, so I am unsure which to get.

[Jax]

Good stuff Tabo! Thanks for sharing your insight's!
Thanks also to Sal and Cliff for making this thread possible :)

[Mjc1973]

So Cliff, knowing what you know now and if you needed a reprofile an edge (I do. I screwed up my first spyderco knife by using the work sharp ) which of these 2 would you choose?

[Cliff Stamp]

In regards to one or the other :

-they have similar cutting speed and finish

from the half a dozen regrinds I have done with them. The interesting part is durability which takes a LOT of work to do. I actually marked the sides on them and am just using one side and after some work I am going to check them for relative wear, but that will take a LONG time to notice a difference with sensible use.

Another question would be durability in adverse conditions :

-no lubricant
-lots of force

and see which one just breaks faster.

[Mjc1973]

It sounds like maybe for me who is someone who will not probably do massive amounts of regrinds that either will serve my purposes equally well and I am not losing anything with whatever choice I make.

Would you agree?

[Cliff Stamp]

Update, comparing the Sharpmaker/CBN rods at 15 dps vs the WE 100 grit diamond at 15 dps :



Sharpmaker/CBN used on the knives on the right, the number of passes to apex the bevel :

-Bread : 10
-Solingen slicer : 70
-Chef : 90
-Paring : 15

These knives were all very dull, had little ability to cut even thick paper, could not open plastic packages, would crush a tomato. The edges were all visible, major areas of impact/nicks.

The CBN rods with just 10 passes per side had the edges cutting paper for 90%, the rest of the passes were mainly cleaning up the last inch or so of the tip as that always gets the most beating on plates and such.

In any case you can see that with very little time even seriously dull/damaged edges can be brought back to fine cutting. To finish, just switch to the 20 dps slot and give a few passes on the medium or fine (or both) as desired.

--

On the left with the WE/100 diamond :

-Bread : 50
-Levco utility : 150
-MS Chef : 100
-Paring : 300

Now before any judgment is made on the relative cutting speed, these knives could have been slightly more dull (it was a random selection) and the stroke length on the WE is only about half of that on the Sharpmaker so you need to cut that in half to have a similar length comparison (abrasive to abrasive) if you do that then you get :

Sharpmaker : 185 pps total
WE : 300 pps total

However the main difference was on the paring knife which was extremely impacted, I believe it was used to scrape down a grill. As with most comparisons which are random in nature you would need to do a lot of them to see if any difference was significant. But a few comments from people I had doing the work :

-the Sharpmaker is much simpler to set up use
-the WE looks more "professional", but can be a bit confusing about how to to put together and use (angles, grits, etc.)
-the WE seems dangerous (upturned sharpened blade)


A few limitations :

-the Sharpmaker easily handles the extreme curve on that black paring knife (with the corners)
-the WE can not sharpen the heel of those narrow blades on the 15 dps setting (you grind into the blade clamp)
-it is trivial to wedge the Sharpmaker to grind at 10 dps if you want, not so with the WE
-it is easier to focus on spots with the WE

[Cliff Stamp]

Here is a not so obvious use for the rods :



+



Machetes often get a bit dinged up because of rock and other hard contacts, hence is is nice to have a decent file when you are doing serious work. After you have filed the edge back into shape you will have divots left in the edge. It is a waste to actually try to grind them out fully, the machete would be reduced to a fillet blade in short order.

However the corner of the CBN rods can easily work in the divots left and turn them into sharpened serrations. This really isn't done to give you a serrated blade as much as it is to make them sharp as if they are dull it just increases the risk of further damage in those areas.

[connor]

Got my pair of CBN rods today. Unfortunately one of the rods is slightly "twisted" along the longitudinal axis so that the flats are not plane anymore - only noticed this after I put them into the Sharpmaker base to start sharpening.
If you look along the rod the twist is clearly visible, though. Gonna have to send it back. :-(

EDIT: Added a picture. Note the top right corner.

[Cliff Stamp]

I carry one of the rods and use it to sharpen a lot of utility knives, it isn't the ideal finish for it as it is really coarse however most of the blades are very dull, often damaged so it quickly gets it sharp. I have been asking for feedback and most of it has been really positive but again they are comparing the sharpened blade to a dull one so that doesn't really say much aside from very sharp blades (of any finish) cut better than dull ones.

I got a big bunch of the same cardboard boxes this weekend and decided to do a direct comparison in a simplified data collection/analysis. I have been refining my methods to speed them up but still get decent information :

-1/8" corrugated card stock, cut across the ridges in 30 cm slices
-sharpness tested by slicing bergia spinning thread under a 50 gram load

This was the blade :



It is a very common utility style blade, this is a folding model of the common Stanley. I compared :

-the as-boxed sharpness and edge retention
-the sharpness and edge retention off of the CBN rods at 15 dps

The sharpening was :

-10 pps, light force
-5 pps, very light force (5-10 grams)
-2 pps on the 20 dps side, just barely touching the stones

The CBN rods can easily produce a shaving edge using that method.

I did four runs, a quick check just to see what kind of difference was produced. The initial sharpness (lower number is higher sharpness, it is linear) :

As boxed : 23 (4)

CBN : 18 (2)

No significant difference, this was kind of interesting. I wasn't expecting to produce an edge which may in fact be sharper and is more consistent with the CBN rods.

In regards to edge retention I calculated the lifetime cutting efficiency which is basically the amount of material cut for amount of work you do cutting. The results (higher number is better edge retention) :


As boxed : 40 (3)

CBN : 30 (3)

The CBN edge retention while lower isn't significantly lower (the random spread in the results is large enough to prevent rejecting the null hypothesis that the edge retention is the same).

In short :

-the initial sharpness and edge retention are not significantly different

Now I only did four runs and cardboard is very variable in cutting - but still this is far more controlled than what anyone would see in actual use. This means that that initial sharpness and edge retention in use are likely to be seen as the same. This is kind of interesting when you consider the CBN rods very quickly reset the edge on these utility blades, even just 5-10 pps will get the edge back to cutting very well even when significantly damaged because the rods are so coarse.

After using these for awhile and sharpening many utility knives their usefulness outside the Sharpmaker is proving to be very high, so much so most people will ask "Hey, you got that file?" because of how simple it is to get an edge back shaving and cutting well.

--

Now to clarify something, I am comparing the edges in slicing which is the most favorable way for CBN, if I was push cutting plastics then the results would be expected to be different. I will likely do this later as well as maybe add a couple of more cardboard runs to see if I can see if they will be different if I refine the results a little.

[Cliff Stamp]

I found some more cardboard of the same type and did another couple of runs :


As-Boxed :


-IS : 20.8 (2.9)
-TCE : 38.3 (2.5)


CBN :


-IS : 19.0 (1.8)
-TCE : 30.4 (2.1)


No significant difference in the initial sharpness and while I would bet that if I ran more data the edge retention/efficiency would be lower, the random variation is still too large to say that with confidence.

In short, this semi-controlled run of 10 cutting trials shows it would be very unlikely that someone would see a difference slicing cardboard with the two finishes in regards to ease of cutting or lifetime. Given at how fast the CBN sharpens those blades that is a fairly useful tool indeed to have on hand.

[Mike157]

Thank you for the updates Cliff. They are always valued and appreciated along with the your demonstrated practical applications (working the machete edge). I have a folding box cutter that I use frequently. Can't wait to give the CBN rods a try with it. Mike

[Cliff Stamp]

I have a folding box cutter that I use frequently. Can't wait to give the CBN rods a try with it. Mike

Let me know how it works out. I think a final bevel with the medium rods would be better for this work, however this is more of a practical demonstration of what people with those blades would actually use. They are simply not going to carry multiple rods and go through a grit system. They are going to want one rod which can easily restore even a damaged edge and get the blade cutting fast. I didn't expect the CBN to exceed the as-boxed edge but was surprised by how well it did as were all the guys who I used it on who all think "its a **** of a file" .

[Cliff Stamp]

I normally only post the results of finished work, as a point of reference when the work is in progress it isn't always stable and thus you can appear to see effects which could be nothing more than random deviations. For example :






The as-boxed is the baseline, all of these I can explain and are understood but I am not that confident in the last two results. I think the order/ranking is correct but the magnitude I do not have much confidence in because they are only based on three runs each and cardboard is so random even if it all comes from the same source as it was here.

What I think is happening is that the medium rod alone finish is deforming/placing the edge under strain and thus even though it is sharp it collapses readily in use. The edge once reset on the Bester and then finished on the medium rods has the optimal edge performance for individual hand sharpened blades. I would expect that to be higher but I think the amount will come down if I can find enough cardboard to double the runs.

Note all sharpened edges are at 15 dps with a 20 dps deburring and then back sharpening at 15 dps.

[Mike157]

Hi Cliff,

Could you clarify (for my simple mind) what you mean by the medium rod only edge finish may be "deforming/placing the edge under strain"? Are you saying that at the angle the brown rods were used, the angle may have been too low and not enough material was left behind the edge to support it? But then that would mean the Bester reprofile was actually creating a larger angle? Or are you saying the brown rods were just mushing, so to speak, a new edge into place and that process does not make for a good edge. Almost like creating a burr to create an edge out of it? Or am I totally out of the ball park?

I'd like to understand this not only just to understand it but it seems this situation would be applicable to other sharpening situations. Thank you. Mike

[Cliff Stamp]

Hi Cliff,

Or are you saying the brown rods were just mushing, so to speak, a new edge into place and that process does not make for a good edge. Almost like creating a burr to create an edge out of it? Or am I totally out of the ball park?

Exactly right.

After the cutting which was about 500', the edges have actually very little wear, the blunting is mainly deformation as the edge is just pushed out of line. Always keep in mind steel, even the most basic steels is very hard and wear resistant compared to most materials. Just take a piece of cardboard and start rubbing it against a knife and try to wear a hole in the side, it is going to take a LONG time for the cardboard to actually abrade the steel.

If you use the rods then what happens immediately as in the first pass is that the edge is just pushed back into alignment. Therefore if you stop after just one pass per side the edge will be almost back to full sharpness, this is one of the reasons why people tend to like strops because just a few passes and the edge is sharp.

However there is a downside.

...it seems this situation would be applicable to other sharpening situations.

Yes, the edge retention and durability is lower, much lower. How much lower depends on how deformed the edge was before you started. This is the reason why I recommend always cutting the edge off before sharpening, using a decently coarse stone which can form the edge in about 50 passes per side or less and then finishing the apex.

A lot of people have the viewpoint to do the minimal work in sharpening with the perspective to "conserve" the knife but the reality is that what you are conserving is very low performance in regards to edge retention/durability. If you are going to do that then just buy a cheap knife as you can keep it sharper for longer with more aggressive sharpening.

Just think of all the work that goes into making a modern high performance steel and then think about putting that in a highly deformed/damage state and then using it. If it was done where you could see it you would immediately know it was wrong, but because people can't see it on the edge they do it.

People who are of the view "never let a knife get dull and you never have to spend much time sharpening it" tend to always work very damaged/strained edges because they are apparently terrified of actually sharpening them. This is one of the main reasons why most people have very low standards of performance as they think knives should actually behave as theirs do, but properly sharpened ones don't.

A properly sharpened knife should not just be sharp after cutting one 2x4, you should be able to chop through a hundred and still readily slice papers and fine grasses. You should be able to cut cardboard for a very long time, until you get bored and the knife will still be extremely sharp. Zip-ties and other plastics can be cut hundreds of time with no effect.

All of this is possible with simple and basic steels, if you can't do it then the knife simply isn't sharpened properly.

[Cliff Stamp]

As a note on use, I actually number the faces of the rods and the corners. The reason I do this is because the CBN rods are a plate coating and they will wear and become less aggressive. If you know this then you can take advantage of it and give yourself a multi-grit stone. For example right now I do all of the work on face #1 and on corner #1. When I notice that these have started to lose aggression as they have worn significantly then I switch to face and corner #2. I then use the first face which gives a finer finish after the face/corner #2 which allows a refinement of the scratch pattern and is especially critical when you are trying to set the apex (sharpness). In time the process will repeat and I will move to face/corner #3. At this point I then have a (pseudo) coarse, medium and fine grit CBN rods.