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Thread: CBN Rods

  1. #61
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    Quote Originally Posted by Bill1170 View Post
    We know that diamond stones break in with use, assuming a less aggressive grit than when new. CBN may do the same.
    I meant to discuss this in the video on the CBN, in some detail, (if you are not interested in the why just skip to the bottom -- part ):

    All abrasives, in fact all edges, or anything that wears tends to wear (or blunt, deform, etc.) at a rate which is inversely proportional to the extent of wear, that means that the more wear it has taken, the more the rate of wear decreases. It is easy to understand this if you take a sharp edge piece of wood and consider the edge thickness which is likely so small you have a hard time seeing it, some small fraction of a mm for a sharp square corner. Now take a sheet of sandpaper and rub it along the edge and you will find the edge makes a dramatic increase in thickness. Rub the sandpaper again and you will see the thickness increase but not as dramatic. Of course as the edge gets thicker you have to remove more material to make it thicken further and thus while initially one pass can easily double (or triple) the thickness, one pass at the 50'th point might make such a small percentage change that you can not even see it.

    If you do the math this means you end up with a general solution which looks like : W(x)=a xb+c. Here :

    W(x) is the wear at a number of passes (x)
    a,b,c are physical constants (depend on the materials, manner of work, etc.)

    Now the grinding ability (G) is just the inverse of this and that equation is :

    G(x)=G_0/(1+a xb)

    Here I have replaced c with G_0 for the initial boundary condition that at x=0 the grinding rate is just the initial (or as-boxed) grinding ability G_0.

    Now if you plot this curve in general you get something which looks like :



    This curve is comparing two blades for edge retention, but for the purposes here just look at the red/yellow lines/points and see how they decrease very rapidly initially but then tail off, that is what that curve looks like in general and it holds well for all general wear-type relations no matter the material.

    --

    In short, all abrasives will wear rapidly at first and then settle into a long plateau region where their rate of wear is so slow they basically stay there effectively forever under normal use. I have a diamond stone which has been used for ~20 years and is the same stone that I do all the 600 grit comparisons with and does a lot of my finish sharpening for general utility. I take micrographs of the edges it produces ever few years and they are not significantly difference under 50X magnification.

    The reason why people state this for diamonds and not for say water stones is that for waterstones as the grit wears they also break away from the bond and new ones are released, and they also fracture and produce new cutting edges. This allows the surface to maintain a consistent cutting pattern because the worn grits are simply replaced. However if you have ever used a grinding wheel with an extremely dense/tight bond you can see it smooth out and have to be resurfaced as the grits are wearing down and the bond holds them so tight that new ones are not released.

    Now what I would recommend is different than what a lot of people say about using plated abrasives which is use them first on some cheap knives. I would not recommend that because often it makes people intentionally try to "break them in" by pushing too hard/fast and this will tear out the abrasive or break it apart. What I would recommend is :

    -use water

    This has many benefits :

    -acts as a lubricant which will allow the edge to skip over any really rough patches
    -catches the dust (keeping it out of the air and your lungs)

    and second :

    -go light

    I mean light here as in the least force you can apply. These abrasives (diamond/cbn) are extremely hard and very sharp, to them steel is very soft, it is like comparing steel to butter. They will cut it with extremely low force, especially when new when all of these edges are very sharp. If you want to cut faster just use a more coarse grit, but always keep the force very low. As the abrasive wears then you can slowly increase force, the goal is to keep the feel the same.

    Essentially this is called finding the sweet spot in grinding, the amount of force you have to apply to get the grits to cut at a depth which gets the grits to cut deep enough so there isn't any skipping, but not so deep they get torn out, they just wear slow. With diamond and cbn, I have found that initially, this force (especially on narrow stones) is really light.

  2. #62
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    Again here :



    Note that I am using so little force that it is at the limit of just keeping the edge on the rods.

    (In this video I was not using water as I was trying to capture the abrasive and see if I could tell anything from the magnified view. I was curious if the filings produced looked any different from the CBN rods vs a coarse stone for example. I could not see any difference at 50X magnification. )

  3. #63
    Spyderco Forum Registered User Blerv's Avatar
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    Thanks Cliff. Great stuff !
    Blake

  4. #64
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    Thanks, Cliff. I know about tearing diamonds off a nickel matrix, did just that to my XC Diafold when reprofiling some very blunt kitchen knives. I was impatient, pushed too hard, and killed the sharpener. Lesson learned. Let the tool do the work.

    As for water, I always prefer to use my diamond bench stones wet. They just feel better that way.

  5. #65
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    Quote Originally Posted by Bill1170 View Post
    Thanks, Cliff. I know about tearing diamonds off a nickel matrix, did just that to my XC Diafold when reprofiling some very blunt kitchen knives. I was impatient, pushed too hard, and killed the sharpener. Lesson learned. Let the tool do the work.

    As for water, I always prefer to use my diamond bench stones wet. They just feel better that way.

    I repeated the CBN cutting and the numbers were more comparable to the Diamond :

    CBN R2 : 3, 7, 10, 14, 18, 22

    again these are the numbers of passes per side to apex the Surefire Delta (S30V) after grinding the edge off on a coarse stone and then apexing and then repeating for a total of six times. The passes steadily increase as the bevel gets wider each time :



    In summary :

    CBN---- R1 : 11, 11, 20, 17, 29, 26
    CBN---- R2 : 03, 07, 10, 14, 18, 22

    Diamond R1 : 03, 07, 10, 14, 20, 31

    Again, the reason I believe the CBN first round was higher initially was because the edge on the Surefire had a light convex bevel which was removed in subsequent sharpenings.

    At first pass therefore, again with very sparce data, it appears that they have comparable grinding speed and finish.

  6. #66
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    Update :



    These are a set of knives from Paderno, a few observations :

    -full height flat grinds
    -edges are <0.005" but not consistent (bevel can often double along the edge)
    -not dishwasher safe (will rust readily)
    -edges tend to chip more so than deform
    -all tips were broken off to some extent, little plastic deformation

    In short :

    -decent ergonomics
    -high cutting ability
    -low to moderate corrosion resistance
    -edge durability, low to moderate (no rippling of the primary)

    It is likely they were under soaked, and the steel was not well normalized and the quench was not extended. These are expensive, but you are paying for the brand name.

    However of interest here was the sharpening :

    Slicing/Carving knife :

    -edge bevel is between 15 and 20 dps, uneven
    -cut the edge off with two passes into a cheap stone
    -225 pps on the CBN rods, reset the bevel to 15 dps
    -10 pps on the medium, edge was cleanly finished to the medium grit

    Chef knife :

    -edge bevel is between 15 and 20 dps
    -cut the edge off with two passes into a cheap stone
    -less than 25 pp, edge was apexed at 20 dps
    -45 pps on the medium rods, including a deburring step, edge was finished on the medium rods

    In short :

    -readily capable of bringing very worn edges to an apex


    -easily takes down and edge and resets bevels on high grindability steels

    -micro-bevel are immediate to form from 15 to 20 dps

    -even a full polish on the 15 or 20 dps bevel only takes a few minutes jumping from the CBN to medium (on high grindability steels)

  7. #67
    Spyderco Forum Registered User Donut's Avatar
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    So, you think diamond is similar performing to the CBN.

    Would there be any advantage to CBN, like your special mule?
    -Brian
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  8. #68
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    Quote Originally Posted by Donut View Post
    So, you think diamond is similar performing to the CBN.
    It appears to be, however here are some questions :

    -what happens if you work on extremely high alloy steels (121 REX)
    -what about ceramics
    -is one more durable/fragile when used abusively
    -is the lifetime similar

  9. #69
    Spyderco Forum Registered User phillipsted's Avatar
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    Thanks for the update, Cliff. Very interesting.

    Any word when these will be commercially available?

    TedP

  10. #70
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    Should be soon now.

    sal

  11. #71
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    Hi Sal! Are these meant to be a replacement for the diamond rods, or available in addition?

  12. #72
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    At this time, they're an addition.

    sal

  13. #73
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    As an update, the following kitchen knives were sharpened :

    -Wellington Sword : chef, bread
    -Japanese : bread
    -Levco : butcher
    -Solingen : slicing/carving
    -Martha Stewart : Chef
    -No name : paring

    These are all used by non knife people which means they cut bones, cut on plates, counter tops, scrape pans, etc. . They are usually sharpened weeks to months depending on how much use each gets.

    I apexed the edge with the 15 dps setting on the sharpmaker, at this point they are easily sharp enough to slice very fine papers and sharper than most knives in kitchens. I finish the edge with a mxf DMT, but the medium Sharpmaker rods would do well for most also.

    CBN :

    -Wellington Sword : chef, 25 pps
    -Wellington Sword : bread, 10 pps
    -Solingen : slicing/carving, 20 pps

    Very light force is used, just enough to make contact, the stones are very aggressive. Again, these edges have visible dents, rolls and chips, you can clearly see light reflecting from them and they will not even slice stiff paper, but after just a couple of dozen passes the edge is cleanly apexed and slices fine papers.

    Diamond :

    -Japanese : bread, 10 pss
    -Levco : butcher, 80 pps
    -Martha Stewart : Chef , 30 pps
    -No name : paring, 100 pps

    Similar results, the Levco and paring were extremely blunted, the entire edge was compacted flat, however the rate of sharpening was rapid and every ten passes the light reflecting from the edge was clearly reduced. The last 50 pps were cleaning up the tips which had been heavily used as scrapers.

    For non-knife people, one of the issues of the Sharpmaker is that those people tend to be very hard on their knives which usually have visible damage then they need to be sharpened, the medium rods are quite fine (in general as an abrasive) and thus take a lot of time to handle those knives.

    However the CBN (and diamond) rods will easily handle edges which are far beyond the type of damage that most people here will put on their knives. In addition to allowing angle changes (which is what the forum members are likely to appreciate). They would serve as a general sharpening tool for people who use there knives much harder.

  14. #74
    Spyderco Forum Registered User jabba359's Avatar
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    Quote Originally Posted by Cliff Stamp View Post
    It appears to be, however here are some questions :

    -what happens if you work on extremely high alloy steels (121 REX)
    -what about ceramics
    -is one more durable/fragile when used abusively
    -is the lifetime similar
    With the performance similar to diamond, I'm interested in the last two questions (I don't plan on sharpening ceramic blades or anything like REX 121). I don't have the diamond stones for my Sharpmaker, but would like to pick something a bit more aggresive up that will help me reprofile quicker. So for me, probably the single biggest factor would be the lifetime to cost ratio. Thanks for testing these out and sharing your findings.
    -Kyle


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  15. #75
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    As an update :



    This is a knife used to cut batt-insulation, it is heavily worn :

    -points are rounded off flat
    -the first section of the blade (about half an inch is ground down to a 1/16" flat from cutting on cardboard)
    -inside the scallops are chipped/dented

    The latter damage comes mainly from cutting other things on site, wires and such most likely.

    These are just thrown out, however using the corners of the CBN rod on the scallops and the flat on the back in just 25 passes the knife easily slices magazine paper.

    The CBN rods some in plastic tubes with end caps so it is trivial to pop one in your pocket, keep it in your glove compartment, etc. . It is aggressive enough to do very quick field repairs and get blades back to cutting.

  16. #76
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    Thank you for the continued updates Cliff. They are appreciated. Your practical, real world data not only encourages me to give applications similar to what you describe a try, but also gives me an indication of the results I can achieve. Thank you. Mike

  17. #77
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    Mike, the rods are pretty versatile, if you had one with a tri-surface (CBN, medium / fine ceramic), it would be a pretty cool little sharpener to carry around in the tubes they come in.

    --

    Checking the CBN on some fairly hard / high carbide steel, I used it to reset the edge on a OTK EDC in k390 / 64 HRC (bottom knife, the top knife is from ESEE) :





    Used in the kitchen the edge retention was moderate likely because of corrosion as it as it also spotted with orange scale readily right through the forced patina.

    --

    On the right side, a quick 25 ps showed that side was < 15 dps as a micro-bevel formed. That is a decent sign as the edge bevel will be taken down to 10 dps after it has been used at 15 dps for awhile if no significant problems happen (none are expected). No further work was done on that side as this was just mainly a shaping exercise.

    On the left side, another quick 25 ds showed the edge cleanly being ground to the apex near the choil, but it was just grinding the shoulder through the second half of the blade. After 150 ps (total), the edge was cleanly apexed on the left side except for a cm of edge which had a strong micro-bevel. It took another 200 ps to minimize this to a few mm in length and complete the apexing in the tip.

    In short the CBN rods cleaned up an edge which had multiple bevels from < 15 dps to > 20 dps in sections on a fairly hard and high carbide steel in 400 passes, that is just a few minutes work. The edge can now easily be sharpened with the 20 dps setting if desired.

    --


    I attempted to measure the force I am using, however it is very light, it won't even move a bathroom scale so it is << 1 lbs as expected. I will check it on a food scale later.

  18. #78
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    I'm looking forward to trying these out, I have a pair of the CBN rods on the way!
    Which Knife, A or B? get Both! (and C, D and E)

  19. #79
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    The pair I ordered arrived recently. Will give them a try shortly. Thanks again Cliff. Such great applicable information. Mike

  20. #80
    Spyderco Forum Registered User AKWolf's Avatar
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    I Just ordered a set from KC . The marketing material on the rods, suggests using less than 5 grams of pressure when re-profiling .
    9 er's.....

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