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Thread: Edge Retention (cardboard) : Sharpmaker medium rods - 15 vs 20 dps microbevel

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    Edge Retention (cardboard) : Sharpmaker medium rods - 15 vs 20 dps microbevel

    If a knife is sharpened with 15 vs 20 dps micro-bevels which one has increased edge retention and why :



    Note the results of that experiment do not hold across all types of cutting or even all steels, but there are valid and interesting points which result from the comparison.

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    Spyderco Forum Registered User Evil D's Avatar
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    Geez Cliff, where do you live that it's already snowing?

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    Ha, it has been snowing for awhile. I would not expect anything heavy until mid to late Jan though.

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    Spyderco Forum Registered User 3rdGenRigger's Avatar
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    Quote Originally Posted by Evil D View Post
    Geez Cliff, where do you live that it's already snowing?
    Heh...you need lots of horsepower to drift down where it barely snows. I love the snow...all you need is a pickup, with a properly tuned engine, properly programmed transmission (If automatic), locking rear differential, and no weight in the box whatsoever. You go everywhere sideways in slow motion and it's epically good fun if you're a keen driver.
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    David,

    IIRC, Cliff lives in Newfoundland.

    Cliff,

    I'm going to surmise that the 15 dps sections were higher in initial sharpness and lasted better in the cardboard test than the 20 dps sections. Those knives you show look like the sort of cutlery made from low carbide content stainless, which if true, should exhibit good edge stability at the lower included angle. Looking forward to reading your findings.

    Bill

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    The results : http://www.cliffstamp.com/knives/rev...periments.html .

    In short :

    -15 dps is strong enough to prevent rolling/denting even on a true micro-bevel on a low main edge angle
    -a higher angle simply increases the rate of blunting at a given wear

    as a result the performance just degrades as the angle is increased from 15 to 20 dps.

    Now there are many interesting things which come out of this result, one of the main ones is that lower carbide steels which are stable at lower edge angles not only have higher cutting ability as they can take finer grinds, they even have higher edge retention due to the ability to be stable at lower micro-bevels.

    In addition they also have higher grindability, machinability (low cost, much higher fracture toughness, etc. )

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    Spyderco Forum Registered User dbcad's Avatar
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    Hello Cliff, Over time more and more of your perceptions are being recognized and understood by a thick person like me I'm an avid follower of your posts and thank you for the time and effort you sacrifice to educate Science, experience and knowledge are very good things

    The old ~1060 knife will get a nice low edge angle
    Charlie

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    Spyderco Forum Registered User Brock O Lee's Avatar
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    Thanks Cliff, that is very interesting.

    An ave 66% increase in edge retention between 15 vs 20 deg is quite dramatic.

    If you had to make an informed guess, what would be the low range on the micro bevel angle for high carbide steels like S30V / S90V for light duty every day carry use?

    I keep mine at 15 deg and they seem to hold up well enough for my typical light usage.
    Hans

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    Spyderco Forum Registered User _centurio_'s Avatar
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    Thanks a lot Cliff! Your work is very complex and interesting. A lot of work isn't it?

    Rock on Cliff!!!

    @Brock:

    http://www.cliffstamp.com/knives/reviews/cardboard.html

    For example you cut a lot of cardboard. Due to cliff the tested knives made of S110V, S125V and Cpm 10V, have to many/large carbides for a 30 cutting edge (too less matrix to hold carbides stable).

    Oliver

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    Spyderco Forum Registered User chuck_roxas45's Avatar
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    I'm quoting this post by hardheart at BF.

    " Edge stability is not relevant with the sharpening protocol used. Edge finish is not the issue, primary grind is a contributor, but not the largest, sharpening angle is. There is too much matrix building too quickly behind the edge for the large carbides to be upset by cutting force to the point of detriment. The matrix is the matrix, if there is sufficient carbon after carbide formation, then there will be hard martensite in the carbide-rich steel just like the steel with no primary carbide. Martensite wears like martensite wears, so the difference is if there is anything else to help with the abrasive cutting while the martensite wears. If the carbides fall/tear out, then there is still jagged martensite that formed the boss around which the carbide lay. So, still a rough cutting edge, which will still wear, and will then present more carbide.

    Still waiting on SEM, it is taking a really long time to get all the results, but the initial results are what drive my comments. Reduce the angle and cutting improves. That is with a carbide-rich stainless that is nowhere near the toughness of 3V. Sharpening on a grinder with a 100 grit belt at 10 degrees per side gave the best edge life results. Not the worst, not sorta similar to a 3 micron abrasive, not marginally better. A massive improvement, despite the measurable truths of carbide size or temper loss from power sharpening. Knife edges are not thin, not even as you approach single digit per side angles. You can still whittle wood or maybe chop lightly. You will genuinely ripple the edge of a shaving razor if you cut mercerized thread. I've done it, it triples the force needed to make a cut after the first attempt, the edge is that damaged and visible under mild magnification. This is not comparable to even light knife use, and this is where edge stability is the most relevant. Add much more meat behind the edge, and carbides pretty much always help. Carbides and more steel don't help to shave your face, but that is what specialization in cutting tools is for."
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    Chuck, I'm lost at Hardheart quote ... Can share original thread?

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    I always heard that you catch more flies with honey than with vinegar, but then you catch even more flies with poop



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    Quote Originally Posted by Brock O Lee View Post
    An ave 66% increase in edge retention between 15 vs 20 deg is quite dramatic.
    This can be calculated, from the following two statements :

    a) the rate of edge thickening under a given wear is increased as the angle increases

    b) the increased edge angle increases the force around the edge (which also increases the direct rate of wear)

    Now to be specific the relations are on the tangent of the angle as these relate the thickness to the height at a given angle. This means that you would expect the following dependencies

    a) tan(angle)

    b) tan(angle)^(<1)

    Now for the second part the power is less than 1 as the angle is just a micro-bevel and thus the force would not be expected to be linear. In order to calculate it you have to calculate the integral of the force over the height of the bevel. However in general as a starting approximation roots are often a decent first start. This means that you would predict the performance advantage would be :

    [tan (20) / tan (15)]^1.5

    which predicts an advantage of 58% .

    However I have ignored another factor which is the resistance of the larger angle to fracture and deformation. Based on the images and performance I assumed that there is no deformation/fracture in the 15 dps bevel and thus 20 had no effect but this isn't strictly true as a general rule. This the true relationship has another factor.

    This factor while not large here will be critical at lower angles, for example if you reduce the angle to 10 dps you do not get this huge advantage of predicted which would be 80+% as it is likely the 10 dps edge would start to roll in these knives and would chip in other knives and thus there is a tan (angle)^n factor which has to be considered.

    If you reduce down further to 5 dps then the strength/toughness factor would be so dominant the performance would reverse in high carbide steels. If you go even lower the performance will suffer at any steel.

    If you had to make an informed guess, what would be the low range on the micro bevel angle for high carbide steels like S30V / S90V for light duty every day carry use?
    This is very sensitive on two questions :

    -what grit finish do you use
    -how sharp do you get and keep the blade

    These effect the answer by :

    -as the grit finish is lowered the angle tolerance is lower
    -as the sharpness tolerance is lower, the angle tolerance is lower

    For example people who want to get a true smooth shave have often found that S90V need to be 25 dps to get a true razor sharpness.

    I use 600 DMT often as a working finish (mainly because I have the hones, I think 1200 is more optimal) and I find 15 dps to be acceptable but it does have chipping damage in both, less in S30V.

    However if I increase the angle to prevent the chipping the cutting ability and edge retention decreases so I don't see the point. This is one of the reasons why aside from experimental pieces I don't use high carbide steels as actual working blades.

    I do a lot of experiments though and have a ot of those blades, I am getting a 70 HRC custom in Cowry-X now.

    Quote Originally Posted by dbcad View Post
    The old ~1060 knife will get a nice low edge angle
    I made the argument years ago and I still think it is valid that one of the major reasons edge angles have more than doubled is the increase in carbide volume. I sharpen kitchen knives for friends and family all the time and there is a huge difference in how the old ones and the new ones are sharpened. On the old ones the angles are so low you can't even see the difference between the primary and secondary bevel.

    Quote Originally Posted by _centurio_ View Post
    ..the tested knives made of S110V, S125V and Cpm 10V, have to many/large carbides for a 30 cutting edge (too less matrix to hold carbides stable).
    Yeah there are a few things I need to add to the table to reflect this :

    a) time to shape
    b) time to sharpen

    as the first one is influence (reduced) by not only the carbide volume directly but also by the fact those knives take much more damage. To be specific just look at a few examples :



    That is a custom O1 blade from cKc knives :



    S35VN 59/60 HRC Peters



    S30V 60 HRC Wilson

    There are some things I should clarify though, first among them is that these edge retention comparisons are stopped when the edge retention is below 5% of optimal. While that sounds low, it only is because the starting sharpness is so high. At that point the edge still slices newsprint for example.

    If you do edge retention comparisons to very low levels of sharpness where you can't even cut photocopy paper for example then the high carbide steels will start to catch up because at some point the edge will stop fracturing once it has worn to the point it has enough thickness to retain the carbides.
    Last edited by Cliff Stamp; 11-28-2013 at 05:30 PM.

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    Quote Originally Posted by chuck_roxas45 View Post
    Thanks. It's been awhile since I checked that thread.

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    Spyderco Forum Registered User Brock O Lee's Avatar
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    Thanks for the detailed explanation Cliff...

    Quote Originally Posted by Cliff Stamp View Post
    -as the grit finish is lowered the angle tolerance is lower
    I never gave this much thought, but intuitively it makes sense that a very coarse edge would chip out (or break a tooth, so to speak) easier than a smooth one.

    Quote Originally Posted by Cliff Stamp View Post
    I use 600 DMT often as a working finish (mainly because I have the hones, I think 1200 is more optimal) and I find 15 dps to be acceptable but it does have chipping damage in both, less in S30V.
    I think this answers my question, and confirms my suspicion that I would not want to go much lower than 15 dps micro bevel, or much coarser than SM medium on these high carbide steels, for my usage.
    Last edited by Brock O Lee; 11-29-2013 at 03:03 AM.
    Hans

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    Brock,

    It is very dependent on the how and what you are cutting, very soft and abrasive materials can be well suited to a very low angle/coarse edge (cardboard, ropes) but very hard materials are not and require a higher polish and a higher edge angle. It just takes a little experimentation to find the smallest edge angle which resists rolling that you can see and the smallest micro-bevel which stops premature collapse of the edge. It is very easy to tell if the micro-bevel is too low as the edge will flatten almost instantly. If you turn the knife sideways it looks fine, but if you look down at the edge you will clearly see it reflect light.

    If you are a bit concerned about grinding up a decent knife then all you have to do is get a couple of cheap ones, it isn't hard to pick up a low and high carbide steel, just get something basic like a 440C blade and a basic carbon steel knife and grind both of them down to where they fail and see where it happens. Any decent knife then has to be able to reach at least those levels so you can use them as lower bounds.

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    Quote Originally Posted by 3rdGenRigger View Post
    ... You go everywhere sideways in slow motion and it's epically good fun if you're a keen driver....
    LOL I thought you were insane until I got to the punchline. Pretty much all I drive is a pickup.

    And the snow comment is funny, too. We've had snow on the ground for a while now and I live about 1000 miles south of you, within an hour's drive of the Spyderco factory ...

    Gordon

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    Spyderco Forum Registered User chuck_roxas45's Avatar
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    Ohhhh good snow job guys.
    I always heard that you catch more flies with honey than with vinegar, but then you catch even more flies with poop



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    So what happens when you incease the polish and switch to using push cutting as a measure of sharpness? Say you incease the polish to a Spyderco fine or ultrafine and test sharpness by measuring force to push cut thread on a scale?

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    Quote Originally Posted by me2 View Post
    Say you incease the polish to a Spyderco fine or ultrafine and test sharpness by measuring force to push cut thread on a scale?
    I have done that informally, but not to this extent. The main reason I have not done it is nothing more than :

    -the time it takes to measure the sharpness is much higher
    -blunting media are not as dramatic in push cutting typically

    I have done trials carving woods for example, and literally 1000+ cuts will not significantly blunt even a sharp $5 knife if sharpened properly, with local woods anyway. One of these days I will get a large amount of stock of something suitable and I will run that experiment.

    In the mean time the predicted results would be similar based on the same effects as noted. The main difference would be that the carbide volume is even more of a detriment in push cutting as all fracture directly lowers performance, in slicing it can increase it somewhat.

    This is so dramatic that steels such as 10V and similar will far less than O1 and similar in wood type cutting simply because of lack of edge stability.

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