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Edge retention with different grit finishes on 3Cr13 stainless

Posted by CliffStamp 
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Re: Edge retention with different grit finishes on 3Cr13 stainless
November 09, 2014 03:25PM
Fine India :

If there was a "super stone" this is likely to be it, especially in the west where it is praised heavily by ABS makers and a lot of people who use carbon steel knives. It is loosely rated as 320 grit / 37 micron and it produces an extremely coarse edge. This is a 15 dps micro-bevel on the EE chef's knife :



and it wears very slowly slicing 1/2" hemp rope as all those teeth just wear slowly away :



It produces the same kind of edge retention as the 320-Suehiro but it is far easier to set the apex :



There is an issue here I will talk a bit more about in the thread on the stone I will put up shortly and there is another point in that graph which should stand out strongly as well which is due to the same issue.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 09, 2014 06:12PM
The panacea of sharpening stones. Yay!

Did you use it wet, dry, or oiled?

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Folding knives are fun, fixed blades are important.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 10, 2014 01:26AM
I use it with water treated with an anti-rust compound : [www.cliffstamp.com] . It isn't likely ideal, I am just playing around with micro-bevels, there is so little grinding it doesn't matter. I am going to use the coarse side shortly, I just have to pick up some more rope. On that side I am going to use an actual honing oil, a degreaser and just water in various experiments.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 10, 2014 01:28AM
Cliff is this a Norton India stone?

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Re: Edge retention with different grit finishes on 3Cr13 stainless
November 10, 2014 02:40AM
Yes, I am planning on picking up the silicon carbide ones at some point to complete the set. I actually ordered them with it but they were out of stock.

--

As a couple of corrections to points made in the above :

Steel Drake asked about the influence of the edge finish or it came up in conversation. I made a point that putting the coarse apex on a coarse edge would likely give better edge retention because it would be rougher. This doesn't turn out to be the case. The edge retention isn't degraded if the edge is polished, in fact the cuts are actually easier (slightly) if anything due to reduced friction.

Collin made a point about would the soft hemp really smash in a coarse edge on a push cut, well this turns out to not be as simple as you might think. I have done a few runs with push cutting and the problem is that a push cut with a coarse edge isn't very efficient. The force easily ramps up to over 50 lbs, in fact it isn't that much under it when they knives are freshly sharpened. As the force climbs over 50 lbs then it isn't that easy to keep this very slim blade actually straight in the cut and when it is twisting not only can it damage the apex, it often damages the edge itself.

For example, the Fine India has a TCE of > 4 in on a slice with a 2" draw, this represents ~ 500 slices. The edge is undamaged, can still easily slice papers, cuts the hemp with ~20 lbs and shows at most some slight light reflection. However on a push cutting trial after ~10 cuts (it varies) the edge can be damaged visually, the force to cut the hemp is >> 50 lbs and you can't slice anything as the edge can be warped. But again this is happening because the force is so high the actual blade itself bends in the cut and thus the edge twists.

It is sort of obvious that if you are doing push cutting to any extent than ultra-coarse finishes can't be used because you can damage the edge on just a few push cuts on hard cutting and thus the combination edge retention would be ultra low. I am still playing around with the numbers, but might have to switch to another knife to do a full comparison. I need to do some high polish runs as well.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 11, 2014 05:36PM
Coarse India :



Which is rated at 93 microns (again don't take that to be overly precise) which seems sensible if you look at the size of the holes/abrasive compared to the fine India :



This produces a very coarse edge :



which again wears in that very slow multi-step pattern :



That is the edge at < 1.5% of optimal, ~1000 slices, but it still has a lot of life left in it, still can slice newsprint for example.



I never really intended to be this specific with the chart but I think I am going to do some more runs with each to see if I can explain, or at least cement some of the interesting points :

-is the diamond so high compared to the CBN simply because the diamond is new and the CBN is used

-is the Sigma Power relatively low compared to its grit because it is worn or is it starting to see the loss of performance in extreme lower grits

There are two major influences :

-the size of the teeth, which increases edge retention
-the sharpness for lack of a better term of the edges of the teeth, which I believe decreases it

In very low grit finishes I think the second one over powers the first but I need a lot more data to support that. At this stage it is just a weak hypothesis.

--

In regards to push cuts, it really isn't practical with this finish. I tried a straight push, the force is ~60 lbs, even with a rocking cut it takes ~50 lbs. These kinds of forces are so high that the knife is blunting from the lateral forces on the edge more so than the hemp abrasion. This can be so strong the edge can fail in just ~10 cuts whereas on a slice it easily does ~1000 and has no visible damage and barely any visible blunting.

--

As a general aside, it takes a long time to do the really coarse grit runs as they take ~1000 slices so doing five of them requires on average (and this is kind of amusing) 100, 000 lbs of force applied.

It might not sound like a lot for example to do an arm curl with say 20 lbs, but try doing 5000 reps with it sometime. I was curious the other night at the end of watching a movie why my hand was cramped until I realized that I had just done 1500 reps of essentially ~15 lbs wrist curls.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 12, 2014 12:39AM
Spyderco Fine :



This is interesting. When I did the Medium I wondered why it went as low as it did and the fact that this one is relatively low as well makes me really curious. The unfortunate thing is that I should have measured the push cutting sharpness the same time as I did the slicing runs as this would have ruled out an obvious possibility. In any case i have started doing it now and will note them in the future and update a push cutting shart even if for now I just do sharpness and not edge retention (for reasons noted in the above).



This is the edge after the hemp cutting. I have drawn a line at the micro-bevel point, it is finished with the 2000 Naniwa Aotoshi below it. Interestingly enough there is a lot of deformation in the apex which itself raises some interesting questions.

In regards to push cutting, here are some sharpness measurements which are the forces in grams to cut Espirit Baisting thread :

-Spyderco Fine : 40 - 45

-Fine India : 210 - 220

-Coarse India : 250 - 260

These are based on one sharpening run so don't give these that much confidence but they they make one point because :

-CBN (worn) :190 - 200

Now I just have to see if the Diamond is much higher (which means the sharpness is lower) and then repeat it with the new side of the CBN rods and make sure that all checks out.

These numbers can be used almost directly to measure the coarseness of the finish much better than the slicing sharpness because that is a combination of two movements.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 14, 2014 12:16AM
I have been looking forward to this one for a long time :



This is 80 grit drywall sanding screen, it is extremely coarse, so much so that I have to shoot it at 5X magnification to get it in focus. If I try 50X then there is depth of field issues and I can't bring the abrasive into focus evenly :



+



Now to clarify, this is NOT meant as a knife sharpening abrasive (surprise), it is designed for the purpose of sanding drywall (hence the name) and the screen is used to prevent loading and keep it cutting. There are also some interesting problems in sharpening because the grit is so large it is actually up off the mesh so high that the knife will cut into it and hang up. I tried edge-into sharpening a few times and could almost get it work but you could hook the edge and then it would drag along one of the big chunks and just be cut off. I had to resort to edge trailing sharpening.

I only did a few trials, but the sharpness on both a slice and push are really low. It is also hard to experiment with technique because it removes metal so fast (this is silicon carbide, insanely aggressive) that the micro-bevel becomes a visible bevel almost immediately. I am going to play around with it a bit more. The sheets are about ~$1 so they are not that expensive but I think there would be better choices for knife sharpening. In fact if you wanted to experiment with these then find a drywaller and sharpener their knives. They tend to replace them when they are clogged and they are usually easy to clean and then reuse.



The edge is decent and wears slow :



But it can't match the mid-range abrasives for total lifetime :





I am slowly putting the push cutting measurements together and will add them to the chart shortly by adjusting the order of the stones by that vs the micron size. The reason for this is because some of those results are on worn stones and they are producing finer edges than the grit size would make you expect :



-Spyderco Fine : 40 - 45

-Spyderco Medium : 70 - 80

-Soft Arkansas : 90 - 110

-Fine India : 210 - 220

-CBN (worn) :190 - 200

-Coarse India : 250 - 260

-80 Drywall Mesh : 380 - 420

I think what is happening is the idea I proposed earlier, that the x-coarse edges simply can't make actual sharp teeth. Thus the performance increases only up until a point and then starts to decrease as while the teeth get bigger they themselves get duller. Think of the teeth of a sharp vs that of a cow type thing.

Too bad this happens as otherwise you could get near infinite sharpness by using 2-4 grit silicon carbide abrasives, but it should be obvious that can't happen anyway. I also think I have a strong predictor of total performance if I try to correlate edge retention to this :

-sharpness on a slice / sharpness on a push

I need a lot more data though before I can even begin to do those calculations. However if I can and this work is it pretty interesting because it means I can actually predict the edge retention based on two sharpness measurements. Now if I could only figure out how to do that for steels.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 14, 2014 12:33AM
How do you see the results of this experiment affecting future experiments?

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Re: Edge retention with different grit finishes on 3Cr13 stainless
November 14, 2014 12:46AM
Mark,

The big thing to me right now is that it calls into question what edge retention even means in regard to steels let alone the value of measuring it in the common ways. If this doesn't stand out to you then just consider this :

- ~1000 cuts on 5/8" manilla rope is argued by some to extremely high and often argued to be achieved with ultra-high performance knives (10V customs with 60+ HRC)

Now lets step aside for the moment on the validity of that claim and lets just assume it is at least a rough kind of benchmark as a point of comparison.

Well I can do that easy with this 3Cr13 blade which costs ONE DOLLAR and that isn't even the optimal performance as the micro-bevel angle I am using here (15 dps) is too high. What does that say about the value of measuring edge retention on a slice on abrasive media and not again I am just looking at grit, not even trying to optimize geometry which is pretty bad in this blade because it is a single bevel (no primary grind).

Now in retrospect Roman made this exact argument years ago which is why he argued that if you wanted a high performance knife then you looked at steels which had high apex stability. If all you want is edge retention on a slice to low sharpness then you can get that with anything by just using a really coarse edge anyway so what is the point of maxi-maxi steel.

Plus lets be frank here, when is the last time anyone made 1000+ cuts into clean rope or cut 1+ km of cardboard and didn't hit something which damaged the edge. Do these kind of statistics really matter compared to something like Kyley suggested which is a time scaled performance. If you take Kyley's approach then the argument becomes even stronger - use simple steels.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 14, 2014 01:30AM
I suppose the harsh reality of all of this is , if people use knives on a regular basis for cutting materials that may be dirty i.e. Construction work, than a simple steel sharpened on what ever gets the edge sharp the fastest it the way to go. If you need a fine edge as a chef for example than a fine grained steel with high apex stability would be the ideal choice. And if you are a collector or have mall ninja fantasies then who really cares what steel/grit finish/edge angle you have anyways.

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BIGFOOT FINDS YOU, YOU DON'T FIND BIGFOOT!



IT IS THE E-NEP THROWING BROTHERHOOD
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 14, 2014 03:19AM
I can't argue against that based on data/metallurgy, it just seems like there should be some use for high carbide steels. Maybe it is just my internal bias speaking because I have so much of it.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 14, 2014 11:28PM
Quote
CliffStamp
I can't argue against that based on data/metallurgy, it just seems like there should be some use for high carbide steels.

Hello,
excuse me for being a wisen hymer but how about "excellent steel for plastic injection feed screws, barrel liners, screw tips, and mold cavities , especially for plastic resins which contain abrasive fillers. Other applications include food processing equipment, pelletizer knives, granulator knives." "service in blanking & sizing dies, shear blades,
cold and hot forging punches, powder compaction tooling and many other applications where a combination of strength,
wear resistance and toughness is required." "Typical applications include form tools, broaches, milling cutters, hobs, and any special cutting tool where high hot hardness is required. " from Latrobe.
"Plastic Injection and Extrusion Feed Screws and Dies
Non-Return Valve Components
Pelletizing Equipment
Wear Components for Food and Chemical Processing" from Crucible

could not find any recommendations using these steels for fine edge, high sharpness cutlery.
scott



Edited 1 time(s). Last edit at 11/14/2014 11:29PM by oldsailorsknives.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 15, 2014 01:19AM
Quote
oldsailorsknives
....
could not find any recommendations using these steels for fine edge, high sharpness cutlery.

No argument with that.

--

As an amusing interlude, my cousin dropped down and wanted to borrow some money. I told him he could have it if he could sharpen a couple of kitchen knives. He accepted and I gave him a crash coarse on abrasives and 3-step sharpening (aluminum oxide vs silicon carbide, edge vs apex). I then put out a few stones and ask him to pick the two he wanted and explain why. He points at the 80 mesh drywall screen and that is where it gets a bit interesting :

"No, that won't work well"

"Why, it is really coarse and made from silicon carbide. It should cut the steel fast."

"The grit is so coarse the apex will tend to catch into it and damage it heavily."

"I thought you said silicon carbide is not tough and it will just fracture and produce sharp edges why doesn't it cut the steel."

Good question. The answer is that I was using so much of a draw that the force against the grit was not high enough to make it cut which is fairly high at a coarse grit as more surface area means more force is needed to generate the rupture pressure.

With this in mind I did some experimenting and tried edge into sharpening with very little lateral movement and was able to avoid the problem of catching and the sharpness was much higher than before. Now to be clear it is still low, about 20% at best but it was 5-10% previously, and combined with this the push cutting sharpness decreased (the edge was more coarse). With this in mind the edge retention factor (for slicing) seriously increased :

ERF (slice) = (sharpness on a slice) / (sharpness on a push)

This predicts that the edge retention on a slice should seriously increase and it did, going from a TCE of ~3 to one of about ~8 . I am going to do a few more trials to confirm the behavior, but it looks like this might not be so bad of a coarse abrasive for both speed and edge retention on a slice.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 15, 2014 02:18AM
I'm not understanding how the draw lowers the force on the grit.

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Re: Edge retention with different grit finishes on 3Cr13 stainless
November 15, 2014 07:53AM
I doubt it would be as simple as the force applied divided by the area on the stone that the knife covers when doing a draw.
Perhaps with less lateral movement you can concentrate more on the downwards force

It is always interesting to get new insight on stuff which you hadn't thought on




One question remains: Did he ever sharpen the knives?

_______________
Coffee and Blood
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 16, 2014 02:18AM
I am slowly working through the other grits and there are a few interesting observations :

-the waterstones are very consistent, some of the others, not at all

I am going to look at this in more detail elsewhere, but some of the other stones wear so fast that the results change consistently. The coarse India stone for example I am confident if I did ten runs would show a slow and steady decrease due to loading/wear, the drywall screen the same, though slower. The CBN/diamond would also show the same, but even slower. Now this is in general sort of known as people often refer to stones "breaking in" and getting finer. However the dramatic effect this has in reducing edge retention on a slice can be pretty significant, easily similar to comparing 420J2 to 420V for example.

Push cutting sharpness :

-Spyderco Fine : 40 - 45

-Spyderco Medium : 70 - 80

-Soft Arkansas : 90 - 110

-Suehiro 'Chemical' : 210 - 230

-Fine India : 210 - 220

-CBN (worn) :190 - 200

-Coarse India : 250 - 260

-80 Drywall Mesh : 380 - 420

I did a little work trying to get very high sharpness with the Suehiro, it is possible but much more time consuming than with the fine india which gives the same level of coarseness to the edge.

--

Quote
Shurdi3

[...]

Did he ever sharpen the knives?

Surely you jest.

Quote
C Amber
I'm not understanding how the draw lowers the force on the grit.

It doesn't really, I wrote that poorly.

When I am sharpening I generally do a sort of loose draw of the knife both down and across the stone so I can get most of the knife on a single pass vs sharpening in sections. This means I exert a certain amount of force both down the stone and across it. If the apex hits a large protruding grit then the force to make it cut can be higher than the force I am applying in the down direction hence the blade stops moving down but the other part of the force which I am exerting to the side isn't opposed and so the blade keeps moving it across the stone and thus the apex is cut off. If instead I do more of a pass straight down the stone and the apex hits the same grit then I just increase the force and it cuts into the apex.



Edited 2 time(s). Last edit at 11/16/2014 02:23AM by CliffStamp.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 16, 2014 05:27PM
Added 600 DMT :

Push cutting sharpness :

-Spyderco Fine : 40 - 45

-Spyderco Medium : 70 - 80

-Soft Arkansas : 90 - 110

-Fine DMT : 130 - 150

-Suehiro 'Chemical' : 210 - 230

-Fine India : 210 - 220

-CBN (worn) :190 - 200

-Coarse India : 250 - 260

-80 Drywall Mesh : 380 - 420

A little experimenting with this and I noted that the loading of the stone could also make a dramatic difference. I could make the edge retention on the fine DMT a lot lower (50%) just by not cleaning it. This was again reflected in the in ERF. The loaded stone would produce a higher push cutting sharpness and thus lower edge retention on a slice. The interesting thing isn't that this happens as it is kind of basic why it would be expected, but that this difference in edge retention (50%) is huge compared to what you would see from steels. This again likely explains why you often get odd/conflicting results because not only the grit can have a dramatic difference, even small changes like loading can easily be larger than steel influences.

--

As an aside, back in 2003/4 I measured the push cutting sharpness of a new Fine DMT rod it was 150 (5) so the plate I have has shown little wear over the years, especially given that it is what I use on almost all benchmark comparisons.



Edited 1 time(s). Last edit at 11/16/2014 05:29PM by CliffStamp.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 16, 2014 05:48PM
cliff sorry, i think i missed a post somewhere what is this new chart as shown above? just a link is fine

thanks

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Re: Edge retention with different grit finishes on 3Cr13 stainless
November 16, 2014 07:03PM
Quote
Mark a

... what is this new chart as shown above?

Do you mean the table? It is the push cutting sharpness (grams of force to cut Espirit baisting thread). I need to invert it to make a percentage, I will do that once I check the high polishes. The problem I was having is that I was ranking the finishes by the grit size of the stones in the edge retention chart, but for many reasons stones don't produce an apex coarseness simply based on their grit rating. The push cutting sharpness is a direct measure of the coarseness of the apex (if it is properly sharpened). The lower the push cutting sharpness the higher the apex coarseness. Of course the apex again has to be sharpened, hence why I have to measure the sharpness on a slice and push, if both are low it means the knife is just not sharpened well.

The easiest way to think of it is like a saw. If you have a 6 tpi saw then even when the teeth are sharp it takes more force to push it into the wood. Thus if you could not see the teeth on a saw, but you could measure the force you had to push down on the saw you could estimate the TPI. That is basically what I am doing.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 16, 2014 11:43PM
Added Bester 700 and MXF DMT :

Push cutting sharpness :

-Spyderco Fine : 40 - 45

-Spyderco Medium : 70 - 80

-Soft Arkansas : 90 - 110

-MXF DMT : 120 - 130

-Fine DMT : 130 - 150

-Bester 700 : 220- 230

-Fine India : 210 - 220

-CBN (worn) :190 - 200

-Suehiro 'Chemical' : 210 - 240

-Coarse India : 250 - 260

-80 Drywall Mesh : 380 - 420

This explains why the MXF DMT is so high slicing edge retention wise, it simply produces a much more coarse finish than the grit rating. This also can be seen in the initial work on the stone which shows random coarse scratches, hence the relatively high slicing edge retention. Of course the exact same thing is why lots of people complain about it like the razor guys because those coarse scratches reduces push cutting ability.

The Bester 700 is interesting as it produces a much more coarse apex than the fine DMT even though the grit ratings would suggest otherwise. However the DMT is well worn and the Bester 700 is always coarse lapped, which brings me to another point. The edge retention on a slice is so sensitive to apex finish that the edge retention with stones is even significantly influenced in some cases by the last lapping finish if the stone wears so slowly it can retain surface texture.

This also raises a point about edge comparisons in general. If the difference in edge retention slicing ropes/cardboard and such between say ATS-34 and Elmax is similar to the difference you see between apexing with a Bester 700 lapped with a coarse grit abrasive vs a finer one then what does it say about the value of that steel performance difference? As well what does it mean about claims because a lot of stones wear significantly as soon as you start to use them.

If for example if I took a freshly lapped Bester which was flattened with a very coarse abrasive and I used it to apex five knives, by the time I got to the fifth one the surface of the stone would be so much smoother that difference would likely be far larger than the difference in the steels being compared.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 21, 2014 05:51PM
Maybe these results, with a cheaper, softer knife/steel, is showing the sorce of the idea that you can get you knife 'too sharp' and it will go dull. Also, there seems to be a general consensus that for cheap/soft knife/steels, the best advice is to have a semi-coarse finish on the edge. I am only a quarter of the way of reading this thread, and I read the Spyderco thread, so this is a preliminary view.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 21, 2014 06:22PM
Quote
jasonstone20
Maybe these results, with a cheaper, softer knife/steel, is showing the sorce of the idea that you can get you knife 'too sharp' and it will go dull.

This is one of those ideas which has an element of truth but causes a lot of wrong ideas as well. It comes down to what people actually mean. I don't think it makes any sense to say a 10, 000 grit edge is sharper than a 10, 00 grit edge simply because it has a higher polish. Would you say that a 30 tpi saw is sharper than a 6 tpi saw just because it has more tpi? If not, then why would you say the same thing about the edge on a knife.

A very coarse edge, in general, with some caveats, will last long on slicing soft media. However it can fail dramatically push cutting hard media. So do you describe it as having high or low edge retention? I think the terms are simply too vague. Edge retention is specific to the type of cutting and material and we simply need to realize that and speak accordingly.

The other big problem with that idea (make a knife too sharp and ...) is that often people use sharp to mean cutting ability and they mean you can make an edge and/or apex angle so low that it will not have the strength and will just fail due to deformation. This is true, but it doesn't mean that you could leave an edge with a burr and not make it shave because that makes it fragile.

Again it is a terminology issue where the same word is being used in different meanings and there is conflict even when the argument appears to be sound. The famous example is :

"Evolution is a theory right?"

"Yes?"

"I have a theory that Wilt Chamberlain is a robot."

"Ok."

"Do you believe me?"

"No."

"So why should I believe your theory of evolution that says my great great great .... great grandfather was a banana?"

"Maybe because you have the same mental capacity ?"

Theory is being used in two very different ways there.

Quote

Also, there seems to be a general consensus that for cheap/soft knife/steels, the best advice is to have a semi-coarse finish on the edge.

This is another one of those ideas where the idea is almost correct but fails short of the goal. It normally goes like this :

A guy has problems sharpening a cheap knife, he can't get it really sharp. He decides to forget it and just leaves it with the edge he gets from the first stone in his jigger/system. He uses it and finds the edge retention is actually pretty good. He then decides for cheap knives that is how you have to do it!.

The problem is that what he is seeing isn't something due to cheap knives, he is only seeing part of the idea. If you run the same x-coarse finishes on "better" steels then you see the same performance amplification.

--

As an aside, I have been playing around with this lately and am doing a run now which makes this whole exercise of edge retention on slicing pointless because I have figured out a way to sharpen this knife so you can't blunt it on slicing hemp. I have done well over 1000 slices with just a 2" draw and had very little effect on the edge and it doesn't look like it is every going to give up slicing newsprint. I even switched to cutting on top of PT spruce to try to speed it up and it ignores that as well. If this trial ever ends I am going to repeat it one more time (what fun) and then post up how I did it and why it works. It dominates any kind of slicing edge retention anyone has made on high carbide steels and it isn't even close. I am pretty sure I could easily do that Boye picture of the big pile of rope.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 21, 2014 11:14PM
Quote
CliffStamp
I don't think it makes any sense to say a 10, 000 grit edge is sharper than a 10, 00 grit edge simply because it has a higher polish

I was under the impression that as the edge finish gets finer, the average thickness of the apex decreases. It makes sense as I visualize a fine removing scratches from a coarse edge, but I don't know how to put it into words or whether I'm imagining correctly. At any rate, that would be one pretty clear sense in which a finer edge is sharper.

Quote
CliffStamp
Would you say that a 30 tpi saw is sharper than a 6 tpi saw just because it has more tpi?

Doesn't the finer abrasive not only had more teeth per length, but also reduce the thickness of the teeth (because it doesn't bite into the steel as deeply)? If the saw had finer teeth as well as more, I could see that being described as sharper. Not sure, just thinking out loud here.

That "argument" against evolution is just a straw man, right, I mean nobody really argues against evolution like that, do they? Even if you hold fixed the meaning of evolution in that line of reasoning, it's terrible! But I try to stay out of the anti-evolution trenches, maybe it's really that bad.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 21, 2014 11:29PM
Quote
ianevans
Doesn't the finer abrasive not only had more teeth per length, but also reduce the thickness of the teeth (because it doesn't bite into the steel as deeply)? If the saw had finer teeth as well as more, I could see that being described as sharper. Not sure, just thinking out loud here.
I would only describe the indivual teeth as being sharp. Since they have an actual edge. Saws have more going cuttingh wise than knives, so TPI is telling you something about the saw other than sharpness.


Quote
ianevans
That "argument" against evolution is just a straw man, right, I mean nobody really argues against evolution like that, do they? Even if you hold fixed the meaning of evolution in that line of reasoning, it's terrible! But I try to stay out of the anti-evolution trenches, maybe it's really that bad.

I've seen sillier arguments presented by people who were quite serious.

Re: Edge retention with different grit finishes on 3Cr13 stainless
November 21, 2014 11:44PM
Quote
ianevans

I was under the impression that as the edge finish gets finer, the average thickness of the apex decreases.

If properly sharpened it will yes.

Quote

At any rate, that would be one pretty clear sense in which a finer edge is sharper.

Why, serious question, not trolling.

Here is what I would ask, if I gave you a two knives and you used them what physically are you feeling / measuring / judging to say which one is sharper. People do this all the time without a second thought to rank sharpness but for some reason when they think about trying to quantify it they forget all about it.


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Doesn't the finer abrasive not only had more teeth per length, but also reduce the thickness of the teeth (because it doesn't bite into the steel as deeply)?

Now this is a really interesting question.


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I mean nobody really argues against evolution like that, do they?

Yes, they really do, it is one of the classics - but there are better ones, much better. My favorite is the argument that goes similar to :

"Well if you want to prove to me that evolution is true then show me a cow which gives birth to a whale!"

"Ah, that doesn't happen."

"See, evolution isn't real!"
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 21, 2014 11:58PM
My phone is freaking out as I try to copy your "Why" question, Cliff, but I was thinking that , if sharpness is pressure required to make a cut, and pressure is inversely proportional to surface area, then the thinner apex is sharper.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 22, 2014 12:11AM
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C Amber
You're such a tease.

Since you asked nicely, I have not repeated this yet but will the next time I roll a critical :



That is the edge as sharpened, see if you can guess what made it. Here is the edge after 1000 slices :



Here is the problem, the edge is so coarse that it has significant depth that I believe that it is behaving like a serration. The "teeth" are also so large they do not easily deform and any fracture tends to leave them almost as sharp as they were in the beginning.

It took 1727 cuts to reduce it down to the level where I had decided to end the trials and that really isn't what most people would call dull, it could still easily slice newsprint for example and again I was cutting not only 1/2" hemp but into a PT block.

I had to switch to the block because of the sheer volume as free hanging cutting it harder to do (on me, easier on the knife). For a bit of perspective, just remember that is ~2000 repetitions of a down force of 10-15 lbs.

This is what I used to generate the edge :



This is 50X magnification, the grit is so large I can't really get it on screen. It also isn't that easy to sharpen because the grits are so large they are deep enough for the edge to catch even with direct perpendicular passes. Here it is at just 5X magnification :



Know what it is yet?



It is a 36 grit aluminum oxide sanding belt, the cheap kind, costs ~$1.50. I bought it to try as a lapping surface. I used it for an edge retention trial as a lark. I thought the performance would be poor because I didn't think it could sharpen the edge. However I spent a little time figuring out how to use it and the basic process is actually really simple :

-edge trailing
-ultra-light

It is just below shaving meaning you have to risk cutting your skin to cut hair, and won't push cut newsprint but slices it trivially. The push cutting performance of course is pretty horrible :

Push cutting sharpness :

-Spyderco Fine : 40 - 45

-Spyderco Medium : 70 - 80

-Soft Arkansas : 90 - 110

-Fine DMT : 130 - 150

-Suehiro 'Chemical' : 210 - 230

-Fine India : 210 - 220

-CBN (worn) :190 - 200

-Coarse India : 250 - 260

-80 Drywall Mesh : 380 - 420

-36 grit sanding belt (aluminum oxide) : 480 : 520


Here is the really silly part, this knife is poorly ground for cutting hemp as it has a wide single bevel and the apex angle I am using (15 dps) is too high. This means I could easily increase the performance if I actually put a primary grind on this knife and lowered the apex angle.

Now what does that mean about all the promotion of high carbide steels if this $1 knife can do that many cuts with an off geometry and still slice a piece of newsprint and remember I am only using a tiny bit of the edge.

It is obvious to me that the common way that edge retention is talked about simply makes no sense at all because simply saying "uber-v steel is excellent as I can cut Y amounts of cardboard/rope" is nonsense because you can do a massive amount with any steel.

What does high edge retention mean then in regards to the steel itself and what is a reasonable way to determine it.

Again just think about the fact that if I used the entire edge, even with this really low performance geometry I could cut 10, 000 pieces of 1/2" hemp and still slice newsprint. The even sillier part is that the sharpening time is maybe 5-10 seconds to get back to the starting point.

--

Now again I need to repeat this again with this knife/steel, just to bound the results. But I have done this kind of thing before, one of the first extreme trials I ran was with a D2 knife with an ultra-coarse finish. I have even done it with unhardened mild steel.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 22, 2014 12:14AM
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ianevans
.... I was thinking that , if sharpness is pressure required to make a cut, and pressure is inversely proportional to surface area, then the thinner apex is sharper.

This is an excellent starting point, however what happens if you are talking about slicing, does this still hold? In particular what happens if you try to use that approach to looking at a serrated blade.
Re: Edge retention with different grit finishes on 3Cr13 stainless
November 22, 2014 12:35AM
You are a tease...what is rolling a critical? I know you use a die sometimes to decide what kind of work to do, but what is a critical?

And thank you for sharing. That's pretty damn cool...both that were able to use that to sharpen and the results.

Two questions:
Could a lower angle do better? Is it possible those "teeth" would be more fragile in a negative way at a lower angle? I'm guessing not since the edge angle is probably already pretty low.

Could one not still argue that a HCV steel would still do better if one could find a meaningful way to measure the negligible loss of sharpness? Like say do 20K to this steel's 10K cuts as the carbides would increase the toothiness and, in this case, productive fracture at the edge? Although of course they couldn't take advantage of the low apex angle like this steel could.

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