Rope slicing test CPM D2 vs. D2

[gunmike1]

I recently got the opportunity to compare a Spyderco Military in CPM D2 and a Mel Sorg custom in D2. I tested them for slicing edge retention on 5/8" manilla rope. The full write up can be seen here: http://www.cutleryscience.com/evaluations/d2_sorg_vs_cpm_d2_military/michael_c.pdf . I was trying to compare the steels more than the knives to see how different CPM D2 acted than standard D2. Basically the results showed that the steels were nearly identical in slicing edge retention when cutting the rope.

I got to handle the knives and EDC the Military for a couple weeks (my work doesn't look too highly upon carrying fixed blades every day, neither does the local town I live in) and squeezed the testing in when my busy schedule would allow. This was my first time doing any sort of formal, measured testing, so it was a learning process for me and I'm sure some things could have been done better, but these are the results I got.

Mike

 

[mmmotorcycle]

This is interesting..... Seems like spyderco didn't vastly improve on the D2 steel. Could you try this test with another Military? This might quantify whether Spyderco improved the Military's design. Oh and where did you get a hold of the new military? I've wanted one for ages.....

 

[gunmike1]

This is interesting..... Seems like spyderco didn't vastly improve on the D2 steel. Could you try this test with another Military? This might quantify whether Spyderco improved the Military's design. Oh and where did you get a hold of the new military? I've wanted one for ages.....

I am not sure what hardness the Spyderco CPM D2 is running at, but I know the Mel Sorg in standard D2 is reportedly at 62 RC. I would guess that the Spyderco is running softer than that, but until the knife is done being passed around for testing and it gets Rockwell tested we won't know for sure. How much difference the hardness is or would make is something I can't answer. And I would also add that it really isn't Spyderco trying to improve on D2 (I don't think they make anything in standard D2), but Crucible trying to improve on D2 and Spyderco giving the knife community a chance to try out a new steel with a sprint run knife. I don't have another Military on hand, but I do have a Manix that I was hoping to test if I ever get time to see how S30V (Rockwell tested to 58RC) as done by Spyderco compares to the CPM D2 when run at the same profile. As I said in the actual test link my wife recently had surgery so my spare time is very minimal right now, but I think that is a very valid question to compare the S30V version vs. the CPM D2 version of the Military.

I got the knives sent to me by Cliff Stamp as part of an evaluation group. I believe the plan is to ship the knives to everyone who is interested within the evaluation group for whatever testing they want to compare the 2 steels. The Spyderco was fresh out of the box when I recieved it (with the sharpest factory edge I have used), the Mel Sorg was well used. There were no testing directives or expectations given, basically the group is free to do whatever testing, formal or informal, that they please as long as they report their results and impressions. Truthfully I was caught by surprise when I opened up my mailbox to find these 2 knives in a nondescript package. I'm glad I got the chance to test the knives, however, as it was fun and a good learning experience.

Mike

 

[epistasis]

This is interesting..... Seems like spyderco didn't vastly improve on the D2 steel. Could you try this test with another Military? This might quantify whether Spyderco improved the Military's design. Oh and where did you get a hold of the new military? I've wanted one for ages.....

Basically his results show that there isn't much difference between these knives only. You can't conclude that CPMD2 and D2 are different based on one test with two completely different knives.

 

[sodak]

Nice writeup! I like your method, I can find Arrowhead bottles here. What kind of twine did you use, do you have a SKU? Did you cut through the entire rope at a time, or unwind the 3 major strands and cut them by themselves?

Thanks!

 

[Cliff Stamp]

Seems like spyderco didn't vastly improve on the D2 steel.

There are many aspects to steel besides slicing aggression edge retention (SAER). As the carbide volume is the same in CPM steels the only real enhancement to SAED would be in any extra hardness you can gain but few will push steels to that limit. The other aspects of interest would be push cutting edge retention (PCER) and issue with burr formation during sharpening and possibly corrosion resistance.

I believe the plan is to ship the knives to everyone who is interested within the evaluation group for whatever testing they want to compare the 2 steels.

Yes, this is mainly to get some expereince actually testing with a rather interesting sample. Since this isn't blind testing there is some issue of bias, especially when prior results are knows, but I want to evaluate the influence of that as well.

-Cliff

 

[gunmike1]

Nice writeup! I like your method, I can find Arrowhead bottles here. What kind of twine did you use, do you have a SKU? Did you cut through the entire rope at a time, or unwind the 3 major strands and cut them by themselves?

Thanks!

Thanks! I cut the whole rope, all 3 strands at once. I will try to dig up the SKU for the twine (I do remember it being medium cotton/poly), though it's probably like the rope as not being the most consistent of materials, especially when bought several states away. I personally think a better material than the twine can be found (lighter weight material that would require a lighter weight for sharpness checking), but it was the lightest rope/strand material Home Depot had on the shelves at the time and I bought it because I was in a hurry. Either way, I'd be happy to try to find the SKU and compare results and learn some of your methods.


Mike

 

[sodak]

No problem, I'll check the local HD. I want to see if I can perform almost the same tests. Hanging the water bottle was a great idea.

 

[Cliff Stamp]

It might be helpful to send sample of the test media along with the knives.

-Cliff

 

[gunmike1]

It might be helpful to send sample of the test media along with the knives.

-Cliff

Good idea. Next time I get to the post office I will ship some off to Sodak, as I have quite a spool of it.

Mike

 

[Cliff Stamp]

Once people get comfortable with various methods of testing sharpness it would probably be a good idea to buy a large quantity of the testing media and just ship it to those interested. The cost would be very low as these are all inexpensive materials.

Here is a reference to another CPM-D2 comparasion, this time against Friction Forged D2, this is slicing aggression on rope performed by Phil Wilson :

http://www.bladeforums.com/forums/showpost.php?p=4684224&postcount=17


-Cliff

 

[Sal Glesser]

Hi Mike,

thanx for the test and info. good stuff.

I would be interested to see the results of the tests done with a highly polished edge. One of the advantages of the CPM steels is the fine grain structure which is best shown with a very fine edge as opposed to a coarse edge.

sal

 

[gunmike1]

Hi Mike,

thanx for the test and info. good stuff.

I would be interested to see the results of the tests done with a highly polished edge. One of the advantages of the CPM steels is the fine grain structure which is best shown with a very fine edge as opposed to a coarse edge.

sal

Thanks, Sal. That was probably the part of the test that I looked forward to the most, but my wife had her arm surgery moved up by over a month on 2 days notice and thus I was left with no chance to test the polished edge retention. When I brought the knives up to a .3 micron finish from 3M lapping films the CPM D2 was slightly sharper than the regular D2 based on how far from the point of hold it would cut newsprint. How much that would even out over different sharpenings I'm not sure. I did carry and use the CPM D2 Military for a few days with the polished edge, and it seemed similar to my Manix in holding that polished edge for EDC stuff like breaking down a couple boxes, opening envelopes, and cutting some straps, but the cutting was so informal and haphazard (as is most of my EDC cutting) it is hard to even say how close the Manix and CPM D2 perform. Basically, it lost it's hair whittling ability fast like every other blade I've polished like that, but was still shaving after several days of moderate use. I really needed to do more formalized testing to try to draw any conclusions on the polished edge retention. Like I said earlier fixed blade carry draws a lot of attention in my parts, so I didn't get to EDC the Sorg or do much cutting with the polished edge on it due to time constraints, so I can't really comment at all on it's polished edge retention. Hopefully one of the future testers can look into this and give us some good feedback on how the 2 steels compare, as polished edge retention and resisting microchipping are 2 of the main properties that should make for very interesting comparisons between standard D2 and CPM D2.

One thing I can say for sure is that the ergonomics on the Military really worked for my hands with or without gloves, and the factory edge geometry was impressive for a 4" folder. The edge thickness was .019"-.020" along the edge and a bit over 13 degrees per side, with an edge that was cutting free hanging hair with ease. Definately the sharpest factory knife that I have handled, and I liked the design enough that I may be willing to overcome my dislike of linerlocks to get myself one of these knives.

Mike

 

[sodak]

Hi Mike,

thanx for the test and info. good stuff.

I would be interested to see the results of the tests done with a highly polished edge. One of the advantages of the CPM steels is the fine grain structure which is best shown with a very fine edge as opposed to a coarse edge.

sal

I have both of the blades now, and will get to this testing hopefully this weekend, but certainly in a week or two. Consider it done.

 

[thombrogan]

Sal,

Any chance you get Seki to make some knives in SKD-11? It's Hitachi's D2 and would be great to compare with VG-10 and ZDP-189 in a CalyIII format.

Gunmike1,

Thanks for the review!

 

[Greg]

I've got to wonder how much sharpening has to do with results, without taking into account different profiles and thicknesses.
I know with my own knives, as I get better at sharpening, (and I've been 'practicing' now for almost 50 years), each blade is getting closer to the same sharpness as the others. There is still a difference however, even on the two knives I have that are identical, when sharpened one right after another.
Greg

 

[Cliff Stamp]

I would be interested to see the results of the tests done with a highly polished edge. One of the advantages of the CPM steels is the fine grain structure which is best shown with a very fine edge as opposed to a coarse edge.

Yes, this would be one of the main predicted advantages of the steel, ease of taking a very high polish and holding it at low angles. Just a note, it takes a lot of time to compare knives in as much detail as Mike did. This is why I assembled a group of several dozen people so they can all look at different aspects and thus cover a broad scope of work as well as have most of it repeated by independent people.

One thing I can say for sure is that the ergonomics on the Military really worked for my hands with or without gloves, and the factory edge geometry was impressive for a 4" folder. The edge thickness was .019"-.020" along the edge and a bit over 13 degrees per side, with an edge that was cutting free hanging hair with ease.

Yes, it is an impressive knife, I would like to see that in 12C27M.

I've got to wonder how much sharpening has to do with results, without taking into account different profiles and thicknesses.

This is a very important point, the blades should be all checked for sharpness initially as Mike did to make sure they all start at the same sharpness. If this is not the case then it has to be confirmed that this is a limitation in the steel before proceeding. If this is not done then the tests could be unfairly biased infavor of the steel which has a higher initial sharpness.

-Cliff

 

[Broos]

Thanks for posting this test. I am having trouble thinking how some of the measurements were taken, though. The definition of sharpness you used here is length of the edge it took to cut a cord under tension. Initially they were using only 3 millimeters or so of the edge.

In my mind this seems a difficult test to achieve unifomity - it would be very difficult to achieve a cut at uniform speed and force (especially initially), and I think measuring the length of edge would be problematic. Especially down to hundredths of a millimeter.

Can you explain how this was measured? How did you record where the cut started and where it ended? Just with your eyeball or did you have another means to measure this?

 

[gunmike1]

Thanks for posting this test. I am having trouble thinking how some of the measurements were taken, though. The definition of sharpness you used here is length of the edge it took to cut a cord under tension. Initially they were using only 3 millimeters or so of the edge.

In my mind this seems a difficult test to achieve unifomity - it would be very difficult to achieve a cut at uniform speed and force (especially initially), and I think measuring the length of edge would be problematic. Especially down to hundreths of a millimeter.

Can you explain how this was measured? How did you record where the cut started and where it ended? Just with your eyeball or did you have another means to measure this?

Good questions, this was the biggest challenge of my test, trying to measure the sharpness and blunting. For each blade I made several markings (you can see some of those on the Mel Sorg photo, but those were only 4 of the markings made with permanant marker) along the cutting edge in pencil (which I had to reapply several times after cutting rope) so I would have a decent way of eyeballing the length of edge required to cut the twine. I would start at a mark, use the other marks as a reference by eyeball to where the cuts ended, and grab my digital calipers to measure the results right after the cut was made. While I am positive my numbers weren't accurate to the hundreth of a millimeter, my calipers are that accurate and I recorded the values that the digital readout displayed when I measured the distance to the best of my limited ability. I struggled with whether to just round them to a lower precision, but in the end I went with the raw numbers. The numbers are also the average of 5 sharpness tests per measurement point, done on 3 seperate runs. So, basically there were 15 different measurements that went into each of those sharpness numbers in the chart in the review. I felt that would help to even out my many systematic errors by taking so many measurements (inconsistencies in the twine & my technique are 2 of the systematic errors that jump out at me). Hopefully critical feedback and more testing on my part will help me to refine my testing to give more accurate measurements and sharpness tests, though this method seemed to work good for me on my first crack at measured testing.

As for the method, I tied the weight off on one end of the twine, used my right hand to hold the other end of the twine, and near the point of hold I would put the edge on the twine, slowly lift the weight with the blade to get the water bottle free hanging (I started with it standing on the floor) and make sure it wasn't swinging, and slowly and deliberately slice the twine once the blade was even with my hold hand in height. I did everything possible to avoid any downward pressure from my hold hand and swinging of the weight. After several trial runs where I adjusted the weight trying to achieve consistant results, and then seeing the blunting results and similar lengths of edge required to cut the twine also correlating with my newsprint, shaving, and finger pad testing I feel confident in the trend of the numbers. To what extent in absolute length of edge in millimeters they are accurate I don't know, but they were as accurate as I could measure as a newbie and the blunting trend and how different the numbers were between the 2 blades at each point was more what I was going for anyway, as opposed to getting lost in the absolute numbers at each point. My impression while doing the testing and trial runs was that the knives were just about identical in edge retention and initial sharpness, and the twine numbers I got back that up. I look forward to other testing results on these knives to see if they agree or disagree with my results so that I can take a critical look at my testing methods.

Mike

 

[Cliff Stamp]

I struggled with whether to just round them to a lower precision, but in the end I went with the raw numbers.

With all analog measurement you estimate the last digit. The true measure of the uncertainty will come in the differences seen from one measurement to another and then from one run to another. In this case the errors in measurement were so small you can not even see the error bars on the graph.

My impression while doing the testing and trial runs was that the knives were just about identical in edge retention and initial sharpness, and the twine numbers I got back that up.

It would be hard to argue why CPM-D2 would have superior slicing aggression edge retention assuming the hardness was similar because the carbide volume fraction is going to be the same anyway and thus the wear resistance.

An interesting conclusion can be drawn if you combine this work and the work of Wilson noted in the above. Of course the suppording data is light as it is just two knives, but if a=b and b=c, then a=c.

-Cliff