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Validity of manila rope edge retention testing
#1
I am about to embark upon some edge retention testing that I have not previously quantified with the BESS tester - manila rope cutting.

For my testing I plan to use 1" rope with a minimal wrap of insulating tape (just enough to overlap and completely cover). The use of the tape is three-fold; firstly to stop the rope unravelling, secondly to keep the fibres tightly together to try to make the material more consistent for each cut, and lastly to hopefully allow me to reduce waste by cutting off smaller sections as it is all held together.
I'd mark off a section of blade to 'saw' with, maybe 3" long, and cut onto a pine board.

Clearly I'm not proposing anything new with rope cutting itself, but maybe the full test process I'm going to use has not been tried.

What I have seen others do is to keep cutting (counting the cuts) until the edge won't get through the rope (or the effort is too high), or to cut a sheet of paper, cut the rope, and then cut the paper again, stopping when the paper is torn rather than sliced.

With the right slicing action I have been able to slice paper with an edge up to 400 BESS, so the paper test is not all that revealing to me.

My take on this is to instead introduce the BESS test perhaps after every cut of the rope (to be decided). Even if I never reach the point it won't cut the rope, I would have a log of cuts vs BESS.

There are many problems with this test including blade geometry, length of edge used in the cut, apparent effort (affected by the handle shape/size), batches of rope production etc, so I know it is flawed. To date, my work with the very controlled SET has found various anomalies and poor SET performances for blades that seem to do very well in real world use.

Has anyone already done this or have results proving or disproving the validity of rope cutting testing?
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#2
You might get some ideas from this video.  Start watching about 3:15 into it:
https://www.youtube.com/watch?v=bfp80sYH6iw

For the tape idea, you might consider taping on either side of the cut.  It seems that cutting through the tape could introduce adhesive which might effect the test and could even get transferred to the blade.

"cut onto a pine board".  Maybe put two boards next to each other and cut into the open space between them to avoid edge contact with the board.  A pine board will roll an edge and eliminating blade contact with the board would remove that variable.
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#3
Thanks, that video is very useful on many levels, but I'm not sure I want to build all of that jig, or follow the exact approach with weights. He has made his own BESS type sharpness measurement with the weight required to cut the smaller rope in one stroke.

The larger rope he uses has a wrap of some sort. It seemed quite papery and made me remember I had considered the rope being wrapped in masking tape.

Is the glue on the tape going to be a problem? If it is always there, at least it is consistent.

I do like that idea of not cutting onto a surface. Every other test I've seen has the rope sitting on a wooden board. Making it so the cut is into air removes any inconsistency of how much you cut into the board.
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#4
Thinking of the rope wrap, I'm considering trying artist's gummed tape. The type that needs water to make it sticky, so once dry this should not introduce sticky glue into the cut.
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#5
I don't know if the glue from the tape would be an issue or not.  It just popped into my head when I read your plan.  Duct tape for instance can gum things up pretty good.  I don't know if that would have any impact on edge retention or not.  Probably not.  Probably not worth worrying about.

I'm guessing fraying is not going to impact the results much, especially if you cut the rope between two tubes like the dude in the video did.  There are so many variables.  Also, I would think that conclusions derived from this type of test would be in big round numbers, "in the ballpark" kind of thing anyway.  You may feel differently, but if it were me I wouldn't fret over the details too much because in the big picture any small differences between tests would be undefinable and insignificant considering the broad and very general nature of conclusions that can be gleaned from this type of test.
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#6
So I watched some videos of guys doing edge retention testing with rope.  You're right Mr. subwoofer, they all cut against a cutting board!  

That seems highly problematic to me, considering the wood is much harder than the rope.  In many of the videos a "whack" can be heard as the knife impacts the wood, and a lot of pressure is used when slicing against the board.  I would think that impact would actually have more dulling effect than the rope.  

It's easy to show the dulling of wood impact on an edge.  Sharpen a knife and measure the sharpness.  Whack it a few times on a cutting board and do some slicing against the wood.  Measure sharpness again.  It doesn't take much to roll and edge!

In this video, you can hear the knife impacting the cutting board when the dude slices the rope: https://www.youtube.com/watch?v=C2CaE7pNe1M

It would seem to me that when devising a rope edge retention test, it would be advisable to construct it to avoid contact with any material other than the rope.
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#7
Agreed about keeping the cut only rope and not the board.

Now this is all very early and me doing a few things when I can while at work (fitting it in whenever I can). Interestingly, I've now done the first cut into paper wrapped rope (dried gummed paper, so no 'active' adhesive). Well, it was effin hard work. The wrap keeps the fibres tightly together so making it more like cutting a stick or something properly hard.

The first cut was in the middle of a long length, to take a section off for easier handling, so there will be a difference if only slicing off a thin piece.

Just thinking out loud now as I'm trying to see if there is anything worth continuing with. I still like the idea of the paper wrap. The guy in that video you linked to before has confirmed he uses masking tape and that he does have to clean up glue. Being 'active' rather than dried, the masking tape glue allows for some movement, but the gummed tape I've just tried goes stiff once fully dry.
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#8
Folks seem to go for rope or cardboard but there are other options that would be more consistent in thickness and composition.  How bout something like 24lb or 80lb card stock or layers of it?  With something like that the media would be more consistent, predictable and wouldn't have the fraying and other issues inherent with rope.

It would sure seem to me that to obtain any useful information consistent test parameters between tests would be required.  For instance, when comparing two different blades:
  • Consistent  media
  • Same initial sharpness
  • Same bevel angle
  • Same number of cuts
  • Same pressure applied
I've always thought edge retention testing is a tough row to hoe because there are so many variables.  That said, with sufficiently controlled test parameters it might be possible to have some confidence in the results.  To me at least, the only thing those Youtubers out there whacking of hunks of rope against a cutting board are accomplishing is wasting rope.
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#9
The first question in a research like this is: What we want to find out.
Edge retention by steel?
Edge retention by HRC, i.e. heat treatment protocol?
Edge retention by edge angle?
Edge retention by the sharpening method used, e.g. whetstone versus belt grinder?

The above has already been well studied by many, including Larrin Thomas using his CATRA tester - he has articles on each of the topic, e.g. https://knifesteelnerds.com/2020/05/01/t...fe-steels/

But if we want to find out the best performer in its knife category, the best designed knife for the function, then this makes all the above moments irrelevant.
Yes, absolutely irrelevant - because in this case we are testing the knife maker philosophy behind the cutting edge.
How companies design their blade for its function reflects in its performance.

We know that many knife makers heat treat even premium steels softer than the steel can take, that they design the blade with non-optimal thickness behind the edge, and give the edge poor performing angle.

If we test the knife as a whole, out of the box - a study like this could help to single out knife making companies who really strive for performance.
Because in the end, it is up to the knife maker to use the best steel for the function, heat treat it the right way, design the blade and cutting edge for the best performance, and sharpen properly.
http://knifeGrinders.com.au
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