What exactly is a CATRA Edge Tester?

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What exactly is a CATRA Edge Tester?

#1

Post by RustyIron »


I would like to hear from folks who have used an edge tester. I'm asking not because I NEED one, but because my brain compels me to measure and analyze things. I'm also a cheapskate, so I don't actually want to PAY for an edge tester. But I like building things, so if I knew specifically what and edge tester was measuring, it might set me on the right path.

First question: When someone tells me that their edge measures in at 125, it appears that they're measuring grams. It's just downward force imparted onto the the filament by the blade?

Second question: Is the gap of the test fixture and the tension of the filament specified as part of the testing procedure?

Third and last question: What is the test filament? Material and diameter, specifically.

When I started typing this post, it seemed a little daunting. I had to look some stuff up to pose the questions as precisely as possible. Now that I've learned a little, building a tester seems downright easy. I would appreciate some guidance and pointers for something I might be overlooking.

Thx.
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Re: What exactly is a CATRA Edge Tester?

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Re: What exactly is a CATRA Edge Tester?

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Thanks Dan
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Re: What exactly is a CATRA Edge Tester?

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Re: What exactly is a CATRA Edge Tester?

#5

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I've figured out the answer to what I wanted to learn. It turns out, I was curious about the BESS Tester. I assumed that it was some scholarly intentional consortium, like the Bureau of European Sharpness Standards. Nah. It ain't that. It's Brubacher Edge Sharpness Scale, invented by a dude named Mike. Mike came up with a simple and clever way to measure and compare edge sharpness.

I had seen pictures of Mike Brubacher's contraption, and it was so simple that I figured even a hamfisted galoot such as myself could whip one up for virtually no cash outlay. And now that I thought about it, I can. The hard part... the fun part... will be the filament fixture. I have plenty of aluminum and fasteners to work with. I found a potentially suitable scale already in the house.

The wildcard is the filament. A small roll is $25 from Mike B. I can afford it, but it's only important if I'm going to be comparing data with others. I'm not particlularly interested in that, at this time. I'll experiment with whatever filament I have on hand, probably fishing line. If I can find something that gives me the results I expect using utility blades and razor blades, then that will be good enough.

The usual descriptors used on the interweb forums such as "shaving sharp" or "hair-popping" are so subjective as to be almost meaningless. I think it would be REALLY cool if there was some kind of home-brew standard that could be used to communicate levels of sharpness. Rigging up a fixture out of a chunk of 2x4 is within everyone's skillset, and any experienced husband knows how to "borrow" his wife's scale out of the kitchen while remaining undetected. If there's filament that is cheap and readily obtainable, like Acme #12 Fishing Leader Line, then it might be possible have an inexpensive standard by which we can all communicate levels of sharpness.

Anyway, that's what's bouncing around in my head this morning. Gonna go down to the garage and see if I can gather up some materials.
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Re: What exactly is a CATRA Edge Tester?

#6

Post by RustyIron »

And...
Here's the guts of the project. It works as intended. I could only find two kinds of filament in the garage this evening. One isn't even in the ballpark. The other is giving me readings lower than expected, but it's close. Now it's just a matter of trail-and-error testing to find the right stuff.

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Re: What exactly is a CATRA Edge Tester?

#7

Post by kennbr34 »

If I remember right, Mike was inspired by another well-known sharpness tester (I believe it was Ankerson or Cliff Stamp over on BladeForums) who used fishing line, and there were a number of such contraptions popping up around in the early 2010s. As far as I remember, the reason Mike produced the BESS media is because fishing line was just too inconsistent for our purposes, even with the same manufacturer. A lot of guys at that time would end up looking at batch numbers to try to maintain consistency.

The initial prototype they used was the KN100, which was a much different contraption. I actually did some of the prototype testing for that device. The KN100 would suspend the filament above a cutting edge that was clamped down on the device, and then there was a platen above that you would place a cup on. You would rest the thread on the knife edge with no weight on the platen, and gradually add weight via supplied lead shot. One of the problems with this, is that the rate at which you added weight would greatly effect the results, because the loading was dynamic. In other words, if you took a 100 gram calibration weight, and stuck it on the platen and it cut the media, you could also gradually fill the cup with 100 grams of shot and it would not cut, and the difference was basically the sudden application of the 100 grams versus the gradual build-up. Because of that, the scores you get depend greatly on the rate at which you add weight. The other major issue that they solved with the PT50 was the loading of media in the yoke, because people found that depending on how taught you made the media could also greatly change the score; so the PT50 was designed to use disposable clips which had a consistent tension of the filament. I see recently they also released another yoke to use the media on a spool, and I'm not sure if they mitigated the issues of inconsistent tension, or if maybe those yokes are meant for "in-house" comparisons where the tester finds some way to maintain a consistent tension.

When they released the PT50, they changed the operation significantly, mostly to account for the difference in platen weight and filament tension. Instead of lowering the platen and a weight onto the stationary knife edge, you place the tip of the knife on a pedestal, and then lower the edge down through the test media. The problem with this method is that you need a scale that takes frequent measurements, and records the highest load read. An ordinary kitchen scale probably won't do the trick, because as soon as the media is cut, the weight will be released. You might then be tempted to keep a close eye on it and try to remember what the weight was when the clip severed, but depending on your own reaction time and the speed at which the scale will take measurements, you're likely to get inconsistent readings. This is one of the reason that the scale itself differs between their home and professional models, with some taking readings more more rapidly than others.

Not sure if you've found the thread by now, but here is the initial test thread on Bladeforums https://www.bladeforums.com/threads/edg ... r.1285538/

I have frequently thought that the issue of dynamic vs static loading could be pretty easily solved in the original design by using some kind of hopper to drop weight on to the platen more consistently than doing it by hand. So if you're going to go with an ordinary kitchen scale, you'll probably need to use the KN100's approach and apply the weight with a platen of some kind so that when the filament severs you don't lose your reading. Perhaps you could also figure out a more consistent way to load the weight too.

I still have my KN100 and use it from time-to-time, but ever since they changed the operation they also had to make a new BESS scale. With the KN100, the weight of the platen is included in the BESS score in the end, and since the platen weighs about 54 grams, you must add 54 to the BESS number you get on that device for it to be comparable to BESS scores taken on the PT50 series.

This has the unfortunate effect of making BESS comparisons among different users very unclear. For example, on the BESS Exchange forum, some people have tried to make charts describing what BESS levels are hair whittling, hair shaving, etc. and so on. (https://www.bessex.com/forum/showthread.php?tid=185) However, among the many issues of consistency here, is that there's no telling which BESS scale they're using unless they specify it. Here it does say they're using the PT50 (so it would be the BESS-C scale), but even then, there are some pretty big discrepancies between this scale and other peoples' observations. For example, my beard hair gets whittled at <=150 BESS-C (the scale the PT50 uses) or <=96 BESS-A (the original scale used by the KN100), whereas the user who put together these comparisons lists that as only achievable down at the 25-30 area. No telling what causes the discrepancy; maybe I have wire edges, maybe my hair is so coarse it just gets whittled super easy, maybe I'm making it easier by whittling towards the follicle rather than away from it, etc. *shrug* Plus you again have to consider the issue of dynamic load vs static load, and that you can get lower scores by severing the media at different rates, temperature of the media, humidity, et al.

So, unfortunately, I still don't find the BESS scale to actually be super useful for us to be able to compare sharpness results with different people; though a lot of this is due to no fault of the system, but rather just the results and tests people are comparing it to. On the other hand, as you pointed out, it's still a useful tool to make observations against your own edges and uses where you can control the factors which can lead to inconsistencies. However, as I said before, this whole system was inspired by similar fishing-line testers that were popular online years earlier, and the consistency of that media versus the BESS media apparently leaves a lot to be desired. I'm guessing you could probably spend just as much money trying to find the perfect fishing line as you'd spend just buying a spool of the BESS certified media.

You may have seen me mentioning some BESS scores testing the CPM 15V Manix 2 here: viewtopic.php?f=2&t=93878&start=100#p1681889 I adjusted all my scores to the BESS-C scale and you can also see where the numbers can get really inconsistent at times. There will be weird instances where the media won't get severed no matter how much weight gets added, or when it suddenly takes significantly more weight than previously, and then takes the normal weight again right afterward. So all of the scores I discuss are actually an average of 3 different measurements taken, usually with any outliers thrown out if they were significantly different than the rest of the set.

Anyway, I hope some of this info is helpful and I'll be curious to see your progress on your DIY version.
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Re: What exactly is a CATRA Edge Tester?

#8

Post by RustyIron »

kennbr34 wrote:
Tue Feb 07, 2023 8:53 am
So, unfortunately, I still don't find the BESS scale to actually be super useful for us to be able to compare sharpness results with different people;

Thanks for taking the time to shed a little light on the subject. I was curious about all the variables, and concluded that the human factor would always be so great as to make any data suspect.

My plan is to use fishing line for my test media. My initial fishing line experiments have given results that are completely repeatable. The fishing line, cheap scale, and my manual dexterity all give very consistent results, usually zero deviation on a scale with 1/2 gram accuracy. That's good enough for what I'm doing, but I need to do more testing to confirm repeatability.

I'm no fisherman, but I have three different spools. 50 pound is WAY too heavy. 2 pound is too light. And I have an unlabeled spool that is pretty close. My intention is to talk to fisherman friends and get a variety of fishing line to test. If I can find something that gives me results that are consistent with the published BESS charts, then I'll buy a whole spool and live happily ever after.

If you shave using Feather or Nacet blades, I'd really appreciate how they tested on your device. Did you test your Manix 2 15V as it came from the factory? I have a spare M2 15V in the drawer that I was intending to never touch, but if it's in the name of Edge Science, I suppose I'd be willing to ruin its originality.

But whether the little tool proves useful isn't all that important. I wanted to make an aluminum cylinder, cut some perpendicular slots, slice off some 45 degree surfaces, drill/tap a couple holes, and make it pretty. Even if it doesn't serve a useful purpose, it will look cool sitting on my desk.
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Re: What exactly is a CATRA Edge Tester?

#9

Post by JRinFL »

vivi made one and posted about it not too long ago. Search his posts to find the details

Yours looks professional!
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Re: What exactly is a CATRA Edge Tester?

#10

Post by kennbr34 »

RustyIron wrote:
Wed Feb 08, 2023 12:32 am

If you shave using Feather or Nacet blades, I'd really appreciate how they tested on your device. Did you test your Manix 2 15V as it came from the factory? I have a spare M2 15V in the drawer that I was intending to never touch, but if it's in the name of Edge Science, I suppose I'd be willing to ruin its originality.
Sorry, I am of no use in either instance. In regards to the razors, part of the original design means it's very limited on resolving sharpness I'm double edge razor blades because the weight is the platen alone is enough to sever the media. So all I would be able to say is whether they were under 54.

Then with the Manix 2, I re-profiled it almost immediately. However, if an anecdotal observation is adequate, I will say that it came from the factory just as sharp or sharper than what I finished it to at the start and finish of my testing, based on the 3-finger test, shaving and hair whittling ability. Not to protect my own ego, I didn't really try to get it as sharp as I could, and was just trying to match the factory edge so I wouldn't want to baby it--I never want to use an edge I get ridiculously sharp. But I think they had it a little sharper out of the factory honestly. Definitely wouldn't have touched it if I had wanted to keep the edge geometry it came with. Just based on past experience, if I really wanted to get it as sharp as I possibly could, I don't think it would have any trouble matching some of the finer-grained steels that I have gotten down to 54 BESS--which, again, is the lowest I could measure with the KN100 prototype.
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Re: What exactly is a CATRA Edge Tester?

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kennbr34 wrote:
Thu Feb 09, 2023 5:46 pm
Not to protect my own ego, I didn't really try to get it as sharp as I could, and was just trying to match the factory edge so I wouldn't want to baby it--I never want to use an edge I get ridiculously sharp. But I think they had it a little sharper out of the factory honestly.

Thanks. I read your post just minutes before I was intending to go downstairs and touch up a couple knifes that were less than perfect. That got me inspired to get out my highly scientifical kitchen scale and precision NASA approved fishing line.

When testing, I'm doing the cut freehand. In repeated tests, I'm able to get <5% variability. That's perfectly fine for me.

I only did one experiment playing with varying grits between 250 and 4k. It seems that the lower grit finishes (bigger diamonds) cut with a little less pressure. That was interesting, but I only tested this once and need to repeat it.

The three Spydies I was working on will easily shave my arm, and they're too sharp to ever get near my face. Whether it was the 15V, K390, or SPY 27, they were all cutting the fishing line within a couple percent. I suppose that shouldn't be too surprising. I'm sharpening them all the same, at about 26-30 degrees, and either 650 or 1100 grit. The readings on my contraption are about 218 to 228 grams.

There's one more kitchen knife I like. It's an old Case with some kind of carbon mystery steel. I gave it a quick 40 degrees with the brown Sharpmaker rods, and the knife would gut at about 330 grams. This edge wasn't as good as it could have been, but it was good enough.

So it seems the results of my experiments are consistent with the BESS numbers in the charts. Whether this can be useful in the day-to-day sharpening of my knives remains to be seen. But I'm learning stuff, and sometimes the joy of learning can be an end unto itself.

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Re: What exactly is a CATRA Edge Tester?

#12

Post by kennbr34 »

RustyIron wrote:
Thu Feb 09, 2023 7:44 pm
kennbr34 wrote:
Thu Feb 09, 2023 5:46 pm
Not to protect my own ego, I didn't really try to get it as sharp as I could, and was just trying to match the factory edge so I wouldn't want to baby it--I never want to use an edge I get ridiculously sharp. But I think they had it a little sharper out of the factory honestly.

Thanks. I read your post just minutes before I was intending to go downstairs and touch up a couple knifes that were less than perfect. That got me inspired to get out my highly scientifical kitchen scale and precision NASA approved fishing line.

When testing, I'm doing the cut freehand. In repeated tests, I'm able to get <5% variability. That's perfectly fine for me.

I only did one experiment playing with varying grits between 250 and 4k. It seems that the lower grit finishes (bigger diamonds) cut with a little less pressure. That was interesting, but I only tested this once and need to repeat it.

The three Spydies I was working on will easily shave my arm, and they're too sharp to ever get near my face. Whether it was the 15V, K390, or SPY 27, they were all cutting the fishing line within a couple percent. I suppose that shouldn't be too surprising. I'm sharpening them all the same, at about 26-30 degrees, and either 650 or 1100 grit. The readings on my contraption are about 218 to 228 grams.

There's one more kitchen knife I like. It's an old Case with some kind of carbon mystery steel. I gave it a quick 40 degrees with the brown Sharpmaker rods, and the knife would gut at about 330 grams. This edge wasn't as good as it could have been, but it was good enough.

One of the original observations that was made during the prototype testing for the KN100 is that people would expect a finish from a finer stone to be better at push-cutting, but when it came to coarse finishes, they were getting lower scores. The overall consensus was that this had something to do with the micro-serrations, aka the "teeth", of the coarser edge piercing and starting a cut on the test media and then the tension basically pulling it apart. So if you could imagine pulling a rubber band taught, and then poking at it with needles, it would eventually come apart even though it wasn't really "cut".

My suspicion is that your fishing line is probably a little tougher stuff, and that on the BESS media you'd probably be seeing scores of about 100 points lower, just based on my own experiences with shaving edges. If you have any DE razor blades lying around, I would use those to get a reading, and then set that as kind of your "zero" offset. So say your DE razor blade takes 110... Then I would subtract 110 from every reading you get. That way you're basically treating the DE razor blade as the pinnacle of sharp and a 0 score.
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Re: What exactly is a CATRA Edge Tester?

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Doesn't media tension have to pretty exacting for any measurements to have meaning? How is the tension set on these devices?
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Re: What exactly is a CATRA Edge Tester?

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kennbr34 wrote:
Thu Feb 09, 2023 11:06 pm
piercing and starting a cut on the test media and then the tension basically pulling it apart.

it would eventually come apart even though it wasn't really "cut".

That's exactly what I surmised. But I'm not smart enough to argue whether the rubber band was "cut" or "separated by a knife blade in a way that is not cutting." All I know is that if I'm in the kitchen and I lop off the end of an artichoke with minimal effort, then I'm happy. If someone yells, "HEY! You didn't cut that artichoke!" I'll politely ask them to GTFO of my kitchen and to slow down on the wine. Or maybe I'll pour them another glass of wine, and just keep an eye on them to make sure they don't hurt themselves with my knives.
kennbr34 wrote:
Thu Feb 09, 2023 11:06 pm
My suspicion is that your fishing line is probably a little tougher stuff, and that on the BESS media you'd probably be seeing scores of about 100 points lower,

That seems about right. I still might ask my B-I-L for a variety of fishing line to experiment with. If I can find something that gives me readings that correlate with the published chart, that would be best.

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Re: What exactly is a CATRA Edge Tester?

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Post by RustyIron »

JRinFL wrote:
Fri Feb 10, 2023 9:14 am
Doesn't media tension have to pretty exacting for any measurements to have meaning?

In any system of testing, whether it's your tape measure when you're framing your new workshop, or your photomultiplier tube when you're counting muons deep beneath the Earth's surface, there are inherent inaccuracies that need to be understood to give the measurements meaning.

There are indeed plenty of uncontrolled variables in my setup, and even in the store-bought device. My Aircraft Grade Precision Filament Tensioner is my thumb. I haven't found there to be dramatic deviation in my measurements, so I've concluded that my thumb is well calibrated.

My goal is not to create the most perfectly accurate edge tester devised by man. I looked at a commercially available product that might be priced outside the reach of the average hobbyist, and slapped a copy together in an afternoon. Anyone with a few hand tools, or even a sharp knife an a chunk of wood, can do the same. How cool would it be to make an edge tester using the edge you eventually test? The only cost outlay would be a kitchen scale and a roll of fishing line. Most of us probably already have those, so the expense would be zero.

With an afternoon of puttering and near-zero cash outlay, we could all have a better way of communicating edge sharpness. Frankly, talking about cutting paper and shaving our body parts isn't very scientific at all.

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Re: What exactly is a CATRA Edge Tester?

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Post by JRinFL »

My comment was not meant as a criticism, more to point out that uncontrolled variables can lead to data that is not meaningful. I think the tension of the thread (whatever type is selected and used for all tests) is more important than precisely which thread is used. I could be incorrect, but we’re all here to learn, right?

Could tension be tested by hanging a known weight from the thread and measuring deflection of the thread? Not everyone will have a well trained thumb that has decades of experience.
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Re: What exactly is a CATRA Edge Tester?

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Today I picked out the filament that I'll use from now on and did some testing of a few different blades.

What did I learn?
Feather and Gillette Nacet blades are close to equal in sharpness.
Finer grit stones result in sharper blades.
Stropping (1 micron diamond slurry on nanocloth) results in a sharper blade.
Stropping with 0.25 micron results in a sharper blade than stropping with 1 micron.

None of the above is a revelation, but it kept me entertained while locked inside on a cold, rainy day.
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Re: What exactly is a CATRA Edge Tester?

#18

Post by TTFulltimer »

I see a lot of people doing BESS tests on various and sundry. What is never revealed is what level of machine they are using. The Home level has very coarse resolution, within 25 grams. So that 125 reading might be 100 or 150. And it is not repeatable. The next level of the tester the Professional has a resolution of 5 grams and then that 125 reading might be 120 or 130. The best machine is the Industrial with a 1 gram resolution so a 125 reading might be 123 or 126. And as one might expect the prices are reflective of that degree of resolution. About 125, 170, and 242 USD.

Most of the so called testing that you can find are more like experiments. If instrumentation is used is it calibrated? Has anyone done experimental analysis to see what the actual range of their measurements might be? Or are they just getting "Meaments"? Those are measurements with the "Sure" taken out.
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