EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES

EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - Printable Version

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EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - KnifeGrinders - 05-02-2018

Edge Stability in Butcher’s and Kitchen Knives as a Function of Edge Angle and Initial Sharpness

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Structural Edge Tester (SET) is a method and device developed by Edge On Up for testing edge stability. In a nutshell, the edge is subjected to controlled rolling, the extent of which is quantified.
Edge sharpness tester used in the study: PT50A Industrial.
Laser protractor: CATRA HobbiGoni Knife-Edge Protractor.

[Image: SET_tester.JPG]

Impact cycle explained

The impact roller is a linear bearing slant at 10° to the horizontal base or in other words at 80° to the plane of the blade clamped vertically.
Standard impact assembly weight is 150 grams.

[Image: SET_testing10.JPG]

The impact roller is lowered at "A", then moved (rolled) over to "B" and then back to "A".
A-B-A is one cycle.

[Image: SET_Cycle.png]

See our Video on YouTube >>

PLAN

The plan is to use SET to test edge retention in butcher’s and mainstream kitchen knives sharpened in the "very sharp" range of 50 BESS, 100 BESS, 150 BESS and 200 BESS for edge angles 8, 10, 12, 15 and 20 degrees per side.

The initial sharpness of 50 and 100 BESS represents the sharpest edges nearing a DE razor, while the initial sharpness of 150 and 200 BESS – just sharp knives in the range of utility blade sharpness.

Edge angles of 8 and 10 degrees per side (dps) are more typical of high carbon Japanese knives, while edge angles of 15 and 20 degrees are common in Europe (30° included) and the USA (40° included).
Mainstream kitchen knives are commonly produced with the edge angle of 30° included.
Meat processing plants usually sharpen their knives at 35-40° included.

These edge angles have become common through the sharpening tradition, and our research is to validate the tradition or challenge it.

Another aspect of our study is to see whether there is any relation between the initial knife sharpness and edge retention. Traditionalists say that to hold the edge well the knife should be just working sharp, while enthusiasts say “the sharper the better”; this is the least researched area.

KNIVES

We started the testing with Victorinox/Wenger SWIBO professional meat processing knives of HRC 56-58 and Carbon content 0.5%, new out of the box.

To minimise change in the blade profile due to repeated sharpening, for each edge angle we used a separate new knife; all knives are identical, Victorinox Catalogue # 5.8401.14

[Image: SWIBO_58401_14.png]

Though steel of these knives best matches Victorinox kitchen knives X50CrMoV15, they can represent butcher’s and mainstream kitchen knives of other brands as well.

SHARPENING METHOD

Edge angle was ground on Tormek T-8 with the help of our computer software for Tormek, and verified with a CATRA laser protractor in each case.

[Image: Laser_Protractor.JPG]

Sampled knife edge is 15 dps (30 degrees included)

CBN wheels 254mm in diameter were used: edge bevels were ground on CBN grit #400, and the edge set on CBN grit #1000.
The CBN wheel was chosen over the Tormek or Japanese wheels for the precision it offers, as the CBN wheel diameter never changes, while the stone wheel diameter drops with grinding due to the consumption of the abrasive, slightly increasing the grinding angle in the process.

The target edge sharpness was set by controlled-angle honing on paper wheels with a fine diamond paste within +/- 10 BESS of the target.
The honing angle was controlled with the help of our software for paper wheels.

[Image: test_knives.JPG]

DATA
Data numbers in the charts is the number of the impact roller cycles with the resultant sharpness.
E.g. “ x1 = 150, x2 = 300 “ means after 1 impact cycle the edge sharpness is 150 BESS, after 2 cycles 300 BESS, and so on.

For the purpose of this study, we measured the edge sharpness after every cycle for the first 5 cycles (Phase I), then after every 5 cycles to 50 cycles (Phase II), and then (i.e. from the 50th to 100th cycles) after every 10 cycles (Phase III).

This way we’ve covered the two checks that have been agreed as checkpoints for all field testers:
sharpness value after 5 cycles - Phase I checkpoint for “elastic deformation”; and
number of cycles causing "permanent rolling" - Phase II checkpoint for “plastic deformation”.

VICTORINOX/WENGER SWIBO BUTCHER’S KNIVES
Stainless steel, Hardness HRC 56-58, Carbon 0.5%

Link to raw SET data >>
Graphs I build on those numbers later on are a tad more comprehensible.

An 8 dps edge (16 ° included) collapses on the test line – see the microscope image.

[Image: SWIBO_8_degrees.jpg]

I had to estimate sharpness by alternative methods described in our Sharpness Chart:
Around 50 BESS – splits a hair but won’t cross push-cut Tally-Ho cigarette rolling paper;
Around 100 BESS – won’t split or cut a hanging hair, but longitudinally push-cuts Tally-Ho cigarette rolling paper and violin hair sign is positive;
Around 150 BESS – won’t longitudinally push-cut Tally-Ho cigarette rolling paper and the violin hair sign is negative, but shaves forearm;
Around 200 BESS – won’t shave forearm, though force-scrapes off the hair, and slices a sales docket.

[Image: cig_paper_swibo.JPG]

While measuring the 8dps blades on the Edge Sharpness Tester, the test line dents edges sharpened to 50, 100, 150 and 200 BESS, rendering further SET tests both impossible and meaningless.
Just for the protocol, the score in the dents is 800-1500 BESS.

A 10dps edge (20 ° included) is also dented by the test line, though to a lesser degree than the 8dps, so that the dents can barely be seen naked-eyed but nevertheless rendering further SET tests meaningless for practical purposes – the next microscope image shows 2 dents left by attempts to measure sharpness of an 80-100 BESS edge, followed by an image of a shallow dent left by the test line on a 10dps edge sharpened to 180-200 BESS.

[Image: SWIBO_10_degrees_100BESS.jpg]

The score in the dents is within 200-600 BESS, which we interpreted as promising of a better edge stability in edges sharpened at a higher angle, and further experiments proved this.

12 dps edge (24 ° included) is stable
The following microscope image shows the 12dps edge of initial sharpness 50 BESS after 20 SET measurements taken at the same spot – the black mark is where the sharpness was repeatedly measured, and as you see this point is undistinguishable from the rest of the edge.

[Image: SWIBO_12_degrees.jpg]

To make sure the test line itself does not effect the edge as it was the case of 8dps and 10dps edges, after 100 impact cycles we took an additional sharpness measurement a few mm away from the mark, on an edge segment that had not been measured for sharpness but was still in the impact area, and the sharpness score was virtually the same as in the point used for measurements.

At 12 dps knife edge response to the test load remotely resembles that of a slow wear, whereas at 10dps and lower it is an immediate deformation.
I say “remotely resembles” because a rolled edge and edge blunted by abrasive wear behave differently: the bent springy edge shows fluctuating sharpness scores up and down as the edge deteriorates, while abrasive wear shows more linear blunting.

EDGE RETENTION

The following graphs show edge retention as a function of initial sharpness.

12 dps (24° included)

Initial Sharpness - Average Sharpness Score over 100 Cycles
50 BESS - 368
100 BESS - 399
150 BESS - 425
200 BESS – 435
The sharper is the edge the better is retention.

[Image: chart12dps.png]

15 dps (30° included)
Initial Sharpness - Average Sharpness Score over 100 Cycles
50 BESS - 411
100 BESS - 438
150 BESS - 465
200 BESS – 494
The sharper is the edge the better is retention.

[Image: chart15dps.png]

500 BESS is where the knife turns blunt.
At 15 dps, knives sharpened under 100 BESS (i.e. near razor sharp) stay sharp twice as long as knives with the initial sharpness of 150-200 BESS (i.e. utility blade sharpness) – 80 impact cycles vs 40.

20 dps (40° included)
Initial Sharpness - Average Sharpness Score over 100 Cycles
100 BESS - 455
150 BESS - 541
200 BESS - 545
The sharper is the edge the better is retention.

[Image: chart20dps.png]

500 BESS is where the knife turns blunt.
At 20 dps, knives sharpened to 100 BESS (i.e. next to razor sharp) stay sharp twice as long as knives with the initial sharpness of 150-200 BESS (i.e. utility blade sharpness) – 40 impact cycles vs 20.

***
By the far-famous Cliff Stamp’s concept and his experimental data, an edge of 12 dps should outperform those of 15 and 20 dps. Cliff Stamp advocates that knives should have the thinnest edge possible for a given blade steel and task.
If our SET tester data are in line with Cliff Stamp’s concept it would prove the SET can be an alternative to cutting tests that Cliff used to prove his concept.

To see what our SET tester shows in this regard, we’ve averaged sharpness data across all initial sharpness for each edge angle– this way we abstract from the initial sharpness and focus on the edge angle.
For example, average sharpness after 10 Cycles was calculated for 12 degree edge as: (338 + 385 + 384 + 419)/4, where 338 is the score for the initial sharpness of 50 BESS, 385 is the score for the initial sharpness of 100 BESS, 384 is the score for the initial sharpness of 150 BESS, and 419 is the score for the initial sharpness of 200 BESS.
Averaging this way not only better reveals the tendency, but also increases trust in the data we’ve obtained, because the sets of data for each initial sharpness can be treated as a retention test repeated on 4 different knives to confirm reproducibility of the results; in confronting reality people cut with varying initial sharpness.

Link to averaged SET data >>

The following chart and graph show edge retention as a function of edge angle.

EDGE ANGLE – AVERAGE SHARPNESS
12 dps (24 ° included) - 407
15 dps (30 ° included) - 452
20 dps (40 ° included) - 514

[Image: chart_retention.png]

These averaged data tell us the best retention has the edge sharpened at 12 dps, and we already know that at this edge angle the best performing is the initial sharpness of 50 BESS i.e. razor sharp.
Knives sharpened at 20 dps turn blunt (500 BESS) by the 20th impact cycle, knives at 15 dps outlast twice as long, and knives at 12 dps over 3 times longer.
The edge angle has clearly a more definitive effect on the knife performance than the initial edge sharpness, unless this sharpness is <= 100 BESS.

Our SET data are in line with Cliff Stamp’s cutting tests and concept.

COMPARISON TO EDGE RETENTION AT A MEAT PLANT

[Image: meat_plant.jpg]

SWIBO knives similar to those used in this research were used in a separate research on edge retention at a meat plant.
Overall 8 boning operators used four SWIBO knives for two days: 4 operators on the day 1, and another 4 on the day 2; the edge sharpness was measured every 1.5 hours throughout the work shifts.
These knives were sharpened at 40 degrees with the initial sharpness about 100 BESS.
The meat plant averaged data are shown below

Sharpness through the work shift (BESS)
Initial sharpness - 115 BESS
In 1.5 hours - 308 BESS
In 3 hours - 316 BESS
In 4.5 hours - 324 BESS

Compared to the knives sharpened at 40 degrees with the initial sharpness of 100 BESS in our SET research the meat plant edge retention numbers fall within the range of the first 5 impact cycles.

CONCLUSIONS

The testing regimen had been designed right, because sharpness of all knives neared or exceeded 500 BESS i.e was rendered blunt by the 100th impact cycle.

The SET method has proved a valid and better alternative to cutting tests for edge retention, providing the researcher with precise data suitable for quantitative and statistical analysis.

“The sharper is the edge the better is retention” appears to be a rule for all edge angles.

The optimal edge angle for butcher’s and mainstream kitchen knives is 12 dps (24 ° included), sharpened to 50-100 BESS (i.e. nearing a DE razor in sharpness), though the edge angle is clearly a stronger determinant in the edge retention compared to the initial sharpness.
At this angle the edge and apex are both strong enough to resist deformation.
Knives sharpened at 12 dps stay sharp 3 times longer than knives sharpened at 20 dps, and almost twice as long as 15 dps knives.
On the contrary, lower than 12 dps edges are too weak and easily deform under the load.

As it has been mentioned, SWIBO knives steel best matches Victorinox kitchen knives X50CrMoV15 (HRC 56-58, Carbon contents 0.5%).
For higher end kitchen knives (e.g. Global HRC 56-58 Carbon 0.7%) we expect the optimal edge angle to be under XX dps, while for those with Carbon contents <= 0.45% (e.g. Scanpan x45CrMoV15 HRC 56-57 Carbon 0.45%) to be higher. These two lines of knives are being tested as I type this.

We’ve proved that the SET method can be used to determine the most robust edge angle for knives used at meat processing plants.
Sharpening at the best angle for a given knife brand ensures the best edge retention, sharpness and longer life span of the knives, saving plants tens of thousands of dollars a year.
We think of slightly lessening the impact to better match the SET to the meat plant numbers obtained in live studies; we should be able to do this by lessening the angle at which the impact roller meets the edge; additional tests are required to determine the right roller angle.
You may call us day dreamers, but we hope to equal one impact cycle to one hour of cutting at the meat plant conveyer.

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CONTINUED BELOW IN THIS THREAD...

RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - Bud - 05-02-2018

Good gosh Mr. Knifegrinders this is an amazing report! It's too late at night to understand all of it but I'll be back on it over my lunch break tomorrow. Thanks so much! This is a lot of effort and am very thankful for your good work. Hopefully, more tomorrow from me.

RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - Jan - 05-03-2018

Knife Grinders, thanks for posting your very interesting edge stability study! Thanks for preparing the PDF version of your study also.

Your paper accompanied with measured data charts and suitable graphs is an excellent material uniquely supporting your conclusions.

Your paper is the best promoting material for SET I can imagine. Smile

Congrats!
Jan

RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - EOU - 05-03-2018

We agree with Bud KG. Your tests are amazingly well conducted and documented. The comparison to actual use in the meat processing plant was just icing on the cake. We find that your discovery of "denting" caused by test media in edges sharpened at <12° to be very interesting. We've only seen it once, with a 304 stainless medical instrument and heard of it another time, in a wire edge experiment conducted by a customer in Denmark. You'd think that a well formed steel edge would hold out against a polymer based test media in all cases but that is obviously not the case here. Good fodder for future experiments.

The purpose here is to discover ways that arm sharpened edge users with information that leads to edges that stay sharper longer. You've already made a leap forward in your thinking KG in beginning to equate SET cycles to actual usage. We imagine that could be easily expanded to exploring different piston weights as well. This is going to be an important future step with the SET device as it relates to various applications. For example, had to interrupt this composition while I spoke on the phone to a new customer who manufactures power floor scrapers. His area of interest is not in 150 BESS and 12° edges but rather something much different. With regard to your meat cutting customers, I would imagine that the data you have already collected hits them right in the mid-section. So that sort of exhibits the breadth of information that must be accumulated.

Wonderful job KG. This sort of research didn't wrap-up in 30 minutes so we are very much indebted to you for your time and work.

RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - KnifeGrinders - 05-04-2018

The amount and value of data this research has yielded overachieved my expectations, as initially I only intended to prove the concept of the SET method.

Look how much interest rope cutting tests get, and think how often the conclusions drawn from these tests are contested.
Mark (R. Precision) combines rope cutting with a BESS sharpness tester to speed up his testing.
SET takes it further to the next level, closer to the CATRA cutting performance testers, but unlike CATRA's the SET device won't cost $100,000 that even large manufacturers prefer to rent from CATRA rather than buy.

Having an affordable device at our disposal that gives us numeric data quicker than cutting tests and of better quality, will have many questions answered.

RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - EOU - 05-04-2018

Thank you for the work expended and your thoughts KG. Hopefully the results of the SET testers and our work will result in better and longer lasting edges. How about a 1/2 price sale KG? $50,000.00 and a SET could adorn everyone's work bench.

RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - KnifeGrinders - 05-07-2018

SEQUENCE #2
Using the same methods and equipment, we tested edge retention in two more brands of kitchen knives: one of less hardness, less Carbon contents and known to hold the edge worse than the Victorinox SWIBO knives, and the other of higher Carbon contents and known to hold the edge better.
The only difference with the previous tests was that to study relation between the initial sharpness and edge retention we used the initial sharpness of 100 BESS (i.e. next to razor sharp) versus 200 BESS (i.e. utility blade sharpness).

STEP DOWN
SCANPAN Classic Kitchen knife
Stainless steel X45CrMoV15, Hardness HRC 56-57, Carbon 0.45%

[Image: Scanpan.JPG]

Link to SCANPAN Data >>
We average data the same way we did for the SWIBO knives, mainly to boost trust in the data we’ve obtained, because the sets of data for each initial sharpness can be treated as a retention test for a given edge angle repeated on different knives to confirm reproducibility of the results.

10 dps (20° degrees included) edge
A shaving sharp 10 dps edge about 150 BESS by the Sharpness Chart, is dented by the test media line, scoring in the dent 700 BESS on the sharpness tester.

As it was in the case of Victorinox SWIBO knives, this indicates the angle at which the edge becomes unstable and easily deformable, rendering further tests both meaningless and impossible.

[Image: SCANPAN_10dps.jpg]

12 dps (24° degrees included) edge
Microscopy is unremarkable – no visible deformation after sharpness measurements.

***

The following charts show edge retention as a function of initial sharpness.

12 dps (24° included)

Initial Sharpness - Average Sharpness Score over 100 Cycles
100 BESS - 485
200 BESS - 632
The sharper is the edge the better is retention.

15 dps (30° included)

Initial Sharpness - Average Sharpness Score over 100 Cycles
100 BESS - 631
200 BESS - 611
No relation between the initial sharpness and edge retention (difference < 5%).

20 dps (40° included)

Initial Sharpness - Average Sharpness Score over 100 Cycles
100 BESS - 650
200 BESS - 624
No relation between the initial sharpness and edge retention (difference < 5%).

***

The following chart of averaged data shows edge retention as a function of edge angle.
EDGE ANGLE (dps) 12° - 15° - 20°
AVERAGE SHARPNESS 559 - 621 - 637

The thinner is the edge the better is retention.

************************************************************************

STEP UP
GLOBAL Classic Kitchen Knife
Stainless steel CROMOVA 18, Hardness HRC 56-58, Carbon 0.7% (other source 0.55%)

[Image: Global.jpg]

Link to GLOBAL Data >>

8 dps (16° degrees included) edge
An 8 dps edge under 100 BESS by the Sharpness Chart, is dented by the test media line, scoring in the dent 300-500 BESS on the sharpness tester.
I am aware that this contradicts common opinion that Global knives can be sharpened to 15 degrees included, yet at this angle the edge is too weak in the apex for testing by our methods.
Below are microscope images of several attempts to measure sharpness on the BESS tester.

[Image: Global_8dps-1.jpg]

10 dps (20° degrees included) edge
Microscopy is unremarkable – no visible deformation after sharpness measurements.

***

The following charts show edge retention as a function of initial sharpness.

10 dps (20° included)

Initial Sharpness - Average Sharpness Score over 100 Cycles
100 BESS - 429
200 BESS - 454
The sharper is the edge the better is retention.

12 dps (24° included)

Initial Sharpness - Average Sharpness Score over 100 Cycles
100 BESS - 475
200 BESS - 437
Reverse relation between the initial sharpness and edge retention.

15 dps (30° included)

Initial Sharpness - Average Sharpness Score over 100 Cycles
100 BESS - 473
200 BESS - 540
The sharper is the edge the better is retention.

20 dps (40° included)

Initial Sharpness - Average Sharpness Score over 100 Cycles
100 BESS - 509
200 BESS - 500
No relation between the initial sharpness and edge retention (difference < 5%).

***

The following chart of averaged data shows edge retention as a function of edge angle.

EDGE ANGLE (dps) 10° - 12° - 15° - 20°
AVERAGE SHARPNESS 441 - 456 - 507 - 504

The thinner is the edge the better is retention.

STEEL COMPARISON

The following charts and graphs compare the knives edge retention.

The following two charts show edge retention by steel, and include average sharpness and number of impact cycles it took to render the edge blunt i.e. over 500 BESS (a key indicator).

[Image: comparison2.png]

The following graph shows the best edge retention by averaged data for each of the steels tested; additionally shown is one more GLOBAL sharpened at 30 degrees included.

[Image: graph_comparison.png]

The lower ranking SCANPAN at 12 dps outperforming GLOBAL at 15 dps (though not for long) can be explained by the advantage of the lower edge angle, but what about the winning SWIBO?
The seemingly paradoxical SWIBO knives outperforming the higher ranked Global is discussed in the Conclusions below.

CONCLUSIONS

Softer steel (Step down)
The optimal edge angle for mainstream kitchen knives with HRC 56-57 and Carbon 0.45% is 12 dps (24° included), sharpened to 100 BESS; the 12 dps edges with the initial sharpness of 100 BESS stay sharp twice longer compared to the initial sharpness of 200 BESS.
Edges sharpened at 12 dps stay sharp twice as long as those sharpened at 15 and 20 dps, and the 15 dps edges hold sharpness somewhat better than 20 dps - the edge angle remains a strong determinant in the edge retention of softer steel.
Lower than 12 dps edges are too weak in the apex.

Compared to the SWIBO knives, the SET load causes early plastic deformation in the edge of the softer steel X45CrMoV15.

Absence of relation between the initial sharpness and edge retention that we see in easily deformed edges sharpened at 15 and 20 dps, suggests that the initial sharpness helps to hold edge only in the elastic deformation phase.

Harder steel (Step up)
The optimal edge angle for better kitchen knives like Global is 10 dps, sharpened to 100 BESS; the 10 dps edge stays sharp by 50% longer than the 12 dps edge, and over 2 times longer than the 15 dps edge.

Edge retention as a function of edge angle

Best edge angle for a knife is the lowest angle at which the edge can take a load without deforming.
Steels have a certain smallest angle at which the edge becomes unstable, the stronger the steel the smaller is this angle.

Edge retention as a function of initial sharpness

Generally, the sharper edge shows better retention.
Edge retention is improved by the initial sharpness under 100 BESS, however this relation becomes less consistent at and over 100 BESS, especially in lower ranking steels.

Comparison by steel

A knife made of weaker steel, but sharpened to its best at the acutest angle it can hold may outperform a knife of stronger steel sharpened at a more obtuse angle.

As seen by the test data, even a lower ranking SCANPAN knife sharpened to 100 BESS at 12 dps outperforms GLOBAL knife sharpened to 200 BESS at 15 dps.

The above is the common rule ensuing from our SET testing, but not without many exceptions, and when the exceptions are abundant, this usually tells us there is another hidden rule behind them we are yet to comprehend.

The main paradox we see is that SWIBO knives outperform the more wear-resistant Global in our tests.
Obviously, edge rolling is far not the same as wear resistance, and a mainstream steel like SWIBO can tolerate rolling better than a harder steel like GLOBAL; steel compressive strength seems to retain the edge within the elastic deformation range better than hardness.

SET testing method

Number of cycles had been guessed right because sharpness of all knives neared or exceeded 500 BESS (i.e was rendered blunt) by the 100th impact cycle – allowing us to watch the full life cycle of the edge within one test.

The testing procedure yields additional information about events happening in the edge as reflected by the test data. The testing regimen we’ve applied in these series of SET testing has 3 distinctive phases:

·        Phase I “Elastic deformation” from the 1st to the 5th impact cycle, when sharpness is measured after every cycle – considering that interval between subsequent impact cycles is about 30 sec, this break in impact allows the edge to partially recover from rolling. This phase takes about 2.5 min.

·        Phase II “Elasto-Plastic transition” from the 6th to 50th impact cycle, where the edge gets 5 impact cycles between sharpness measurements – edge is challenged for resistance to plastic deformation. The elastic deformation transits to plastic here, as seen by the lessening of variances in sharpness in the second half of this phase. Phase II is where the initial sharpness contributes the most to the edge longevity through the enhanced elasticity of the thinned edge. Weaker steel simply crashes in this phase. This phase takes 5 min.

·        Phase III “Plastic deformation” from the 51st to 100th impact cycle, where the edge is continuously rolled 10 times before each next sharpness measurement, testing the edge stability to permanent rolling. This phase takes about 3.5 min.

Key indicators:
- Overall average sharpness over 100 impact cycles;
- Average sharpness in the Phase I (elastic deformation) - calculated as an average sharpness scores in the first 5 impact cycles;
- Sharpness by the end of the Phase II (elasto-plastic transition) – calculated as an average of 3 sharpness scores: after 40, 45 and 50 impact cycles;
- Number of impact cycles to turn the edge blunt at 500 BESS (resistance to permanent rolling).

Overall, each SET test takes 11 minutes to estimate life cycle of the edge; for comparison, CATRA’s “knife sharpness and life tester” takes 15 minutes in the semi-automatic model and 10 minutes in the automatic model.

SET and CATRA testing should not be opposed, as they focus on different attributes of the edge:
of the two main constituents of the edge blunting, SET testing focuses on the edge rolling, while CATRA on the abrasive wear; of the three main steel properties playing role in the edge retention: strength, toughness and hardness - strength is more about resilience to rolling, while hardness to wear.
More tests are needed to estimate edge rolling in so called “super-steels”, and compare to the mainstream steels; the data we’ve got so far tell us that the “super-steels” are not necessarily superior in resilience to rolling unless compared to lower end steels.
Lately we and EOU have been getting more experimental facts that wear resistance and edge resilience to rolling may be unrelated.

The SET method has proved to distinguish different types of steels, even when this difference is subtle, just when interpreting SET data keep in mind that in SET compressive strength/elasticity wins over hardness, as it often does in the kitchen.

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RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - Mark Reich - 05-08-2018

Wow! Truly an incredible amount of data, Vadim! My hat is off to you, Sir!

RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - grepper - 05-08-2018

Mr. KG, that is an amazing and well documented bit of research. Thanks for the incredible effort and for sharing the results. Very interesting stuff.

There is one thing I’m unclear about and wonder if you can assist me in understanding what’s going on. You present images of blades at 100 and ~150 BESS with “dents” in the edge and state that the dents were caused by the test media. That would indicate that those blades can’t cut through a piece of thin plastic line .009” diameter with only 100-150g force without damaging the edge?

Razor blades @ 50 BESS don’t dent, and Feather blades @ 35 don’t dent. I don’t understand how a 100-150 steel edge can be dented by a thin little piece of plastic line. If those blades can be dented by a little piece of plastic test media with only 100-150gf, it would seem like cutting something like a carrot let alone impacting a bone would totally ruin the edge.

I have however observed burr being dented by test media. Looking very carefully at the images you posted, I think I can see burr. It’s difficult to tell due to the lighting in the images, but there seems to be some reflection at the edges of the blades. Could this possibly explain what’s going on?

Here is an example image I took of burr dented by test media:

[attachment=647]

RE: EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES - KnifeGrinders - 05-08-2018

I don't see why it should be surprising at all. Every steel has an edge angle so thin at the apex that it crashes or bends under the load.
Apex denting by the test media line is a fact having nothing to do with the burr or my sharpening method. My deburring was the same in all knives.
Take Global - dented at 8 dps, but not 10 dps; take SWIBO - dented at 8 and 10 dps, but not 12 etc - if it were because of a burr, it would just keep denting.
The apex at 8 dps would not dent if rather than cross push-cut we slice the test line at an angle.
Your example of "Razor blades @ 50 BESS don’t dent" is not right - you do not get a visible dent, but the score worsening in subsequent sharpness tests tells us that the blade apex gets rolled under the test line.

We applaud Mike's new invention and the EOU team for this wonderful device - never before have I had such a deep insight into the knife edges in so little time as with the SET.
Though maybe it is not too late to rename it to ERT for Edge Rolling Tester to accent what it actually does.