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Blade Sharpness Research Project

1000006313.jpg


Here are some preliminary measurements with my new PT50A scale:

6/2/24


DevicePT50APT50APT50APT50A
MediumBessBessTrilene XL 6Trilene XL 6
Astre SP Russia10101010
Top47544359

56747874

61596052

83874571

59436348
Bottom73584780

76523170

77544774

48654145

43715536

I am pleased with how consistent the first two sets are; means within 1%. I am not so pleased that my fishing line wasn't nearly as consistent. This isn't enough data to draw any conclusions.

Probably best to try this with a new and highly regarded blade, that is more likely to have consistent sharpness across its length. Another India Astra SP will probably be suitable. And of course, lots of data points.

I will probably wait for my bread lames and shavettes to come. I think I can use them with the fulcrum that came with this, to reduce slicing, and the shavettes should also get rid of flexing and bending.

Meanwhile, I will shave ten times with another blade to get some more information about blade wear. As I develop a process for artificailly wearing blades, I think it will be useful to have some different naturally worn blades around.
 
I’m excited to see how this goes. It would be nice if you could test out some popular/common new blades without shaves instead of having to wait a couple weeks for each test. Just for curiosity sakes. And continue to do the 10 shaves per blade separately.

On the subject of corking, I didn’t have a cork but wanted to try this so I bunch up toilet paper/tissue paper and run each edge through the soft paper 3 times without much pressure. I imagine it’s slightly less aggressive then a cork. Usually 2 squares of toilet paper bunched up in a ball works great.

I don’t do this for every blade because some blades like the GSB or Russian Astra SP are so smooth they don’t benefit from it. But 2 of my other favorites the Rubie and Nacet do benefit from this. Usually the first half of the first pass would feel a little rough if I didn’t “cork” the blade but would smooth out very quickly. So it’s not a big deal if I don’t cork them but I prefer to have my full shave be buttery smooth so the added 10 seconds of corking makes it worthwhile for me.
 
I've seen a description of how some manufacturers test their DE blades for quality control during production.

The tests were done by cutting through stacks of paper with a fixed amount of force applied to the blade holder. The sharpness measurement was based on the depth of the cut that was made through the stack of paper using the fixed amount of force.

Just thought that might be of interest.
 
I’m excited to see how this goes. It would be nice if you could test out some popular/common new blades without shaves instead of having to wait a couple weeks for each test. Just for curiosity sakes. And continue to do the 10 shaves per blade separately.
That is the plan. I am only going to use the 10 shave blades as a baseline for whatever artificial dulling process I settle on. A good consistent artificial wear process should be superior to natural wear for comparability anyway. I don't want to space the blades out 10 days either. I want to be able to sit down for an hour or two and get a full set of measurements and objective analysis.

There is already a plethora of subjective stuff published here, on wicked edge, and other places. I do eventually want to put some of my own notes up, but it is lower importance and lower urgency than the measurements.

I should have some shavettes and bread lames here soon, and then I can hammer out the kinks with a good measurement process and really get rolling.
 
I've seen a description of how some manufacturers test their DE blades for quality control during production.

The tests were done by cutting through stacks of paper with a fixed amount of force applied to the blade holder. The sharpness measurement was based on the depth of the cut that was made through the stack of paper using the fixed amount of force.

Just thought that might be of interest.
This is the first thing I will try for artificial dulling. I already have a paper slicer to make the strips.
 
I would be interested in seeing an identical test but done on blades that have been used for one shave already.
I definitely want to have an artificial wear and testing process that correlates reasonably to shaves so we can see where the blade sharpness peaks, and where it has declined significantly beyond initial sharpness.

I want to dull it enough that the change is measurable within the tolerance of my measurement process as well, so I am not showing a bunch of noise in the information at analysis.

I will see what I can come up with.

Some double edge shavettes arrived here today, so I can see how they perform on the fixture this weekend.
 
I definitely want to have an artificial wear and testing process that correlates reasonably to shaves so we can see where the blade sharpness peaks, and where it has declined significantly beyond initial sharpness.

I want to dull it enough that the change is measurable within the tolerance of my measurement process as well, so I am not showing a bunch of noise in the information at analysis.

I will see what I can come up with.

Some double edge shavettes arrived here today, so I can see how they perform on the fixture this weekend.
I'll be very interested in your results. I swear some blades get sharper after one use ...part of the coating is worn off, or something.
 
I received the shavettes, including one that works very well on the fulcrum for the test fixture.

1000006475.jpg

1000006477.jpg
I have several monofilament materials to test. I got some 8 and 10 pound test line to try. I just want to see if something works really well before I start taking a bunch of blade measurements I want to be able to compare.

1000006478.jpg


We should get there soon. I had a long driving session at the racetrack this afternoon, so that's all for today.
 
I tested various media and found the Stren 8lb 0.27mm to be the best performing. The median cutting force was essentially the same as the BESS certified test media, and the standard deviation of the cutting force was lower.

1000006537.jpg



Date6/7/246/8/246/8/246/8/246/8/24
BladeAstra SP India (0)Astra SP India (0)Astra SP India (0)Astra SP India (0)
Astra SP India (0)
LocationBottom CenterBottom CenterTop CenterTop CenterTop Center
MediumTrilene XL 6lbStren 8Force 6BessCajun 10
147845383115
245714983135
348724275114
439784889104
54376367699
649714379122
737834488133
842875778109
951723884106
1044733596106
1139784677119
1248784681134
1337784473126
1444784574127
1540755670124
1637794785112
1743785273105
1842795578113
1949697173136
2041924174113
2145806588118
2248866178103
2347866276136
2446793889126
2549784964115
2652775169144
2742755484121
2849725488117
2948845067129
3044738874146
3149738182125
3245765174128
3352836692122
3441836476116
3559804480105
3643744767139
3748696264104
3849816396116
3945796375124
4049714988130
4144806969103
4245784581102
4347766470123
4439815675148
4546906186122
4647664667128
4750744967121
4847785888122
4950744465112
5045685666123
Std. Dev.4.405.5910.988.4712.11
Mean45.577.553.1677.88120.4

If there aren't any really compelling objections, I will stick with the Stren 8-lb mono-filament as my standard test media in the foreseeable future.
 
I measured a used Astra SP Russia (10) blade, and a new one, and found about a 10% increase in cutting force after 10 shaves. The used blade is the one I measured daily in the old fixture, and those measurements indicated it probably didn't reach peak sharpness for a few shaves, due to coating wear.

I cut some 1 inch strips of standard office paper and used the new blade to slice 100 strips. Surprisingly, each sheet of paper was somewhere in the ballpark of dulling the blade as much as a daily double edged shave.

Date6/9/246/9/246/9/24
BladeAstra SP Russ (0)Astra SP Russ (10)Astra SP Russ (P100)
LocationBottom CenterBottom CenterBottom Center
MediumStren 8Stren 8Stren 8
16648174
27458137
38167166
46858175
55964153
67066158
76670169
85872234
96664148
106675231
115869146
127884165
1365101164
147274147
157582174
166061167
175965144
187161185
195468182
205870177
215174157
2254108143
235767165
246465167
256355148
265581144
275970168
288161144
297051150
306965165
316862161
327181182
337191242
347664190
358868172
367368165
376077161
386368208
395180176
405779178
418373169
426266151
436674161
446175176
456680181
465784150
476287158
486766166
496569143
506775156
Std. Dev.81122
Mean6671168

The next step is to design and test a dulling and measuring procedure. I think it might be nice to capture coating wear and approximate peak sharpness. I am considering 3 to 5 strips of paper as a test interval; perhaps measuring at 0, P5, P10, and P15, or something like that.

For the artificial wearing test above, I started with 40 sheets of paper, cut it twice, then 10, then 5 twice. The paper stack being taller than the exposed blade made clearing cut strips a problem. There is also the issue of the blade hitting the cutting board. For the standardized test, I may use and anvil of slightly more than an inch covered in rubber or something similar, but I will probably try a scrap of cherry wood first. Microscopic inspection at 120x with my Carson microscope of the heavily worn edge doesn't show any chips or other severe irregularities at the apex, so this seems to be a suitable method.
 
Looks like 0, P5, P10 is a bigger increment than I want.

Date6/9/246/9/246/9/246/9/246/9/24
BladeAstra SP Russ (0)Astra SP Russ (10)Astra SP Russ (P100)Astra SP Russ (P5)Astra SP Russ (P10)
LocationBottom CenterBottom CenterBottom CenterTop CenterTop Center
MediumStren 8Stren 8Stren 8Stren 8Stren 8
Measurements5050505050
Std. Dev.811221111
Mean66711687288
Median66691657190.5

I will try something else when I have some more time. Perhaps 0, P2, P4, P6, or something like that. Once I do that, I am going to consider reducing the number of measurements so it doesn't take an hour or more to measure and wear a blade. I think 30 data points per interval would be fine, and I might get away with 20.
 
Last edited:
I took a lot of measurements (490) tonight and learned some things along the way. I was having some issues cutting the paper in a manner that caused consistent wear, ruining a few edges along the way. I ended up with a method where I staple stacks of paper strips together, and gently push the blade in shavette through the stapled stack of paper strips into a rubber cutting board. I have to be careful to hold the shavette just right so it doesn't slice or wiggle and just pushes through.

DateBladeLocationMediumDulling SubstrateMeasurementsStd. Dev.MeanMedian
6/13/24Astra SP India (0)Bottom CenterStren 8New5076260.5
6/13/24Astra SP India (P2)Bottom CenterStren 8Paper on Rubber50116764.5
6/13/24Astra SP India (P4)Bottom CenterStren 8Paper on Rubber50106969
6/13/24Astra SP India (P6)Top CenterStren 8Paper on Rubber2029107102.5
6/13/24Astra SP Russ (0)Bottom CenterStren 8New2066563.5
6/13/24Astra SP Russ (P10)Bottom CenterStren 8Stapled Ppr Rubr20158182
6/13/24Astra SP Russ (P20)Bottom CenterStren 8Stapled Ppr Rubr20179795
6/13/24Astra SP Russ (P30)Bottom CenterStren 8Stapled Ppr Rubr2018107104.5
6/13/24Astra SP Russ (P40)Bottom CenterStren 8Stapled Ppr Rubr2015118112.5
6/13/24Astra SP Russ (0)Top CenterStren 8New2096565
6/13/24Astra SP Russ (P4)Top CenterStren 8Stapled Ppr Rubr2056566
6/13/24Astra SP Russ (P4)Bottom CenterStren 8Stpl Ppr Rubr Push2056564
6/13/24Astra SP Russ (P8)Bottom CenterStren 8Stpl Ppr Rubr Push2077677
6/13/24Astra SP Russ (P12)Bottom CenterStren 8Stpl Ppr Rubr Push2088585
6/14/24Flydear SP (0)Bottom CenterStren 8New20107170.5
6/14/24Flydear SP (P3)Bottom CenterStren 8Stpl Ppr Rubr Push20106565.5
6/14/24Flydear SP (P6)Bottom CenterStren 8Stpl Ppr Rubr Push20147269
6/14/24Flydear SP (P9)Bottom CenterStren 8Stpl Ppr Rubr Push20157671.5
6/14/24Flydear SP (P12)Bottom CenterStren 8Stpl Ppr Rubr Push20178277
6/14/24Flydear SP (10)Bottom CenterStren 8Shaving Face2095754.5

The Flydear blade for the zero and paper measurements, and the one for my face are from different batches. The former was the lone free blade included with a razor I ordered, and the latter was from a tuck. Interestingly, the one from the tuck that I had used to shave my face ten times was the sharpest blade I have measured at any stage. Too bad I didn't take measurements of that blade when new and along the way. I will measure another one from that tuck when I have some more time. I am pretty happy with this 20 data points at (0), (P3), (P6), (P9), (P12) measurement set like I did with the dull freebie Flydear. I will stick with that for a while unless there are good objections. All of the India Astras are from the same tuck. All of the Russia Astras are from the same tuck. This includes previous measurements since the beginning of the project.
 
Leaf Shave Single Edge Blade. This is the dullest blade I have measured, and it doesn't feel especially smooth or toothy. I used it five times to shave my face. It is not a blade I would ever purchase or recommend purchasing, but it was bundled with the razor and I didn't have to cut it in half. It dulled more slowly than sharper blades, but I suspect that is just a function of it starting out so dull.

A blade that can cut the line with 40g force is going to dull much more during 5-10 shaves than one that cuts it at 100g. An exponential trend based on the dimensions of the blade apex makes sense intuitively. The various paper cut tests support this hypothesis, to some extent. It isn't a steep exponential curve, but it is an exponential curve. I suspect you get begone hair shaving capability, 150g force or something, before the curve flattens.

Date6/17/246/17/246/17/246/17/246/17/246/17/24
BladeLeaf (5SE)Leaf (0)Leaf (P3)Leaf (P6)Leaf (P9)Leaf (P12)
LocationCenterCenterCenterCenterCenterCenter
MediumStren 8Stren 8Stren 8Stren 8Stren 8Stren 8
Dulling SubstrateShaving FaceNewStpl Ppr Rubr PushStpl Ppr Rubr PushStpl Ppr Rubr PushStpl Ppr Rubr Push
Measurements202020202020
Std. Dev.464645
Mean857980818687
Median8479.57882.58687
1816775788584
2787482827586
3867376718989
4917878758284
5817473788786
6857580828591
7827678748588
8877987868588
9788376838491
10838786848093
11918082908790
12848079918983
13848077858489
14898185909179
15908785728184
16868176839186
179290878287100
18838678879081
19837477718981
20837775838789

I suspect the jump in cutting force from P3/6 to P9/12 is a statistical phenomenon. I may try 25 or 30 measurement points on the next one.
 
I measured the Assured For Men (AFM) blade from Dollar Tree today. I put some comments about the blade in the current Dollar Tree AFM razor thread.

1000006945.jpg


Date6/18/246/18/246/18/246/18/246/18/246/18/24
BladeAssured FM DTAssured FM DTAssured FM DTAssured FM DTAssured FM DTAssured FM DT
Shaves01P3P6P9P12
LocationCenterCenterCenterCenterCenterCenter
MediumStren 8Stren 8Stren 8Stren 8Stren 8Stren 8
Dulling SubstrateNewShaving FaceStpl Ppr Rubr PushStpl Ppr Rubr PushStpl Ppr Rubr PushStpl Ppr Rubr Push
Measurements303030303030
Std. Dev.4610134892
Median F (g)5766769798126.5
Mean F (g)58647897117159
15767678486182
2556669978387
35968701139894
460588110494107
5577167747972
6616561112121298
762666911798122
8656876778282
96460921057782
1052596491185161
115569729183131
125869709219880
135466899279112
145771928092374
155655701218992
1651677888117397
17585678102100249
18556080989499
195572798784180
2061549377210168
2148677697240135
2254618397104195
235864761029988
2459507510312597
2562709710082314
2668648495175107
2753759410310076
2858688794231138
295660748887301
30576374125123157

It is a sharp and smooth looking blade that loses its edge very quickly.

1000006947.jpg
 
...I changed my testing technique to sample different points along the edge of the blade. I don't know if that makes a difference. Intuitively, it might reduce precision while increasing accuracy, leading to noisier, but more relevant data...

As I understand it, as the DE blade edge wears, it actually "chips out", IOW small sections of the edge break away. That would imply measurements of small segments along the edge could vary quite a lot.

I was wondering if it would make sense to use a testing media that is very wide, instead of the monofilament line. It seems that a wide testing media would do a better job of averaging the measurement over the entire edge and reduce variability.
 
As I understand it, as the DE blade edge wears, it actually "chips out", IOW small sections of the edge break away. That would imply measurements of small segments along the edge could vary quite a lot.

I was wondering if it would make sense to use a testing media that is very wide, instead of the monofilament line. It seems that a wide testing media would do a better job of averaging the measurement over the entire edge and reduce variability.
The Assured blade I used for the paper test definitely has chips and spots where the apex folded over. I looked at it under the microscope, but I binned it without taking any pictures. You can see how there is very localized damage in the numbers where the average cutting force increasingly exceeds the median cutting force as different spots on the blade chip and get damaged. I do make an effort to test various spots along the middle inch of the blade. This is why I don't use a fixed fulcrum. I don't measure (or artificially dull) the outer ends of the edge, because the naturally dulled blades showed a normal curve wear pattern, and I figured it is more useful to know when the business part of the edge has deteriorated compared to the parts that don't do as much work during a shave.

No sane person would regularly use a blade as soft and fragile as the Assured blade, but it does highlight some interesting things because the wear and damage are so exaggerated compared to a blade made of decent metal.

I am looking forward to seeing how this one looks after shaving to dull it more. That should give me a better idea if there is a problem with the test media. A ribbon like medium could have its own problems; if you got to it at an angle, you would have some slicing, reducing force and wear compared to a flat cut. This is why I cut the paper strips on the flat rubber coated plywood surface of a sushi knife cutting board.

The correlation between natural wear and artificial wear seems pretty consistent between the Assured blade and the Astra SPs, so I don't think the artificial wear did anything too crazy to it.

The remaining assured blades might be useful for taking a look at what test media can do to a blade. But if there is significant change, I am not sure it tells us more than that something inevitable is happening. To some extent, unless you are measuring the dimensions of the apex under an electron scanning microscope, then your sharpness measurements are going to cause some wear and chipping at the edge. It is going to be a lot less impact with blades made with proper alloys and heat treatment. As long as I don't keep changing the number of cuts for the tests, then all of the results are still comparable.

The big trend in cutting force is going from one test to the next, not from the beginning of the the test to the end of the test. We don't really see the mean jumping above the median until P9 and P12 tests, so I don't think the major chipping and folding of the edge occurred until the blade was already beyond serviceability. It may have been the test media hitting the dulll blade in one spot at 300g that folded it over, but it doesn't really matter much because it doesn't make sense to shave with a blade that can hold 0.23mm nylon with 300g of force. I had considered skipping P9 and P12 tests because the blade was already completely shot at P6. I just wanted to have the data for comparability in case I ever make a big pretty chart with 50 or 100 blades on it. I also thought it would be fun to show just how horrible this blade is, because I am not sure how many extremely bad blades there are for me to test.
 
The blade above is the new one, not yet used for anything. I wanted to show the coating in that photo. The small chips you see there were like that already. I also took a picture of it after the second shave (and one set of 30 measurements).

1000006965.jpg


Looks smoother, but the apex has certainly widened. The appearance now, with no coating and some face stropping, is similar to a used Astra SP (either of them) that has done ten shaves.

We have another impressive dulling with the second shave.

Date6/18/246/18/246/19/24
BladeAssured FM DTAssured FM DTAssured FM DT
Shaves012
LocationCenterCenterCenter
MediumStren 8Stren 8Stren 8
Dulling SubstrateNewShaving FaceShaving Face
Measurements303030
Std. Dev.465
Median F (g)576673.5
Mean F (g)586473

To put this in perspective, compare this Assured blade, used for two shaves so far, to a Russian Astra SP that was used for ten shaves. The AFM started out much sharper, and ended the second shave duller than the Astra was after ten shaves.

Date6/9/246/9/24
BladeAstra SP Russ (0)Astra SP Russ (10)
LocationBottom CenterBottom Center
MediumStren 8Stren 8
Dulling SubstrateNewShaving Face
Measurements5050
Std. Dev.811
Mean6671
 
I measured the Flydear SP blade again, this time with one from my tuck that I shaved with. I am still getting the highest sharpness measurement from the blade that I used to shave ten times. I suspect it was just closer to the sweet spot in its lifetime of wearing off its coating and then dulling, compared to the other points I collected data with artificial wear. It appears to be a sharp and very consistent blade, with a durable coating and a durable edge.

Date6/19/246/19/246/19/246/19/246/19/246/19/24
BladeFlydear SPFlydear SPFlydear SPFlydear SPFlydear SPFlydear SP
Shaves010P3P6P9P12
LocationBottom CenterTop CenterBottom CenterTop CenterBottom CenterBottom Center
MediumStren 8Stren 8Stren 8Stren 8Stren 8Stren 8
Dulling SubstrateNewShaving FaceStpl Ppr Rubr PushStpl Ppr Rubr PushStpl Ppr Rubr PushStpl Ppr Rubr Push
Measurements303030303030
Std. Dev.7121281520
Median F (g)69.554.556.5687581
Mean F (g)695660697583
F (g) 18356826811765
F (g) 2784149646057
F (g) 37654606897106
F (g) 4686054686595
F (g) 5675756877172
F (g) 67858687467101
F (g) 7715559616869
F (g) 86944886210657
F (g) 9714857589294
F (g) 10726153736880
F (g) 11705445697682
F (g) 12759055775199
F (g) 13724348667891
F (g) 146453557388105
F (g) 155953567478112
F (g) 16695473637188
F (g) 17674668718265
F (g) 186949716955101
F (g) 19565167949453
F (g) 20755782606899
F (g) 21585246645564
F (g) 225956537078122
F (g) 23557955666697
F (g) 24715856607249
F (g) 257359666457112
F (g) 26758758657670
F (g) 27603676585974
F (g) 28615259707462
F (g) 29785556867873
F (g) 30686441738975

It looked normal, fully coated on the honed edge, when new.

1000006971.jpg


It didn't show a ton of damage and chipping after cutting paper and nylon.

1000006974.jpg
 
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