Thread: Standard Reference Material for Hanging Hair Test

Originally Posted by Sticky

Sharpness tester

Of course, the test media isn't exactly equal to a hair... Not sure about consistency. Reasonably objective, and made for the purpose. Also more than I'd want to spend, considering our practical application goals (for sharpening/tooling/hone comparison).

Classic...

The last line on that tester

"Note As this system is different to the ISO 8442.5 testing technique for sharpness measurement the results from this system are not directly comparable as the cutting performance of any specific blade or knife varies dependant on the material being cut. For example a razor blade is great for shaving , but is useless at cutting down trees! "

These recent comments are of the "half empty" vs. "half full" variety.

There are those who believe "all or nothing", and those who believe in "something".

King Camp Gillette became one of the wealthiest men of his time by believing in "something" (called in industry "interchangeability of parts"). See:

http://findarticles.com/p/articles/m...4/ai_77826059/

"The stubble-chinned utopian had just dreamed up the world's first disposable razor blade. It took him five years to find someone who could provide a machine that would automatically hone thin sheets of steel to the required sharpness, and at first the blades sold for less than they cost to make. Undaunted, Gillette forged ahead and eventually had a second epiphany: He would give away a razor and sell the blades. By 1910 Gillette dominated the razor business, and its founder was a millionaire."

Since then billions of single-edge and double-edge blades and disposable razors have been made and sold. Were these factory-made blades "shave-ready" or not? The believer in "all or nothing" says "not", because each blade needed be be tuned to the individual face, so some individuals got poor shaves with them. The believer in "something" would say "even if 'not', it's a good start", and make $ millions from those for whom they are acceptably "shave-ready".

In all the threads on honing I have read at SRP, not one that I remember said: "Don't test or look at the edge at all during the entire process. The only test you should ever do is shaving at the end. Any other method will result in an unacceptable blade." (This is the "all or nothing" argument.) Lynn Abrams says "I rely on the thumb pad test for setting bevels." (He's obviously a "something" kind of guy. If it works, he uses it, even though he still does a final shave test each time.)

I was talking to Lynn a couple of weeks ago and mentioned that it occurred to me that my skill at shaving has improved to the point where I might get a great shave from a razor that was not as sharp as it could be even though it would pass the HHT. So now even the celebrated HHT leaves some doubt in my mind that I had achieved the ultimate sharpness I've been chasing. I used to post early on that I didn't think my extremely fine, fly away, hair could work for HHT.

Then one day I got the bright idea to try it with a Feather DE blade. I am officially a senior citizen and my hair is a mix of gray, white and transitioning from brown to gray. Some of it is so thin and pale that I have a hard time seeing it when I am holding it to do the HHT. I have to move my hand back and forth, or side to side, and work in good light with a back ground that allows me to see the hair. Even a new Feather DE blade won't always cut my HHT.

The hairs on my head are not all the same. Some of them are extremely fine while some of the darker hairs are thicker and may cut more easily. I have gotten fine shaves from razors that wouldn't pass the HHT but got to a point of obsession with HHT. I found that if I have a razor that won't pass I can keep working on it until it will, so I do. I've also found that one that will pass won't necessarily give me a better shave than one that won't pass.

I've read that for best results the hair should be held root out and I do that. It should be freshly washed and I don't do that. I pull one out of my greasy hair brush and have at it. More often than not , nowadays, it cuts. The mono-filament idea is intriguing and it would be great to have a quantifiable substance to do that test. For now I will stick with my own hair since it is difficult enough.

Originally Posted by Alethephant

In all the threads on honing I have read at SRP, not one that I remember said: "Don't test or look at the edge at all during the entire process. The only test you should ever do is shaving at the end. Any other method will result in an unacceptable blade." (This is the "all or nothing" argument.) Lynn Adams says "I rely on the thumb pad test for setting bevels." (He's obviously a "something" kind of guy. If it works, he uses it, even though he still does a final shave test each time.)

I went back through this thread, and did not see anyone use the "all or nothing" argument that you refer to.

All people are saying is that even if you design a test to compare how well different razors cut a piece of filament, what you end up with is a test of how well razors cut a piece of filament. It doesn't necessarily translate to a test of shave readiness... For someone that doesn't have other calibrated tests to determine how they are doing with their honing, might it be useful? Maybe... But, it still doesn't translate to a test of shave readiness. Maybe that's not what you intend for it to be...

Oh, and I'm assuming you meant Lynn Abrams above.

Thanks for pointing out the typo, which I've fixed in the posting.

Actually, you yourself are making a type of "all or nothing" argument here: "what you end up with is a test of how well razors cut a piece of filament. It doesn't necessarily translate to a test of shave readiness... But, it still doesn't translate to a test of shave readiness..."

This is equivalent to saying something like: "If you don't measure ALL of the variables involved, you won't get ANYTHING (i.e., NOTHING) useful from the test." This is fallacious. The answer is not a dichotomy: all or nothing. It is a trichotomy: all, something or nothing. So this sets up a "straw man" that is easily demolished by simple rhetoric. No, it doesn't necessarily translate into a test of shave readiness. But, equally, it doesn't necessarily NOT translate into a test of shave readiness either.

So the real question isn't "If razor PASSES the FCT, that doesn't necessarily mean it's shave-ready.". The important question is the reverse: "If the razor FAILS the FCT, what does this mean about about shave-readiness?" If it means SOMETHING, then it is useful. The opposite of ALL is not NOTHING.

Others have voiced or referred to similar arguments:

"That an even unreliable HHT to determine 'Sharpness' has never been a question, that it has nothing to do with 'Shave Readiness' has always been the debate." Again, the idea that the opposite of "all" is "nothing".

"... so even if you can prove you've gotten the sharpest edge out of a razor with numbers, I am still not willing to accept this as a well honed edge until I have shaved with it." The implication is that verifying sharpness is worth nothing. But what if you verify dullness?

I am not suggesting that shaving is not a good test for a particular person of "shave-readiness", even though the measurement is subjective, skill sensitive, idiosyncratic and time unstable. Certainly it is the endpoint outcome of primary importance, so it is the objective of all of this. I am not also suggesting that "shave-readiness" is not a happy conjunction of multiple important variables, some of which are person idiosyncratic and some of which are razor idiosyncratic. Sharpness alone is probably not completely sufficient (others might be bevel angle, shaving angle, type of steel, type of hair, growing angle, microstructure of edge, etc.), but I am sure it's probably at least 80% of the issue. Otherwise a commercial disposable razor or blade would be a flop.

If you make a measurement, it is useful if it correlates with the desired outcome. It doesn't have to correlate perfectly. It only has to correlate enough to be useful.

If the FCT didn't correlate at all with my subjective opinion, I wouldn't continue with it. But so far it has near 100% correlation for me. It also correlates fairly well with my HHT. These are both promising.

However, I am open to the possibility that, once basic good sharpness occurs, then sharpness may no longer correlate with improvements in shaving. Those might relate to other factors. This would also explain the division into camps on SRP. For beginners, attaining initially useful level of sharpness is difficult, so sharpness is the central issue. Thus the HHT interest. For experts, all razors used are very sharp, so very small improvements in sharpness are no longer correlated with significant improvements in shaveability. Something else is going on.

The key question is then: "If two razors differ detectably in sharpness, do they also differ detectably in shaveability, or is this only true for some range of sharpness?"

As an empiricist, I await the outcome of further experimentation. From the results I'll see where the usefulness of the FCT starts and ends.

Originally Posted by Alethephant

However, I am open to the possibility that, once basic good sharpness occurs, then sharpness may no longer correlate with improvements in shaving. Those might relate to other factors. This would also explain the division into camps on SRP. For beginners, attaining initially useful level of sharpness is difficult, so sharpness is the central issue. Thus the HHT interest. For experts, all razors used are very sharp, so very small improvements in sharpness are no longer correlated with significant improvements in shaveability. Something else is going on.

The key question is then: "If two razors differ detectably in sharpness, do they also differ detectably in shaveability, or is this only true for some range of sharpness?"

Good grasp of things, here. I say go for it.

One point to mention, in case it should prove helpful: I found that small changes in the tension of the thread (in my case) resulted in large differences in the amount of force it took to cut it. Instead of hand-winding--if I'm reading that correctly--you really need some way of ensuring that the tension on the line is the same each time. On my crude setup, weighting one end of the line seemed to work fairly well, but there are surely other ways of doing it, too.

EDIT: Just saw your comment at the end of post #15 about "constant deformation rate". I believe that's what I'm getting at.

The tension and deflection rate would show up as increased variation (inconsistency). That doesn't appear to be happening. In fact, right now I don't know if the accuracy of the force gauge isn't the single largest error in the system.

Despite hand winding, hand pressing, off-angle winding, different spools of line and other issues, the standard deviation is still down in the 6-10% range, which is typically about as good as can be expected in these tests.

So, at the moment, I have no real motivation to try to improve the arrangement: It's good enough.

I think the type of filament is important in some of the issues you mention. For example, if the line stretches or doesn't stretch, the amount of tension might be very important.

Revision 2 of the FCT ("Filament Cut Test").

This is a piece of wood 3.5" long, with two 4d nails at 0.5" and 3.0". I also bored two 3/32" holes on the ends for a piece of round toothpick to peg down the line. There is a center 3/16" hole to screw the 10x32 bolt end of my DFI2 force gauge into.

My DFI2 gauge remembers peak force in grams (unfortunately no decimal). It also has a computer interface. It's measurement rate is 400 sps, with the meter reading an average of 40 samples and the peak reading instantaneous. I will connect this up later and get some force-time curves. (If I connect to the motorized test stand, I can get force-deflection curves.)

The filament deflects a cm or so before breaking, so I don't think slack is a big issue.

I carry out the rev. 2 test as follows: Peg the filament down one side. Draw taut up to the first nail and wrap with two loops. Pull taut over to the 2nd nail and do two loops. Pull taut down to the other edge and peg down it down. Zero the meter. Then take the razor and press slowly down perpendicular to the filament at the center of the span. After fracture, record the peak value captured.

With this setup, I obtained the following values:

Black (Fermarud) razor:

After honing, before stropping: 36 g
After stropping: 29, 30 g [previous jig: 28 g]
Hanging hair test ("HHT"): Ok to Good (50-75% success)
Shave test: Poor (snags on chin)
(There is a known honing problem with this razor I haven't fixed yet: It doesn't lie flat at the heel.)

White (Fermarud) razor:

After honing, before stropping: 36 g
After stropping: 21, 23 g [previous jig: 25 g]
Hanging hair test ("HHT"): Very Good (100%)
Shave test: Fair (some snagging over chin)

SuperMax DE blade, new: 14, 16 g [previous jig: 12 g]

The first and second versions of the FCT were done with different jigs and different spools of filament.

Conclusions:

1. Good reproducibility, particularly given hand driven deflection, different spools and different test jigs.

2. Repeatability appears to be a standard deviation of about 1.6 g, or a relative standard deviation of 11% for the lowest value and 6-7% for the highest values. Appears to be a constant error rather than a constant relative error. This should clarify in more extensive testing.

3. Correlates well with my HHT.

4. Correlates well with shaveability.

5. I'm happy with the current jig. It appears to satisfy my needs with a minimum level of effort. It is a little time-consuming reloading filament. I don't have any good ideas on how to speed things up, other than having a better lockdown arrangement.

See pictures attached.

I totally disagree. How an edge LOOKS is totally qualitative, not quantitative.

Quantitative would be like: It takes X neuton meters of force to cut through a 1/16 inch standard monofilimant line. A measurable and somewhat repeatable measurment.

Qualitative is: It looks sharp. It shaves nice.

Originally Posted by gugi

Actually this doesn't quantify sharpness, for that you need a really good microscope. This quantifies the ability to break fiber.

Gillette and Schick use polymers to reduce the friction so that the edge cuts easier. Almost all of us use water and soap to change the properties of the hair so that it breaks easier.
When you start breaking down the process of shaving the sharpness of the razor is one of the less important factors.

And as far as quantification goes, if you venture to other forums and ebay you'd be surprised how advanced some people are at quantifying it.



Interestingly enough a sentence like this tells me everything I want to know about that honester, so I guess for me it works really well.

I think what gugi was trying to say was, if an edge is well-honed and polished, sharpness is primarily a function of the geometry (bevel angle) of the edge. The sharper the angle, the sharper the blade. Of course this doesn't apply if the edge microstructure is not an intersection of perfect planes.

What gugi does say that appears totally at odds with all advice given on SRP to beginners: "When you start breaking down the process of shaving the sharpness of the razor is one of the less important factors." On the contrary, the typical advice is to get a "shave-ready" razor before starting.

This suggests that sharpness of the razor is the single most important factor. In fact, if you think about it, the very nature of a razor that distinguishes it from all other blades is its sharpness. The closest other blade is a chisel, which shaves wood instead of hair. Sharpness is also the most important factor in performance of a chisel.