I apologise, it's clear I've not struck the right chord. I'd hoped that highlighting the distance between opinion and evidence might defuse the conflict. Perhaps I've inflames it instead.
Illustration of Safety Razor Parameters (Blade Exposure, Guard Span, Blade Gap, Etc.)
- Thread starter ShavingByTheNumbers
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Well, I agree with your main point. You aren't going to be able to completely reduce the concepts "mild" and "aggressive" to a single reliable objective statistic. There will always be a variety of subjective reactions.
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- #63
Yes, "aggressiveness" is subjective. It isn't a dimension like length that can be observed and measured. We get a feel for it and our feelings differ and can even depend on skin and other factors outside of the razor, as you said. Although ratings on aggressiveness vary from person to person, AVERAGE aggressiveness can be modeled as a function of the objective parameters of blade exposure, guard span, blade angle, etc. I've done this with an aggressiveness model that I developed last year but didn't publish because of a lack of validation data. However, for the data that was available, the model matched it very well, surprisingly well, actually. Taking my question in the picture above, it is true that someone might consider the razor on the right with the smaller blade gap as being less aggressive, even though it has considerably more blade exposure, but I'm sure that averaging aggressiveness ratings from users would reveal that the average aggressiveness is larger for the razor with the smaller blade gap in this case. Just look at that beast!
There's no need to apologize, @TheKman. You're right about the distance between opinion and evidence. With more and more objective measurements, each one of us is more likely to figure out what works best for us, and I'd expect different answers. 
Hard data and statistics do only take us so far. You're right about that, @mozartman. My aggressiveness model is just that, a model for aggressiveness, not a definition of it. Rigidity, on the other hand, that increases with decreasing blade deflection, can be defined based on mechanics of materials. Opinions on rigidity are valuable at the moment because there is a severe lack of data (free-end and clamp distances) that would truly help to quantify rigidity. Similarly, there is not much data available for quantifying aggressiveness, but more data would help. Nevertheless, you're right about how "the outcome on one's face would still not be entirely certain" and there "will always be a variety of subjective reactions". We can take objective measurements and output a subjective aggressiveness value, but that doesn't mean that a particular user would agree. Individual aggressiveness ratings would differ around that modeled average value, and the model probably wouldn't be perfect anyway, but it could be a very good guide for comparing and choosing razors, although I favor a more direct and personalized approach of looking at measured safety razor parameters around the blade cutting edge and figuring out what combination of values works best for each individual.
As it showed in the beginning of this thread, the gap has nothing to do with aggressiveness. It will allow for more angles to be used with the razor since the base-plate is further away.
Blade exposure will always determine a razors aggressiveness.
Blade exposure will always determine a razors aggressiveness.
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- #65
Don't forget guard span and blade angle!
Other parameters matter, too, but the main ones are blade exposure, guard span, and blade angle. It's unfortunate how much attention and credit blade gap has received.@ShavingByTheNumbers I think we're on the same page here. A model is exactly what I'm getting at when I say correlation. We can model the relationship, possibly quite well as you suggest, but that doesn't necessarily relate causation for any given measure or group of measures, not without measuring individual effects of each parameter. The fact that you've not published your model indicates to me that you may hold the same reservations I do?
I suppose the thing that frustrate me a little about this conversation is people trying to make a point. Making a point is really about opinion, while objective measurements stand on there own and require no defense. That we're debating anything at all is in itself an indication of opinionated defense of a position. The truth is it's own defense.
Honestly, I find it mentally exhausting trying to word responses such that I don't wind anyone up. But here goes.
On the topic of 'blade gap' as an useful objective measure of performance, this has really been used as a crutch to at least identify something that can be used as a point of comparison between razors or settings or a single razor. If a manufacturer advertised a list of sixteen parameters it would be difficult or impossible for the consumer to make a decision based on the data. So, we list one measurement, flawed though it may be, to assist in the decision making process. There's probably some correlation between perceived aggressiveness and blade gap, perhaps a lot, I don't know, but I think we can agree it's not the whole answer. As a direct measure of performance I think guard span has more meaning that blade gap because it's oriented with the shave plane.
I suppose the thing that frustrate me a little about this conversation is people trying to make a point. Making a point is really about opinion, while objective measurements stand on there own and require no defense. That we're debating anything at all is in itself an indication of opinionated defense of a position. The truth is it's own defense.
Honestly, I find it mentally exhausting trying to word responses such that I don't wind anyone up. But here goes.
To me this is another example of trying to relate a single objective measure to a subjective outcome, precisely the opposite opinion to @weekly in fact. Both positions are right, neither position is wrong. In my opinion blade gap has a relationship to guard span, which makes a difference to my shave. Making a statement of fact based on your opinion/experience may not be true for everyone.
On the topic of 'blade gap' as an useful objective measure of performance, this has really been used as a crutch to at least identify something that can be used as a point of comparison between razors or settings or a single razor. If a manufacturer advertised a list of sixteen parameters it would be difficult or impossible for the consumer to make a decision based on the data. So, we list one measurement, flawed though it may be, to assist in the decision making process. There's probably some correlation between perceived aggressiveness and blade gap, perhaps a lot, I don't know, but I think we can agree it's not the whole answer. As a direct measure of performance I think guard span has more meaning that blade gap because it's oriented with the shave plane.
A large blade gap can be perceived as aggressiveness. I use to use a Parker 94 which had quite a large blade gap and it did feel somewhat aggressive. As was said earlier in this thread each person will perceive how it shaves in his own way.
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- #68
Larger blade gap does usually mean more aggressiveness, but it isn't a hard-and-fast rule by any means. Even if blade exposure and blade angle are the same between two razors, the razor with more blade gap might have less guard span than the razor with less blade gap due to head profile differences, so the razor with more blade gap would probably be considered less aggressive in this case. It's hard to say. We aren't all going to have the same opinion about razors, but on average, parameters like blade exposure, guard span, and blade angle explain a lot about razor aggressiveness that the typical user would feel.
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- #69
I get what you're saying about not confusing correlation with causation. My aggressiveness model doesn't just come from some statistical analysis. The model is physically realistic, based on physical reality and reasoning with respect to cause and effect and fit to the small amount of available data. The reason that I haven't published it yet is because I didn't consider it validated. It fit too well, actually, to the limited data, which made me suspicious. When it seems too good to be true, I especially want more data to challenge it and prove that the model holds up to scrutiny, especially when I was hit with quite a bit of resistance to the idea when I talked about it here. Also, another reason that I held off on publishing the model was that I came up with another model refinement that I needed more data to validate.
An aggressiveness model will not tell someone how he would rate the razor, but it should tell the community how the average user would rate the razor. That means that given different blades, different shaving techniques, different pass orders, different soaps and creams, etc., the model should do a good job of taking razor parameters and outputting the average aggressiveness considered for the razor.
I think that we're on the same page, too. We're having a lively discussion, not an argument, right? There are definitely differences of opinion here, and in the end, I hope that the truth wins out, whether I'm right or wrong about it.
Blade gap is an easy parameter to measure, and since it is only one parameter, it makes razor comparison easier but largely inaccurate since blade exposure is so important. You're right that guard span has more meaning than blade gap with respect to actual performance. I think that each of us could get used to looking at three parameters (blade exposure, guard span, and blade angle) rather than one (blade gap) to find out what works best for each of us, and since we ignore information that we don't care about or don't want to deal with, plenty of us could just ignore the extra parameters.
Speaking solely for me, coming from hard science education and numeracy based professional experience, this work is highly appreciated. If it is duplicative of previous efforts, apologies for ignorance of their existance.
While there certainly exist intangible elements of performance, have found in every realm encountered to date: if it can’t be quantified, it is either due to lack of understanding the proper definition/methodology or it is extraneous but can not presume to speak for others.
However, fail to understand why anybody would object to factual reporting of metrics irrespective of belief in their influence on performance. Not being flippant nor churlish but utterly confounded at the hostility.
While there certainly exist intangible elements of performance, have found in every realm encountered to date: if it can’t be quantified, it is either due to lack of understanding the proper definition/methodology or it is extraneous but can not presume to speak for others.
However, fail to understand why anybody would object to factual reporting of metrics irrespective of belief in their influence on performance. Not being flippant nor churlish but utterly confounded at the hostility.
Right... think I missed that bit earlier. What sort of sample set do you need to validate? I can only make a small contribution here, bit amongst the B&B membership I'm sure it would be simple enough.
And that's the difference between scientists and the rest of the population really. I couldn't care less if my opinion is correct or not. Provided the evidence is valid I'm more that happy to be wrong.I think that we're on the same page, too. We're having a lively discussion, not an argument, right? There are definitely differences of opinion here, and in the end, I hope that the truth wins out, whether I'm right or wrong about it.
Reading between the lines a little here, can I assume the model is based largely on these three dimensions? Perhaps we should be recommending a shift towards these three and away from blade gap?
I really want to get the camera out and work up some data on what I have now, just to satisfy my own feeling on what parameters are meaningful to me.
See point above about the difference between scientists and normal people.
Chan Eil Whiskers
Fumbling about.
If I've missed previous answers to my questions I apologize.
Could you define guard span and cap span? They are measured from the blade cutting edge to exactly where?
Is clamp distance the distance from the blade cutting edge to where the blade is clamped in a vise like fashion by both the cap and the baseplate?
One end of the free-end distance is the blade cutting edge. What is the other end exactly? What is the importance of the free-end distance?
I may have a few more questions, but without knowing the answers to the questions I just asked I don't know.
Your illustrations and the work and thought which went into all of this great stuff is greatly appreciated.
Thanks.
Happy shaves,
Jim
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- #73
Above is the updated version of my illustration, as posted in this thread on October 23rd (B&B URL). Imagine a flat surface pushed against the razor head, through the blade if necessary, so that the flat surface touches both the guard and cap. That's the neutral shave plane. The guard span is the distance along the shave plane from the blade cutting edge to where the guard and shave plane meet. The cap span is the distance along the shave plane from the blade cutting edge to where the cap and shave plane meet. The neutral shave plane has both a guard span and a cap span. The steep shave plane has only a guard span. The shallow shave plane has only a cap span.
Yes.
The other end is the point where the blade contacts the cap. The blade is a "free end", as engineering people would say, over that region. The blade is cantilevered from the clamp to the free-end contact point to the blade cutting edge. For some razors, the blade is free right off of the clamp, so the blade is simply cantilevered in those cases. The importance of the clamp and free-end distances is that they relate to blade rigidity. (That is noted in the updated picture above.) In general, longer clamp and free-end distances cause more blade deflection and less blade rigidity.
I'm glad to help, Jim. Thanks for the kind words. If you have more questions, please let me know.
Chan Eil Whiskers
Fumbling about.
Thank you so much.
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- #75
I'm glad that you appreciate it.
As far as I know, my illustration is the most comprehensive out there for parameters around the cutting edge. Based on an Internet search, it looks like I'm the first to talk about a "neutral" shave plane and blade angle, for example. @Cal helped me refine the illustration, so he can attest to its origination.I agree that with more understanding, with more measurements, we can better quantify performance, I think greatly so. There are people like us that appreciate this stuff and there are others that are resistant to it because of what they believe to be true about blade gap or because they just don't care about measurements or feel that measurements take away from the art and fun of shaving. That's my two cents, anyway.
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- #76
Right... think I missed that bit earlier. What sort of sample set do you need to validate? I can only make a small contribution here, bit amongst the B&B membership I'm sure it would be simple enough.
And that's the difference between scientists and the rest of the population really. I couldn't care less if my opinion is correct or not. Provided the evidence is valid I'm more that happy to be wrong.
Reading between the lines a little here, can I assume the model is based largely on these three dimensions? Perhaps we should be recommending a shift towards these three and away from blade gap?
I really want to get the camera out and work up some data on what I have now, just to satisfy my own feeling on what parameters are meaningful to me.
See point above about the difference between scientists and normal people.
Yes, my aggressiveness model is based on blade exposure, guard span, and blade angle. Those are the three most important parameters, and yes, I recommend a shift towards these three parameters and away from blade gap. Unfortunately, blade gap is the only parameter that is easy to measure. The other ones take more work and finesse. Every time I analyze a razor with photo analysis, I get better at it and improve my methodology. I recently finished taking photos and making physical measurements for the Bevel razor. As usual, my methodology has improved, but this time, it has really improved as I've incorporated so many more physical measurements and better photos for digital measurements. I've also made setup easier by making a great adjustable razor stand for vertically propping up a razor for most of the photos, and I also made a stand to vertically hold my little metric scale. You'll probably see pictures of these items in my Bevel post whenever I get to it. I hope that you do try to do some photo analysis and make physical measurements. There is a lot to the analysis that I do, which I plan on explaning in more detail with the Bevel post in the future, but one can eyeball and estimate a lot of parameters and use simple tools like a protractor and a metric scale or ruler. My analysis takes much more time to yield accurate and precise measurements.
Great work, @ShavingByTheNumbers, and this last observation is on point, I think. Of course, because among other things, our faces and necks are not identical and not made up of flat, rigid surfaces, I don't expect these three parameters, or any other set of parameters, to tell the whole story. But they would be useful, and likely more useful than blade gap alone, I think. With more data from you, maybe we'll get to put your theory to the test.
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- #78
Great work, @ShavingByTheNumbers, and this last observation is on point, I think. Of course, because among other things, our faces and necks are not identical and not made up of flat, rigid surfaces, I don't expect these three parameters, or any other set of parameters, to tell the whole story. But they would be useful, and likely more useful than blade gap alone, I think. With more data from you, maybe we'll get to put your theory to the test.
What you said, @mozartman, is very true. Blade exposure, guard span, and blade angle don't tell the whole story, but the story they tell is orders of magnitude better than blade gap. I'm going to keep making measurements, and hopefully if others get involved, we can produce enough data and/or get manufacturers to provide measurements to change how people choose safety razors. That would be something!
As usual, @ShavingByTheNumbers , your work is encyclopedic. Thanks for putting in all the effort, I'm impressed every time.
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- #80
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