Thread: Analysis of Rotational Cuts. Spoiler: virtually no better than a basic straight cut.

Both of your OPs in starting these threads are well thought out and illustrate your point well IMO. Way more thinking on it than I have given but drawing the same conclusion I've come to from hands on shaving with a straight razor ..... and cutting tomatoes.

Anyway, what I'm beating around the bush in getting at .... is that you ought to put your OP for both threads in the SRP Wiki in the shaving with a straight razor category, Some members get off on the scientific approach. If you don't put it in the Wiki the threads will get lost, buried, in the archives.

Dosen't the size of the object being cut also make a difference? A tomato is much larger than a whisker.

I would also think that the direction of the blade stroke compared to the direction of the hair growth would make more of an impact than any slicing or rotating during the cut.

That's probably what you have been saying heh.

Originally Posted by Shoki

Dosen't the size of the object being cut also make a difference? A tomato is much larger than a whisker.

I would also think that the direction of the blade stroke compared to the direction of the hair growth would make more of an impact than any slicing or rotating during the cut.

At the risk of sounding like I am pretending to have any mathematical aptitude, I'll just say that regardless of the size, the vectors of the cutting strokes are the same, so in my opinion the analogy still stands just fine.

Oh were I only to have enough planes on my face to try all these fancy strokes. I fear that if I tried a scything guillotine rotational rectilinear on my chin, for instance, I'd lose a fair amount of skin and greater amounts of blood in the process. My old whatchamacallit strokes will simply have to do in the (my) face of cowardice or practicality, whatever we're calling it these days.

Originally Posted by JimmyHAD

....is that you ought to put your OP for both threads in the SRP Wiki in the shaving with a straight razor category

Thanks for the idea. I think I need to leave them up here a little while longer for public consumption first. This allows a chance for the community to weigh in - maybe I overlooked a critical variable, maybe the results are ridiculously out of line with experience, etc. The last thread had some pretty reasonable challenges, and the results are more sound for it. If everything holds up under peer review, I will do as you suggested.

@Shoki - the formula I provided in this post takes this into account. The larger the angle from the beginning of the cut until the end of the cut, the more slicing will be involved. In the case of a razor, this angle is nearly zero and thus so is the slicing effect.

I believe chefs would take advantage of this formula with certain rotational cutting strokes. For example, a cut with the point of the toe on a cutting board with the food wedged right up to it, followed by a downward motion from the heel could actually generate a significant slicing motion. Think of it this way: as the blade comes down, there would be a tendency for the food to rotate under the knife. Preventing this rotation would induce slicing. I don't really cook, so this is theoretical - but I would bet this a standard cutting technique taught in culinary schools.

@Bruce - "a scything guillotine rotational rectilinear" is priceless. Thanks for the laugh.

Originally Posted by ixtapalapaquetl

..I had enough definitions that were critical for the analysis already, and didn't think to include others that were less critical. I think you can safely replace any use of the word cut in the OP with the word stroke (and vice versa) if that eases your confusion.

No confusion on my part. Im saying that you are confusing the stroke with the cut. If I am right in this claim then that falsifies your entire "analysis".

Originally Posted by ixtapalapaquetl

The purpose of the analysis was to take a close look at a commonly used stroke...

Obviously you have not thought this through or are not sufficiently familiar with scientific method. Rudimentary trigonometri does not science make.

If "basic straight cut" and "how good" it is isn't properly defined, there is no possibility to claim "better" or "no better than".

You seem to be attempting a quantitative description of the (inherently?) qualitative experience of a bbs-creating stroke of a straight razor?

Originally Posted by hakan

No confusion on my part. Im saying that you are confusing the stroke with the cut. If I am right in this claim then that falsifies your entire "analysis".

Would you mind defining what you mean by stroke and cut? I think this would ease our communication.

Obviously you have not thought this through or are not sufficiently familiar with scientific method. Rudimentary trigonometri does not science make.

I have actually spent a considerable amount of time thinking about this problem. I am reasonably well versed on the scientific method – enough so to know that the scientific method is not appropriate for this application as it is not an experiment-based inquiry. This is instead a mathematical analysis. In mathematics, meaningful concepts are defined, theorems are formed, and these theorems are either proved or disproved using the meaningful definitions. I agree that trigonometry does not constitute science. It is an essential component of science, and the entire field of Physics would be impossible without it, but it is not in itself science. Ad hominem attacks are not science either.

If "basic straight cut" and "how good" it is isn't properly defined, there is no possibility to claim "better" or "no better than". You seem to be attempting a quantitative description of the (inherently?) qualitative experience of a bbs-creating stroke of a straight razor?

The term straight cut has been defined twice - once in the beginning of the prior thread, and once again in the beginning of this thread. The word basic is being used as an adjective indicating that the straight cut is not advanced. I feel the term “basic straight cut” should be reasonably clear to anyone who read either post. If you read the post and still do not know what I mean by straight cut, alas, I have done a poor job indeed.

In both this thread and the prior one, I have repeatedly referred to a slicing motion. This slicing motion lies at the heart of both of these threads. Slicing was defined in two distinct ways at the beginning of the first post of this thread, and in one way at the beginning of the prior thread. In both threads, the quality of a stroke (or cut – I am as of yet unsure of your usage) has been judged accordingly by that measure. Most would agree that a slicing motion is desirable quality, and is a worthy barometer of a shaving stroke (or cut).

I have derived two formulas which do in fact provide a quantitative description of slicing. While the proofs of those derivations have not been provided, they are available upon request. Slicing itself is a relatively simple mechanical action; so simple, in fact, that it would be quite shocking if slicing could not be easily quantified. I agree that there are an untold number of variables related to achieving a BBS shave. But that is not what I am attempting to describe. I am talking about slicing. Just slicing. And it turns out that some strokes (or cuts or whatever) are better at slicing than others.

PS – at some point in replying to you I realized that it should be stated that x must be measured in radians in my second formula. Thanks for the reminder.

You see? I told you that you should have stuck with a knife and a tomato!

Originally Posted by ixtapalapaquetl

Would you mind defining what you mean by stroke and cut? I think this would ease our communication.

Backhand stroke and hitting the ball in tennis? Forehand stroke and hitting the ball? The hitting is one "thing", the stroke another. Same stroke creates different hits depending on an almost infinite amount of variables.
I was going to quote the Oxford dictionary but the entry on cut was, to put it mildly, enormous.

Originally Posted by ixtapalapaquetl

I have actually spent a considerable amount of time thinking about this problem...

Im very sorry for my disrespectful and clumsy formulation in my previous post. Im not even sure my criticism is valid since this isnt a scientific paper. I wasnt entirely paying attention to what I was doing, e.g. posting on the interwebz actually communicating with another human not just the voices in my head.

Originally Posted by ixtapalapaquetl

Slicing itself is a relatively simple mechanical action; so simple, in fact, that it would be quite shocking if slicing could not be easily quantified.

On this we may well have to agree to disagree, and maybe that is the heart of the matter.
I find it hard to see the point of a two dimensional analysis of something like this and critiquing your analysis by something it is not trying to be, is not very helpful of me.

One could say it is downright stupid, but you handled adversity with such aplomb in your earlier thread I thought I could get away with it.

Please have a beer on me:

I gotta go back to lurking. I need to learn how to hone. Once I have learned that I might do some experiments with a knife and a tomato...

kind regards
/H