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

Originally Posted by hakan

One weakness with your analysis is that you are lumping cut and stroke together into one. Is it possible to apply force in different "ways" for the same stroke? That would imply that one stroke can create several different cuts?
This, in turn, forces an analysis of what a "cut" really "is" before a macrolevel study of strokes can be done?

I'm sorry, but I'm not sure I fully understand your point. I will admit that I was loose with the terms stroke and cut, using them somewhat interchangeably. 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. The results of the analysis should hold up in either case as the math won't change. Simply stated, there were no variables assigned to "cut" or "stroke," they were used colloquially.

What is the purpose of this analysis? What do you mean by "no better than a basic straight cut" ?

The purpose of the analysis was to take a close look at a commonly used stroke (there I go again - cut works too) and understand it better. I found that a rotational cut/stroke/motion does almost no slicing through the hair. This makes rotational cuts/strokes/motions similar to straight cuts/strokes/motions - neither slice. It also sets rotational cuts/strokes/motions apart from guillotine and diagonal cuts/strokes/motions, which do slice.

@Shoki - thanks. My MS Paint skills have increased fivefold since starting these little projects. Considering that my final images are still pretty crappy, imagine where I started!

@Malacoda - thanks for the confirmation. It means even more coming from a ME. Never could get into the applied stuff back in college, I was a theory junky. I bailed on NukeE/ChemE for math because of this. I guess I finally found the right application! New major: SRE?

Originally Posted by ixtapalapaquetl

Never could get into the applied stuff back in college, I was a theory junky.

Just take a knife in one hand, place a tomato on a cutting board, ...

Originally Posted by Utopian

Just take a knife in one hand, place a tomato on a cutting board, ...

Wow, I guess that would work too!

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.

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?