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DE razor geometry. A system for measuring aggressive razors.

APBinNCA

Contributor
Lol. Don't be sorry, you were actually right. Blade exposure is measured perpendicular to the shave plane, which is not what I was doing.

The corrected blade exposure measurement I get is .157mm, which is bigger than the .13mm stated by the manufacturer, but I'm pretty happy with being within a few hundredths of a mm. The gap is only off by a few hundredths of mm too, which I'm pretty happy with. It looks like a reasonably accurate way to get measurements with $40 worth of equipment. Once you have the picture, it's about 5 minutes worth of work to get measurements.

I think ImageJ will probably do a better job than my proof-of-concept attempt with Powerpoint, especially if "focus stacking" can make the reference lines a bit crisper. Here are the updated measurements:

As mentioned by SCh5 about the gap not being perfectly parallel the the plane of the handle, the camera has a slight tilt. I know you are going to try to get some better pictures to work with, so don't take this wrong, you are working with what you have. I grabbed an angle finder and a razor and estimated an approximate tilt of 3 degrees. To visualize what that can do, think about photographing buildings. There is probably too much going on to make guesses about this image, but I would believe the differences you are getting are a compound effect of several distortions. I could probably derail this into a discussion about field curvature of optics, but that's enough for now. I have ideas about how to make a DIY comparator.
TLDR: you did a good job with what you have.:001_cool:
 
Data Science, categorical vs numerical data:
With categorical data, you have an intuitive description of a sample (here sample = safety razor), but cannot compare. E.g. given categories mild and mild-to-aggressive, you cannot compare 2 samples from each category, provided that 1 sample has e.g. P/Exc/whatever and the other Nt/Min/whatever.
With numerical data, you can compare samples. Programming a classifier is trickier though, as noted by @Dovo1695. Also, I agree with you that the numbers can get overwhelming for new wet shavers.
I'm not sure whether @Slock wants to be able to compare razors or just label them "mild" vs "aggressive". I would prefer the former.
I think I would like the former as well. Something better than blade gap which seems to be the measurement the manufactures are using most. Some even use it in their razor names.
 
As mentioned by SCh5 about the gap not being perfectly parallel the the plane of the handle, the camera has a slight tilt. I know you are going to try to get some better pictures to work with, so don't take this wrong, you are working with what you have. I grabbed an angle finder and a razor and estimated an approximate tilt of 3 degrees. To visualize what that can do, think about photographing buildings. There is probably too much going on to make guesses about this image, but I would believe the differences you are getting are a compound effect of several distortions. I could probably derail this into a discussion about field curvature of optics, but that's enough for now. I have ideas about how to make a DIY comparator.
TLDR: you did a good job with what you have.:001_cool:
Thanks. I'm pretty happy with the results. What I like best about it is that pretty much anybody can do it with a reasonable degree of accuracy in 5 minutes and with $40 worth of equipment. I think the error can be reduced by 80% with some pretty simple steps.

Considering that RazoRock is industry leading just by listing the exposure as either "Positive", "Negative" or "Neutral", I'd say a few hundredths of a mm is pretty an acceptable level of error! 😃

I'll be curious to see your thoughts an a DIY comparator. I had a crazy idea about using an old slide projector and a transparent ruler with opaque markings, and then taking measurements from the enlarged projection on a whiteboard, but it seemed like an "off the wall" way to get measurements...
 
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As discussed elsewhere in the thread, ordinal measurements of blade exposure like "positive", "negative", and "neutral" are a valid approach, and it's a lot easier to do. For those that prefer this, @Ron R has an interesting methodology that he has shared elsewhere. It doesn't require microscopes, cameras, computers; or anything else complicated. Here is a link:

 

Esox

I didnt know
Moderator
I registered just to post this, sorry if it's crap:
SIN(x)=Opposite/Hypotenuse so
SIN(19)*.4=.13
Therefore, guessing, exposure is perpendicular to the plane of shaving
Aaron
I was going to link this thread in your Newbie Check-In thread when I read this;

I am technically minded and that isn't always appreciated so I will use the popular YMMV disclaimer when I don't want to find sources or sound overly nerdy.
Obviously, that wasnt needed lol.


especially if "focus stacking" can make the reference lines a bit crisper.
That image has a single focus plane. Higher resolution of the image and the ability to work with RAW image files prior to adding layers would help the clarity as would using .png instead of .jpeg when enlarging.


but I would believe the differences you are getting are a compound effect of several distortions.
Barrel and pincushion distortions can be corrected in Adobe CS5 that I use, and likely other photoshop programs, as well as the Chromatic Aberration that comes with correcting them.
 
To visualize what that can do, think about photographing buildings. There is probably too much going on to make guesses about this image, but I would believe the differences you are getting are a compound effect of several distortions. I could probably derail this into a discussion about field curvature of optics, but that's enough for now.
You are correct, @APBinNCA. The aberrations caused by the lens of my Plugable USB make it difficult to make accurate measurements. That is why I center the edge of the blade with crosshairs. It does a pretty good job for $40.
I am looking into getting a real optical comparator, but they do get pricey, even used.
 
That image has a single focus plane. Higher resolution of the image and the ability to work with RAW image files prior to adding layers would help the clarity as would using .png instead of .jpeg when enlarging.
As far as error reduction goes, here are the things I was thinking might help with measurement accuracy:

1. Include a steel ruler on the same plane as the side of the razor in the photo for scaling.
2. 2 photos at two different focal lengths. One focused on the side of the razor at the shave plane, one on the blade itself. Focus stacking in ImageJ to combine the two photos for crisp focus at all points. Crisp reference lines make a big difference.
3. For extra accuracy, it would help to flip to the razor 180 degrees and do it again. Average the results from the two sides of the razor. This will account for blade skew on all razors, but especially on razors like the Fatip Grande.

I guess the question becomes "how accurate is "good enough"? There is always a trade-off between accuracy and complexity/cost. It's a purely a personal preference thing, but my goal is a methodology takes less than 5 minutes, and is accurate to +/- 5% and costs less than $50 in equipment. That seems pretty feasible to me.

That said, if accuracy of +/- 2% is possible within the same 50/5/5 constraints, I'd be even happier! Distortion correction in Adobe CS5 certainly seems intriguing.
 
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Esox

I didnt know
Moderator
In this crop of your picture on the previous page, the distortion from enlarging is what I think you want to eliminate.

Screenshot 2021-06-10 at 13-34-17 DE razor geometry A system for measuring aggressive razors .png

I see your original image is a .png file so you would need higher resolution than that camera is capable of providing. If that image had the resolution of this one, think how sharp it would be when enlarged and cropped.

props.jpg

Lower cost USB microscopes arent meant for that level of detail but like you say, how much accuracy do you need? Think of a camera like you might a race car. How fast do you want to go? Speed is directly related to money lol.
 
In this crop of your picture on the previous page, the distortion from enlarging is what I think you want to eliminate.

View attachment 1279708

I see your original image is a .png file so you would need higher resolution than that camera is capable of providing. If that image had the resolution of this one, think how sharp it would be when enlarged and cropped.

View attachment 1279713

Lower cost USB microscopes arent meant for that level of detail but like you say, how much accuracy do you need? Think of a camera like you might a race car. How fast do you want to go? Speed is directly related to money lol.
Yeah, and 8000x8000 picture would be pretty awesome. I'm guessing that wouldn't be cheap unfortunately. I've never tried the Pluggable USB 2.0, but the pictures I've seen in the reviews on Amazon make me wonder if it isn't capable of more if focus stacking is used.

What impresses me with @Rosseforp's photos is that it really maximizes focus all over with just one focal plane. If that constraint was lifted, I think it might be able to get even closer.

Doug, have you ever taken the closest shot you can take with the Pluggable of just the razor blade itself? That would be super interesting to see.
 
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Esox

I didnt know
Moderator
Yeah, and 8000x8000 picture would be pretty awesome. I'm guessing that wouldn't be cheap unfortunately. I've never tried the Pluggable USB 2.0, but the pictures I've seen in the reviews on Amazon make me wonder if it isn't capable of more if focus stacking is used.

What impresses me with @Rosseforp's photos is that it really maximizes focus all over with just one focal plane. If that constraint was lifted, I think it might be able to get even closer.

Doug, have you ever taken the closest shot you can take with the pluggable of just the razor blade itself? That would be super interesting to see.
Screenshot 2021-06-10 at 14-03-46 Design215 Megapixels and Print Size Chart.png

Even 20mp cameras are easy to come by today but I'd so some reading of reviews about macro use before deciding. The Canon S5 IS I used for taking the picture of the broken rifle bolt only has a resolution of 6mp. The lens quality and internal image stabilization did the rest.

There have been a few threads showing blade edges microscopically.

The Eye Test. The Old Timer (Polsilver SI) VS The Young Whippersnapper (Wizamet SI) - https://www.badgerandblade.com/forum/threads/the-eye-test-the-old-timer-polsilver-si-vs-the-young-whippersnapper-wizamet-si.606677/#post-11239868

loupe v microscope - https://www.badgerandblade.com/forum/threads/loupe-v-microscope.602799/

A photography loupe, hmmm.

Loupes & Magnifiers | Magnifying Loupes | B&H Photo - https://www.bhphotovideo.com/c/buy/Loupes-Magnifiers/ci/987/N/4077634476
 
View attachment 1279722

Even 20mp cameras are easy to come by today but I'd so some reading of reviews about macro use before deciding. The Canon S5 IS I used for taking the picture of the broken rifle bolt only has a resolution of 6mp. The lens quality and internal image stabilization did the rest.

There have been a few threads showing blade edges microscopically.

The Eye Test. The Old Timer (Polsilver SI) VS The Young Whippersnapper (Wizamet SI) - https://www.badgerandblade.com/forum/threads/the-eye-test-the-old-timer-polsilver-si-vs-the-young-whippersnapper-wizamet-si.606677/#post-11239868

loupe v microscope - https://www.badgerandblade.com/forum/threads/loupe-v-microscope.602799/

A photography loupe, hmmm.

Loupes & Magnifiers | Magnifying Loupes | B&H Photo - https://www.bhphotovideo.com/c/buy/Loupes-Magnifiers/ci/987/N/4077634476
Even with the $40 Pluggable USB 2.0, I think it's possible to increase resolution by 650% by zooming in a bit closer. When I drop it in powerpoint, the image is 13.33" x 7.5" 100 square inches. The red area in the center of the pic still captures everything of interest in terms of measuring razor performance characteristics: Exposure, Gap, Guard Span, Free End Distance etc but it's 2.92"x 5.19"= 15.16 square inches. That should be 6.5x higher resolution of the area of the small red rectangle. I think.

Again, I know even less about optics and microscopes than I do about photography, and which is to say it rounds to zero. If it was possible though, I think it would dramatically increase accuracy of measurements just by doing that alone.

 

APBinNCA

Contributor
I think measuring blade exposure is the biggest hurdle to creating a system for scoring razor aggressiveness. Blade is plays a larger role than every other parameter put together, but it's unknow for 99% of razors. The reason for this is that blade exposure is too small to be seen with the naked eye. The only way to really get that information as far as I can tell is a closeup photograph of a razor with a perfect blade loaded, with a known scale, and then measure the distance in the photo using a program like ImageJ.

There are two fundamental problems with this. The first problem is that photographing a closeup of a razor correctly in order to measure blade exposure is challenging. The second is that exposure is dependent upon the razor blade used, because essentially no blade is actually 22mm.

I wrote a summary of how I thinking of tackling that problem and the equipment that might get the job done in the link below. All it takes is a $40 USB microscope and some open source software:


There may be better ways to go about it, but it's what makes sense to me when I wrote it. As it turned out, there was actually somebody who was already using the Pluggable USB 2.0 to take profile shots of razors. Here are some of his photos. If they had a small steel ruler in them, it would probably be enough to take decent measurements in 5 minutes with something like ImageJ. For that matter, you could probably get the job done accurately enough in PowerPoint just by going to Format>Size & Position and measuring the length of a line segment corresponding to 1mm on the ruler, and then measuring the line segment of blade exposure. That would good enough for government work.

Here is @Rosseforp's setup:



Karve SBD .98mm



Karve OCD .98mm


Timeless .95mm


Here is an example of a crappy photo taken by me, but with a ruler for scale:
I have been following this saga since the beginning, but it is now across three threads. I am going back and re-examining things to see if there is anything useful I can contribute without duplicating others. The one stand out so far is that you are using the image for the Karve SBD, but the image for the OCD is flatter. You can visibly see less blade exposure. Same with the Timeless 95 which has a 0.05 exposure. Maybe go back and do measurements on those images and compare how close you can get them to the one you already did?
 

APBinNCA

Contributor
It appears the USB microscope you are using or contemplating has a semi-translucent base with some kind of grid. My initial idea for a DIY comparator is to put the microscope on a light box or some sort of light source to create a high contrast image(back lighting). I played around with this using my phone just to see if my lighting idea will work and it does. It is much easier to define a profile in a digital image in near black and white because all imaging software applies some kind of both color and sharpness correction. If you are only dealing with luminance, you should be able to grab the edges with your digital measurement easier. Unfortunately, the razor feature sizes are too small for a phone camera so I can't post any useful pictures.
 
The one stand out so far is that you are using the image for the Karve SBD, but the image for the OCD is flatter. You can visibly see less blade exposure. Same with the Timeless 95 which has a 0.05 exposure. Maybe go back and do measurements on those images and compare how close you can get them to the one you already did?
Good catch @APBinNCA :punk:

I was eyeballing the edge of the blade trying to get the best picture of the blade edge, and the razor wasn't completely straight. These pics were taken with the razor properly straightened. :hand: Just like you pointed out.

Looking at the differences in my first pictures and these makes it easy to see how difficult it is to make accurate measurements with inexpensive testing equipment.

Karve SBD
SBD1.jpg
Karve OCD
OCD1.jpg

And to satisfy @Dovo1695, with greater magnification. The difference in heights of the side of the razor and the end of the blade makes it impossible to get both in focus at the same time, so I adjusted the focus in between.

Karve SBD
SBD2.jpg
Karve OCD
OCD2.jpg
 

APBinNCA

Contributor
I am glad you weren't offended at my nitpicking, I forgot who's photos he was using! I discovered just how hard it is to get straight on photos while playing around with my phone camera. I suppose the repeatability may be the first obstacle to overcome as has been mentioned somewhere by @Dovo1695. I guess a jig needs to be designed, but that is out of my wheelhouse!:biggrin:
 
As far as error reduction goes, here are the things I was thinking might help with measurement accuracy:

1. Include a steel ruler on the same plane as the side of the razor in the photo for scaling.
2. 2 photos at two different focal lengths. One focused on the side of the razor at the shave plane, one on the blade itself. Focus stacking in ImageJ to combine the two photos for crisp focus at all points. Crisp reference lines make a big difference.
3. For extra accuracy, it would help to flip to the razor 180 degrees and do it again. Average the results from the two sides of the razor. This will account for blade skew on all razors, but especially on razors like the Fatip Grande.

I guess the question becomes "how accurate is "good enough"? There is always a trade-off between accuracy and complexity/cost. It's a purely a personal preference thing, but my goal is a methodology takes less than 5 minutes, and is accurate to +/- 5% and costs less than $50 in equipment. That seems pretty feasible to me.

That said, if accuracy of +/- 2% is possible within the same 50/5/5 constraints, I'd be even happier! Distortion correction in Adobe CS5 certainly seems intriguing.
Yes if you need a $12,000 worth of photo equipment to do this you might as well buy all the razors you want until you find the perfect one for you.
 
I took these pictures at the same height and focus as the razor pictures to see if they can help with calibration.
WIN_20210610_15_45_05_Pro.jpg
Each mark is .01"
WIN_20210610_15_48_56_Pro.jpg
I placed a .100" Johansson gage block on the scale to show the effects of moving off center.
WIN_20210610_15_41_26_Pro.jpg
On center the edges of the Jo Block are clear and sharp.
WIN_20210610_15_42_14_Pro.jpg
The side of the Jo Block can be seen as it is moved to one side as a ghost mirror.
WIN_20210610_15_42_43_Pro.jpg
With a true Optical Comparator the sides would not show.

It is much easier to define a profile in a digital image in near black and white because all imaging software applies some kind of both color and sharpness correction. If you are only dealing with luminance, you should be able to grab the edges with your digital measurement easier.
:cornut:
 
I am glad you weren't offended at my nitpicking, I forgot who's photos he was using! I discovered just how hard it is to get straight on photos while playing around with my phone camera. I suppose the repeatability may be the first obstacle to overcome as has been mentioned somewhere by @Dovo1695. I guess a jig needs to be designed, but that is out of my wheelhouse!:biggrin:
Not at all. As you can see, it forced me to take better pictures!!!!!
 
Good catch @APBinNCA :punk:

I was eyeballing the edge of the blade trying to get the best picture of the blade edge, and the razor wasn't completely straight. These pics were taken with the razor properly straightened. :hand: Just like you pointed out.

Looking at the differences in my first pictures and these makes it easy to see how difficult it is to make accurate measurements with inexpensive testing equipment.

Karve SBD
View attachment 1279782
Karve OCD
View attachment 1279783

And to satisfy @Dovo1695, with greater magnification. The difference in heights of the side of the razor and the end of the blade makes it impossible to get both in focus at the same time, so I adjusted the focus in between.

Karve SBD
View attachment 1279784
Karve OCD
View attachment 1279785
I'm excited about those close ups! So excited in fact I decided to figure out how to use the ImageJ software, which took me a little while. The software isn't that complicated, but I'm not particularly bright. The reason that I decided to go with ImageJ is that I noticed some oddities in PowerPoint where the angle that a line segment is drawn at influenced the measured length of the segment. It was never designed for measuring small things. Measuring microscopic things is ImageJ's raison d'etre.

At any rate, here is my first attempt at taking measurements in ImageJ. It's really pretty straightforward software. Now I'm trying to figure out how to use the focus stacking functionality. That's less straightforward, but should double the accuracy.

The most important part of accuracy is repeatability. If I measure a gap of .97 vs an actual gap of .98, that's not really accuracy. It could be luck. If 5 people get the same measurement, now we've moved into the realm of repeatability. In all likelihood, there will be a range of values between .92 and 1.04 for example. The smaller that range, the higher the accuracy of the method being used. Anybody can do what I'm doing. ImageJ is free to use, and you don't even have to download it since there is a browser version.

As for the accuracy of these measurements, I'm pretty happy with it. I measured a gap of .97mm vs a stated 0.98mm and I measured an exposure of 0.10mm vs a stated 0.13mm. There is a lot of guesswork and interpretation involved, so if multiple people took these same measurements with these same photos, there would be a range of values.

 
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