Do-It-Yourself - AGGRESSION measured to +/- 0.001 inch

[2bits]

The following instructions will enable you to measure the blade gap of any typical safety razor to an accuracy of +/- .001 inch.

These are the results - so far -

=============================================
LIST A [last updated - 04/24/08]
=============================================

GAP in 1/1000's of an inch [ +/- .001 inch ]
new value
15 [.38mm]
16 [.41mm]
17 [.43mm]
18 [.46mm]
19 [.48mm] Ming Sui
20 [.51mm]
21 [.53mm]
22 [.56mm]
23 [.58mm] Gillette TECH
24 [.61mm]
25 [.64mm] Gillette NEW
26 [.66mm] SS Red Tip
27 [.69mm] US & English ARISTOCRATs
28 [.71mm]
29 [.74mm] Feather Portable
30 [.76mm]
31 [.79mm]
32 [.81mm]
33 [.84mm]
34 [.86mm]
35 [.89mm]
36 [.91mm] Slim Adjustable @ 7
37 [.94mm]
38 [.97mm]
39 [.99mm]
40 [1.02mm]

========================================


[I'm sorry this post turned out to be a little on the - l o n g s i d e - it will take about 7-8 minutes to read. The process described is much more simple than it appears and in practice you can determine the gap of a razor in less time than it takes to read these instructions.]

Question:
Why would anyone care what the measurement of a razor's blade gap is?

Answer:
If you know their blade gap sizes you can rank razors more precisely by what is often referred to as "aggression".

Being able to compare the "aggression" of various razors, you could then make more reasoned adjustments in shaving technique and better choices when selecting a razor.

&
=================
IDEA !!!
=================

If we could find a few
"computer & camera cowboys" with "big razor ranches",
(who were looking for an excuse to play with their toys),
we could get blade gap measurements replicated/verified
and create a comprehensive table of relative blade gap measurements.

=============================

Background:

Here's the trick ...

Imagine I have a photograph showing myself standing by a tree.
My image, in the picture, measures only 1 inch (head to foot).
The tree, in the picture, is 2 inches from it's highest branch to the ground.
I know my "actual" height is 6 feet.
Since the tree, in the picture, is 2 inches = 2x taller than me, in the picture,
the tree must be 2x6 feet in reality or 12 feet tall.

Now imagine that same photograph is on my computer screen and I zoom in (or magnify it) by a factor of 72.
Because everything in the picture is now 72 times bigger - my on screen height now appears to be 72 x 1 inch or "actual life size" (6 feet head to foot).

My image is now much too big to be contained entirely on the screen but if I scroll to the part of the image where my belt appears, I could measure it on the screen "directly".

If my belt is 1 inch wide on the screen, I know the belt I was wearing when the picture was taken was 1 inch wide.

This is the trick that makes it possible to measure the blade gap of any safety razor.


If you measure a razor's safety bar and it is say 1.5 inches long and you take a picture of that razor straight on, you can magnify that picture using a computer and display it on the screen.

If you magnify the image such that the head of the razor almost fills the screen the safety bar will appear to be about 12 inches long (x8 larger).
The blade gap then will then be less than 1/4 inch (too small to measure accurately).
If you further magnify the image another 4 times the safety bar is now 8x4 = 32 times larger.
[32 x 1.5 inches = 48 inches]

The head of the razor, on the screen, will appear as if it were 4 feet long and the gap on the screen will be almost 1 inch wide. That gap is now easily measured with some precision.

The "on screen gap" measurement
divided by the magnification
is the actual razor gap size.

=====

So how do I do it? you ask ...


To determine the blade gap of a razor - the steps are 4 and all fairly "easy":

1) Measure the length of the safety bar of the razor.
2) Take a photograph of the razor.
3) Using a computer and a photo manipulation program, measure a "magnified" image of the safety bar and the gap on the screen.
4) Calculate the actual size of the gap.


What do I need?

a) 2 rulers,
- one long enough to measure the width of your screen [12 - 15 inches] with markings of 1/16 of an inch
- a second ruler [6 inches] with finer markings of 1/32 of an inch.

b) a digital camera that can focus on an object "close up" at a distance if less than 8 inches from the lens

c) a computer with software that can zoom in and out to resize your photo on screen

d) a calculator


TIME REQUIRED:

To calculate the gap of a single razor - AFTER YOU'VE DONE A FEW - is a matter of only a few minutes.

The first few times through the process, however, will take a little longer.


["EXAMPLE:" measurement values that follow are of a newer sample Gillette TECH safety razor]

=========
STEP 1: Measure the safety bar of the razor and convert that length to thousandth's of an inch.
=========

With a ruler measure the safety bar of the razor to an accuracy of at least 1/32 inch. (You can use calipers if you have them but it is not required). The result will typically be a little greater than 1 1/2 inches.






EXAMPLE:
a Gillette TECH's safety bar is measured to be ... 1 and 39/64 inches long so it is 1.609 inches long
(39 divided by 64 = 0.609375 plus 1 inch = 1.609)

*** This is value La = 1.609 inch ***

Tip: Fractions of an inch in 1/1000's are easy - with a calculator ...
1/64 = 1 divided by 64 = 0.0156 = 0.016
1/32 = 1 divided by 32 = 0.03125 = 0.031
1/16 = 1 divided by 16 = 0.0625 = 0.063
1/8 = 1 divided by 8 = 0.125
5/32 = 5 divided by 32 = 0.15625 = 0.156
39/64 = 39 divided by 64 = 0.609375 = 0.609
etc ...


=========
STEP 2: Take a digital photo of the razor.
=========

I hold the camera with my right hand and the razor in my left and found no tripod was required if there was bright daylight (or even normal artificial light available).

Take a picture of the razor WITH A BLADE INSERTED - as close to the lens as your camera can focus - so the head of the razor is as big as possible (but still remains completely contained in the picture).

At a distance of 12 inches or more the razor's image will probably be too small for good results ...



The picture above was taken with the razor about 12 inches from the camera.

You can see that with a 5x magnification the gap is not big enough to me measured with precision.

Try to get a picture more like this ...



The above was taken at a distance of 4 inches and the razor head takes up a much greater portion of the picture.

At 5x magnification, the gap is now much easier to see and measure.

Tips:
- No flash is used. Natural daylight is best and should come from behind you.

- Try to get the camera to look directly into the gap between the blade and the safety bar.
The difference between the razor being perfectly vertical (top of blade slightly visible) or tilted slightly away from the camera (so only the blade edge is seen) makes less than a 0.001 inch difference and will not significantly effect the final results.

- take several shots so you increase your chance of getting a good sharp "straight on" result


=========
STEP 3: Computer magnification and on screen measurement of safety bar and gap.
=========

Upload your pictures from your camera to the computer and then ...

a) select the best - sharpest - shot looking "straight on" the razor gap.



The above picture shows the advantage of lighting coming from behind.

With magnification - even when the lighting is not ideal - the gap is easily measured.


b) zoom or resize your best pic - such that the razor head is as big as posssible on the screen yet remains completely visible.

Measure the safety bar "on screen" length



EXAMPLE:
Safety bar on screen = 12 1/4 inches = 12.250 inches

*** This is value Lb = 12.250 inch ***


c) Make NOTE of the reduction/magnification factor used in previous step b). It may range from 25% to 200% depending on your camera, computer screen and software.

EXAMPLE:
150%

*** This is value Ma = 150% ***

d) zoom or resize the screen image upward so the blade gap about 3/4 to 1 inch.

Tip: Use simple multiples to make it easier to calculate the magnification factor.

Make NOTE of the magnification factor used.

EXAMPLE:
450%

*** This is value Mb = 450% ***

If the original shot is zoomed up by 150% as in c) to get razor head all on screen and then further zoomed up to 450% in d) to enlarge the blade gap for measuring this would result in a "MAGNIFICATION FACTOR" of 3x

[Mb / Ma]

450 / 150 = 3

*** This is value Mc = 3 ***

e) measure the gap on the screen and express it to 1/1000ths of an inch

EXAMPLE:
9/16 inch = 0.5625 = 0.563 inch

*** This is value Ga = 0.563 inch ***


=========
STEP 4: Finally - Calculate the actual size of the gap.
=========

You're nearly done!

a) first calculate the size of the magnified safety bar

Multiply the MAGNIFICATION FACTOR [Mc] from Step 3d
x
the on screen safety bar measurement [Lb] from Step 3b

EXAMPLE: Mc x Lb

3 x 12.250 = 36.75 inches

*** This is value Lc = 36.75 inches ***

b) The "Payoff"

Calculate the actual gap size

Multiply the actual safety bar length from Step 1
x
the on screen magnified gap measurement from Step 3e
then divide by the "magnified screen" safety bar length from Step 4a

La x Ga / Lc

EXAMPLE:
1.609 x 0.563 / 36.75

Final calculated result = 0.0246494

so ...

the ACTUAL BLADE GAP is 0.025 inches +/- .001 inch

==================================

If you do everything right, the "gap" result - for any given safety razor - will be between 15 and 50 (1/1000's of an inch) and probably "close" to the values in the LIST B below.

==================================

Here is the tentative start (LIST A) of what I hope will become a comprehensive list of MEASURED razor gaps.
I currently have access to only 6 razors and LIST A contains my results using the method described in this post.

As you can see I could use some help filling in the "gaps"

A very generous forum member who lives nearby has offered to lend to me some razors from his collection for measurement and photographing so "stay tuned".

With a little luck this information will be updated soon.


=======
LIST A [last updated - 04/24/08] *** SEE CURRENT UPDATED VALUES AT THE START OF THIS POST ***
=======

GAP in 1/1000's of an inch [ +/- .001 inch ]

15
16
17
18
19 Ming Sui
20
21
22
23 Gillette TECH
24
25 Gillette NEW
26 SS Red Tip
27 US & English ARISTOCRATs
28
29 Feather Portable
30
31
32
33
34
35
36 Slim Adjustable @ 7
37
38
39
40

=================

The next data (LIST B) was compiled from a survey of comments and "subjective" comparisons posted on this and other shaving forums.

*** Note: These are only "GUESS-timates" and while they may be useful as a guide to indicate that a measurement is "in the ball park" they NEED TO BE VERIFIED by actual measurement ***

======
LIST B [last updated - 04/23/08]
======

ESTIMATED
GAP in 1/1000's of an inch [ +/- .001 inch ]

15
16 Gillette ADJUSTABLE @ 1
17
18
19 Gillette ADJUSTABLE @ 2, Weishi, Ming Sui
20
21
22 Gillette ADJUSTABLE @ 3
23 Gillette TECH, Star
24 SS BLUE Tip, Merkur HD/38C
25 Gillette ADJUSTABLE @ 4, Gillette NEW
26 SS SILVER/TAN Tip, Gillette OLD "BIG FELLOW"
27 US & English ARISTOCRATs
28 Gillette ADJUSTABLE @ 5, Gillette "Old" TECH, PRESIDENT, 58TV SPECIAL
29 Feather Portable
30 SS RED Tip
31 Gillette ADJUSTABLE @ 6
32 Gillette "New Improved", Parker 22r
33
34 Gillette ADJUSTABLE @ 7
35
36
37 Gillette ADJUSTABLE @ 8
38
39
40 Gillette ADJUSTABLE @ 9, Merkur FUTUR @ 6

=================

Additional razors of interrest that might be added to the above lists:

Merkur 1904, PROGRESS & VISION, SLANT etc
Feather Popular
Shicks
Lords
Parkers
misc. "Disposable" razors
injectors
antiques
etc etc etc ...

[BJC]

2bits,
I think you proposed idea is a good one. A more accurate (measured) ranking of razors in terms of aggressiveness would be useful for comparing and considering razors. I might be able to add a few to the list is time permits next week. Thanks again for the idea.

BJC

[kestrel]

2bit

This sounds like an interesting idea; essentially, if you establish the size of the razor head relative to the picture of the razor head by means of measuring the bar, you can then discover the size of the blade gap by measuring the picture of the blade gap.

Have I got it right?

Graham

[scoopster]

This is a very interesting, well written read and a great way to benchmark the aggressiveness of razors. Nice job!

One thing that popped into my head is that this seems like a very accurate way to benchmark razors against each other but may not measure the "true" gap. I'm assuming the photos are of the razors at a perfect 90 degree angle to the camera. I think the true blade gap might be different as the real opening distance needs to be determined based on the perpendicular distance between the blade, which is curved, and where that measurement line intersects the safety bar (which also has some complex geometry). That true opening distance is not necessarily going to be "seen" looking at the razor from a 90degree/side view.

To see how accurate this approach is I think measuring the true gap with a machinists tool would confirm whether the technique produces a difference in results. And again, as long as the same measurement approach is taken, it really doesn't matter, there is a lot of value in being able to accuratly compare the aggressiveness of these razors with some common measurement system.

Again, nice post!

[ateace]

This is a great idea - I'm surprised that this hasn't been done before.

My approach is more crude. If I can slice coldcuts with my adjustable, I dial it down!

[Radar O\'Reilly]

The question I have is do the measurements differ with different blades? If a blade is wider than another, than it's edge would be closer to the bar as it curves down, which would alter it's angle of attack, right?

[2bits]

2bit

This sounds like an interesting idea; essentially, if you establish the size of the razor head relative to the picture of the razor head by means of measuring the bar, you can then discover the size of the blade gap by measuring the picture of the blade gap.

Have I got it right?

Graham

I could have saved several screens of blather by saying it exactly that way!



Thanks Graham

[2bits]

This is a very interesting, well written read and a great way to benchmark the aggressiveness of razors. Nice job!

One thing that popped into my head is that this seems like a very accurate way to benchmark razors against each other but may not measure the "true" gap. I'm assuming the photos are of the razors at a perfect 90 degree angle to the camera. I think the true blade gap might be different as the real opening distance needs to be determined based on the perpendicular distance between the blade, which is curved, and where that measurement line intersects the safety bar (which also has some complex geometry). That true opening distance is not necessarily going to be "seen" looking at the razor from a 90degree/side view.

To see how accurate this approach is I think measuring the true gap with a machinists tool would confirm whether the technique produces a difference in results. And again, as long as the same measurement approach is taken, it really doesn't matter, there is a lot of value in being able to accuratly compare the aggressiveness of these razors with some common measurement system.

Again, nice post!

Re: precision question ...

What I found was
- the width of the blade differing by manufacturer
- blade bending amount
- the blade edge "dead on" vs razor tilted & foreshortening of the gap
- rotation of handle leading to foreshortening of the safety bar length measurement

... all these change the numbers and the "measured" outcome
BUT
the range of error was usually less than .001 and even in combination less than .002
AND
if the main objective is
NOT to establish the number to higher accuracy ie .000001"
BUT
to be able to RANK the razors as
MORE or LESS aggressive than each other
OR
"functionally" EQUAL

If we get a few measurements
from a few sources
and they agree within a range or +/- .003"
my suspicion is that we will have the RANKING
as accurate as the differences in a
single setting variation of a Gillette adjustable
and be CLOSE ENOUGH FOR ROCK an ROLL


re: alternate measuring methods ...

Great - the more methods and the more data means the better the ranking will be.

We can throw out the extreem results (HIGH/LOW) when we get a few that "cluster" around the probable manufacturer's intended gap size.

re: variation question ...

The gap varies from point to point along the head of a single razor (they are "tucked in at the ends" on some Gillette's for instance) and I suspect they vary with manufacturing quality control or if the razor has been subject to damage etc.

The trick is to get the data to "cluster" around a value that makes the ranking of the razor possible for some practical purpose.


I suspect, the LIST B ranking, based upon completely anecdotal reports by users, with no "measurement" at all will be confirmed, for the most part, correct. If that is so, it will be the verification that "multi-methods" that drop the "fringe" results is enough to "point" accurately at the true value on average. Even if we had a few very precise measurements, however precise, they would be rounded and placed in a "box" that is +/- .003" in the end.

[DanOK]

Thank you for a most enjoyable read. I have been searching for a criteria to use in evaluating razors and your efforts provide a fascinating approach to developing a standard which is straight forward and easily replicated. I know all of us are looking for some constance standard that could be applied across manufactures and models to rate razors. As noted above "a way to benchmark razors against each other".

I know I'm addicted because I on longer travel the interstates but use the back roads and by-ways in fear I will miss the next little shop that has a 50 cent Fatboy.

[Prince]

This is a great idea - I'm surprised that this hasn't been done before.

My approach is more crude. If I can slice coldcuts with my adjustable, I dial it down!

That's too funny.

[DanOK]

As a side note thank you for keeping the unit of measure old school as its the language I learned in my youth and the language I continue to use in all the engineering projects around my castle.

[2bits]

... I might be able to add a few to the list is time permits next week. ...

BJC

If we can get a few numbers for the common razors even a system of simple averaging will soon point to a stable value for that model.

Any data will be a help.

Thanks for your support.

[2bits]

... thank you for keeping the unit of measure old school as its the language I learned in my youth and the language I continue to use in all the engineering projects around my castle.

I'm a bit of an "old fart" myself and prefer the inches, pounds, and quarts measures of the world around me.

It fits a little better with the project too as it is really not "accurate to .001" in the way "metric micrometer" might suggest.

The final list ranking at best will be a relative average derived from several more "accurate" measurements.

It will be a learning point for some to realize the gap measurements on a single razor vary from point to point and a "true" single measurement is a phantom. The manufacturing precision of razors is certainly less than .001"

A stable average value is both easy to determine and may be useful even if there is not a single example razor that measures exactly "average".

Thanks for the kind remarks

[rabidpotatochip]

Very interesting read. Though I admit I originally came into this thread because I thought it was a story about a home renovation project...

[2bits]

Need advice on best / easiest / simple method to "AVERAGE" measurements from a variety of sources.

?

- simply average all data points?
- drop highest & lowest and average the rest?
- drop all outside a reasonable range ( +/- .003" ?) ?
- a value is "the one" when there's no change (or no more data forthcoming) ?
- when data "trend line" varies by < .002" the value is optimum ?
- that's the number and you can cry if you want to ?

?


Any thoughts from the wiz kids would be welcome

Take your time, (aka argue among yourselves / smoke if you got em')

[rabidpotatochip]

My wife said I was average, but I think she was being mean.

[Mr. Gillette]

I came to the thread because I thought it was about aggressive behavior-- but (all kidding aside) It's something to think about. Aggression (to me) is easily "measured" by how many microns of skin come off when I drag it across my face---

But cataloging it and quantifiying it ahead of time is, indeed interesting.

THANKS!!!! I'll try it with a few of my treasured razors.

[2bits]

My wife said I was average, but I think she was being mean.

Some guys like it a little "rough".

[2bits]

... I'm surprised that this hasn't been done before.

When all is said and done -
more will be said than done.

- Curly Larry or Moe

... My approach is more crude. If I can slice coldcuts with my adjustable, I dial it down!

It is a wise man who focused on the here and now (hear and know?).

[Haiku]

Brilliant idea, and well put together. A very enjoyable and enlightening read. Thanks for taking the time and making the effort to post this for us.

I have one problem though and that relates to optical distortions.

In order for the measurement to be accurate, you need to know that the lens does not distort the ultimate image. Unfortunately, even with the best macro lenses, you will get distortion and the measurements will be off. The more the magnification, the greater the problem will be magnified.

The (partial) solution is simple though. You need to correct the distortion. I suspect that the easiest way to do that is to measure the image of the ruler on the screen. If the measurements of the ruler are accurate, then the rest of the image in the same plane of critical focus as the ruler will also be accurate. Note that the correction will only work for items in the same plane of critical focus as the ruler. Accordingly, I suggest that you use as small an aperture as available, but even then, the ruler and the razor must be as close to one another as possible. For this, an accurate tripod and accurate measurements lens to subject will be crucial.