Do-It-Yourself - AGGRESSION measured [Revised]

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

The following instructions are revised from the earlier post
and I hope easier to follow ...

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IDEA !!!
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If we could find a few razor owners who would calculate blade gap measurements to replicate/verify each other's results we can easily 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.
But ...
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 I have a photograph of the head of a razor - straght on looking "into the gap between the blade edge and the safety bar.

If I zoom in (or magnify it) by some factor I could increase the head's length on the screen to say 50 inches.
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 the gap appears, I can simply measure it - on the screen directly.

All double edge razor blades have a fixed length and must fit snuggly in the head of the razor.

* That space is 1.47 inches long and easily visible on a picture of the razor




If the gap is, for example 1 inch wide on the screen

I can now calculate the actual gap size by the following formula:

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THE FORMULA

Actual gap = 1.47 x gap measured on screen / blade length magnified

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

Step 1:
Take a picture of a razor straight on

Step 2:
Magnify that picture using a computer and display it on the screen (about 30-40x)

Step 3:
Measure the gap (now on screen it is aprox 3/4 of an inch)

Step 4:
Calculate the actual gap size from the formula

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What do you need?

a) ruler [12 - 15 inches] with markings of 1/16 of an inch and perhaps a 2nd one [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 or basic arithmetic ability


TIME REQUIRED:

AFTER YOU'VE DONE A FEW - is a matter of only a few minutes per razor.
The first few times through the process, however, will take a little longer.

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STEP 1: 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 (it's easier to see) - 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).

Tips:

- No flash is needed. 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.

- rotate the handle so the corners of the blade are at right angles to the line from the lens to the razor.

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

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STEP 2: Computer magnification

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

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

c) Make NOTE of the magnification factor needed to make the head size equal to about 30 - 50" on the screen

The exact way you do this depends on your camera's resolution and your computer software.

Typically the original shot needs to be reduced to fit on the screen say by 50% where the blade length space will appear to be say 12 inches.

To get the head up to a 36" inch magnification it must be increased 3x.
This would result in a "MAGNIFICATION FACTOR" of 6x

300% / 50% = 6x

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STEP 3: Measure the (6x magnified) gap on the screen


EXAMPLE:
9/16 inch = 0.5625 = 0.563 inch

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STEP 4: Calculate the actual size of the gap.

THE FORMULA

Actual gap = 1.47 x gap measured on screen / blade length magnified


1.47 x 0.563 / 36

= 0.0229891

= .023" +/- .001 inch

If you do everything right, the "gap" result - for any given safety razor - will be between 15 and 45 (1/1000's of an inch).


That's all there is to it.

After a few values are measured & calculated an average value is established and the razors can be ranked by blade gap size.

Instead why don't you just measure the gap with a feeler gauge?

cooncatbob said:

Instead why don't you just measure the gap with a feeler gauge?

Click to expand...

Seems like a good tool for the job ...
the commonly available ones are in the .002 - .025 range and
blade gaps are a little higher than that (.020 - .040)

There is no reason not to use a "feeler" type tool if you have one that spans the range required.

2bits said:

Seems like a good tool for the job ...
the commonly available ones are in the .002 - .025 range and
blade gaps are a little higher than that (.020 - .040)

There is no reason not to use a "feeler" type tool if you have one that spans the range required.

Click to expand...

You can stack them to measure larger gaps.

cooncatbob said:

You can stack them to measure larger gaps.

Click to expand...

I don't have access to feeler guages but if anyone has such tools it would be interesting to confirm measurement made by other methods.

Seems it would only take a minute or two to get some value for a give razor.

Anyone able to try this?

I just used my feeler gauges to measure my new Progress. At a setting just to the right of 1 on the dial, I measured 25 on the left side of the blade. Now, here's where it gets interesting. . .

At that same setting, on the right side, I measured 40. I'm no razor scientist but I'm pretty sure that is not within acceptable tolerances for the Progress. Looks like I get to have a chat the store I bought it from.

BeansBaxter said:

I just used my feeler gauges to measure my new Progress. At a setting just to the right of 1 on the dial, I measured 25 on the left side of the blade. Now, here's where it gets interesting. . .

At that same setting, on the right side, I measured 40. I'm no razor scientist but I'm pretty sure that is not within acceptable tolerances for the Progress. Looks like I get to have a chat the store I bought it from.

Click to expand...

Sounds like a collectors item ... the first adjustable slant.

Yikes.

But seriously good to know so you don't go nuts trying to figure how to steer the thing.

2bits said:

But seriously good to know so you don't go nuts trying to figure how to steer the thing.

Click to expand...

Steer the thing?
I'm not even going to get behind the wheel of it!

This baby is going back home to Deutschland for some remedial training. . .

I like the idea of ranking the "aggressiveness" of razors by looking at blade gap and angles (http://badgerandblade.com/vb/showthread.php?p=582199#post582199):)

Here are my thoughts:

In my opinion, the aggressiveness of a razor is determined by the steepest angle that the design allows between blade edge and skin.

Here is how I would measure it:



First, construct the plane defined by the blade edge and the guard. This plane is viewed edge-on in the above diagram and is thus represented by a line (black). Second, estimate the direction of the blade edge (blue line). The steepest angle is defined as the angle between these two planes.

I have drawn two scenarios that differ only by the vertical distance between the blade and the guard as is found on most adjustable razors.

I think this is the best way to measure the gap and is preferable to the "head-on method" proposed by 2bits. (Just to make sure: this is not meant as a confrontation; it's a scientific discussion ). The reason is illustrated here:



Two razors are shown, one where the guard protrudes quite significantly from underneath the blade (A), and one where the guard edge is practically right underneath the blade edge (B). Using the "head-on" method, the gap on both razors would come out to be the same, but they clearly differ - and not only in their blade gap, but also in their aggressiveness.

In the first diagram, it is immediately clear why an adjustable razor results in a more aggressive shave when the gap is increased: the angle increases.

So much for now.

Best - MM

mozart said:

I like the idea of ranking the "aggressiveness" of razors by looking at blade gap and angles ... the aggressiveness of a razor is determined by the steepest angle that the design allows between blade edge and skin.
... I think this is the best way to measure the gap and is preferable to the "head-on method"

Click to expand...

Great stuff and good to come at this time for I can (soon) try with a variety of razors to keep the shot dead on the blade edge and see if I get consistent (more precise) results that more closely mirror experience.

I can easily redo some measurements and hopefully the method will enable the difference between adjustables and others to be established
- if not another approach
- maybe even a side angle shot - tricky but there might be a way to measure angles.

I think all this is going to be fun and do-able.

Thanks for the brain work ...
we're on the right track I'm sure

Later

A "Feeler" gauge, should really be the name of the largest most deadly shot-gun ever made.
Whenever I hear that word, it just does not sound like a measurement tool...

2bits said:

Great stuff and good to come at this time for I can (soon) try with a variety of razors to keep the shot dead on the blade edge and see if I get consistent (more precise) results that more closely mirror experience.

I can easily redo some measurements and hopefully the method will enable the difference between adjustables and others to be established
- if not another approach
- maybe even a side angle shot - tricky but there might be a way to measure angles.

I think all this is going to be fun and do-able.

Thanks for the brain work ...
we're on the right track I'm sure

Later

Click to expand...

Great! Unfortunately, I don't have the equipment to take proper side-view macro shots of razors, which would be what's required. If you can do that, that would be fantastic.

It doesn't get any geekier than that...

Best - MM

mozart said:

Great! Unfortunately, I don't have the equipment to take proper side-view macro shots of razors, which would be what's required. If you can do that, that would be fantastic.

It doesn't get any geekier than that...

Best - MM

Click to expand...

I know these 2 razor models are not the best to compare but it is what I have on hand ...

I measured the angles (protractor against screen and my eyeballs such as they are) as you suggested - degrees formed at blade edge between blade and the top of the safety bar

the results were

Gillette tech - 25 degrees
Feather portable - 30 degrees

This is not too different than the RATIO of the gaps measured straight on

Gillette tech - .023"
Feather portable - .029"

(*** probably as the designs are so much alike)

anyway here are the pics

Method:
- hand held (1 for razor & 1 for camera)
- light background at distance of 2-3 feet
- light of day from behind
- camera set for closest focus
- position distance to get as big as possible and sharp (2-3")
- no macro lens used - lens set at eqiv 28 (camera has a zoom lens eqiv 28 - 300)
- I used the view finder (not lcd screen)
* I steadied the razor by touching the front of the lens with the hand holding the razor

Click / done / no problemo

All computer stuff in Linux so won't apply to MS users.

Oriented the shots to match your diagrams for easier comparison.

I think you're calculation for error is incorrect. The most accurate measurement you can make with a ruler with 1/16" intervals would have an error +/- .03125. For a ruler with 1/32" intervals that number becomes +/- .01563.

We multiple measurements (each of which has an error) according to the formula you present: Actual gap = 1.47 x gap measured on screen / blade length magnified

Since we multiply measurements that have been measured with the ruler, the errors increase. All I'm trying to say is that the error in these calculations are much greater than +/- .001 in, at least one order of magnitude. I based my assumptions on that there are two, one for the razor on screen and the other for in space, but the magnification factor (1.47 in your example) has an error associated with it too, but I am not certain to how to calculate that, but it would further increase the error. I haven't actually calculated the errors, but if you're interested, do a search for error propagation on Google or the likes.

With this in mind, I don't think it is worthwhile to measure blade aggressive in this way because the amount of error is relatively close to the size of the measurement itself. The amount of error in these calculations would be too unreliable to use this as a reference.

DarkDragon786 said:

I think you're calculation for error is incorrect. The most accurate measurement you can make with a ruler with 1/16" intervals would have an error +/- .03125. For a ruler with 1/32" intervals that number becomes +/- .01563.

Click to expand...

The measurements made with a ruler marked in 1/64 if an inch can be estimated to 1/128 or .008". This was not how the measurements were made however.

The razor blade length 1.470 was made with calipers and is accurate to .001"

DarkDragon786 said:

... Since we multiply measurements that have been measured with the ruler, the errors increase.

Click to expand...

The calculation is singular and so the accuracy can be no better than the least accurate factor in the calculation.

DarkDragon786 said:

... the magnification factor (1.47 in your example) has an error associated with it too, but I am not certain to how to calculate that, but it would further increase the error.

Click to expand...

The magnification factor is not 1.47. The magnification factor ranged from 25x - 50x and rather divides the other factors as the reason for using a magnification is to reduce the error. Typical range for the magnification was 25 - 50x so if screen ruler measurements were made to 1/32 which is easy the measurement error is .00125 to .000625.

Accuracy:
blade length .001
gap .00125 to .000625

The calculation can not be more accurate then the least accurate if these

ie .001"

DarkDragon786 said:

I don't think it is worthwhile to measure blade aggressive in this way because the amount of error is relatively close to the size of the measurement itself. The amount of error in these calculations would be too unreliable to use this as a reference.

Click to expand...

Multiple measurement and calculations were done by different people using different cameras and computers on different samples of the same model razors and using different measurement methods (rulers and feeler gauges).

While there was a range of results of +/- .002" there were multiple results that agreed to .001" for a given model.

The requirement to rank the razors by gap size need be no better than +/- .002". With averaging of the results it is easy with a few samples to see which models are "one setting higher/functionally equal/or lower than an other.

The final check is that the derived ranking agrees (so far without exception) with the subjective reports of many different users.


The original assertion was that the gap would be measured to +/- 0.001"
Even if that is not the case (and that might be so for a single data element). Unless it was the only data element and in error by more than .004" it would have no impact on the ranking in any case.

Looking at it another way ....

If you

1) took a penny (thickness of .052") and set it against the edge of the blade and resting on the safety bar of the razor.

2) Photographed the coin (on edge) so you could see how far up the side of the coin was the cutting edge of the blade touching.

3) magnified the picture so the coin looked to be about 1 - 2" thick you could measure the gap well enough to rank the razors.

It's very helpful to have folks paying attention.

Thank you for that.

2bits said:

The measurements made with a ruler marked in 1/64 if an inch can be estimated to 1/128 or .008". This was not how the measurements were made however.

The razor blade length 1.470 was made with calipers and is accurate to .001"

Click to expand...

From your initial post, I was under the impression that the measurements were made with a ruler with 1/32 or 1/16 markings, so the calipers significantly improve the accuracy.

2bits said:

The calculation is singular and so the accuracy can be no better than the least accurate factor in the calculation.

Click to expand...

Correct, but it will be less accurate the least factor.


Source: http://phoenix.phys.clemson.edu/tutorials/errorp/index.html

The two independently acquired measurements (where x and y are the gap and length measurements) are divided to calculate the actual gap, so the new error follows the formula in the division row of the table above.

Then again, it might not matter when using precise feeler gauge, but the final error is greater than the errors of any of the measured quantities. I will revise my opinion on the ranking method because if the measurements are done with accurate tools, confirmed by measurements from other users, then compared with subjective comparisons, then the procedure is rigorous enough to guarantee accurate results.

DarkDragon786 said:

... I don't think it is worthwhile to measure blade aggressive in this way because the amount of error is relatively close to the size of the measurement itself ...

Click to expand...

Set your razor on 5 and place an American penny so the blade touches the edge of the coin at 90 degrees and the side of the coin lies flat on the safety bar.

If your eyes are better than mine you can see the blade is touching approximately 1/2 way up or 50% of the coins thickness.

I think a penny is between .050 and .060" thick so just with the naked eye (no magnification) we could ball park the gap set at 5 to be about 1/2 of the penny or .025 to .030 (I forget exactly) .

The gap table average - so far - puts the value is .026

We can measure by eye to +/- .010 easy.

If the error factor was nearly as big as the value measured it would have to be about .025"


What is not within .001" is the manufacturing tolerances of razor makers.

I'm old a feeble, have bad eyes and a short term memory of 15 seconds and a working memory of "zip all"

I have to do things 6 times to get 2 results the same!

(Long term memory is fair to good though)

I love to learn so thanks for caring as much about the how and why as the final answer.

Keep that up and you'll be giving as good as you get around here.

And there's a lot of good to be got.

When we're not paying attention we're nowhere!

Happy to see you're here.

Thanks for appreciating the criticism, not every does. Your responses were well-reasoned as well. I hope I have contributed to developing this technique to compare different razors.

Good luck