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pressure

Posted by fervens 
pressure
April 04, 2015 04:49PM
So i had an idea to show how much pressure i use to other people on the interent. Scales are a little annoying to mess with while sharpening. So what i did was go a no.2 pencil and some printer paper and started shading the paper. Starting with a lot of pressure at one end and ending with as little as i could manage at the other. This was my result.



If i keep a pencil and some paper near me when sharpening, i can do a quick test to see the amount of pressure i'm using, when. I started doing this after seeing Cliff's video on his soft Arkansas.

Things i could do to improve this method is:

-Wrap the paper around a stone and hold the stone in my off hand, then hold the pencil similar to a knife.

-Put the paper on a scale so i can have a starting idea of how much pressure is used when.

- Roll the pencil while shading. I noticed if i don't pay attention i will either not roll to randomly roll the pencil. this would cause the shading to darken or lighten depend on which side of the lead i was using. if i stayed only on one side, then a large flat facet would form and it would look like i was using less pressure when i wasn't or vise versa.
Re: pressure
April 04, 2015 05:33PM
To start, before anything else, any measurement you make, any attempt at quantification is better than doing nothing.

In sharpening, it isn't the force you apply, it is the pressure. This is why you not only need to look at how much force you apply but the contact area on the blade. For example on a typical western knife :

-1 lbs applied, bevel is 1/32" wide, contact area is 1" long = pressure of ~32 psi

Typical Japanese knife :

-10 lbs applied, bevel is 1" wide, contact area is 3" long = pressure of ~3 psi

This is why Japanese and Western stones tend to be so different in strength.
Re: pressure
April 04, 2015 05:54PM
I do realize the point you are trying to make, Cliff. I even elude the same effect happening with the pencil and shading. Using the different facets. Using the same force but different sides of the pencil lead (one pointy and one flat) you will get a good idea of this effect. Just by looking at how dark of a mark the point left compared the the flat.

Quote
fervens
- Roll the pencil while shading. I noticed if i don't pay attention i will either not roll to randomly roll the pencil. this would cause the shading to darken or lighten depend on which side of the lead i was using. if i stayed only on one side, then a large flat facet would form and it would look like i was using less pressure when i wasn't or vise versa.

The soul purpose of this was to provide a way of visualizing the amount of force a person is using while sharpening. Numbers are not always as meaningful as their true value. Any one can do a quick shading with a no.2 pencil using high to low force and be able to visualize how much force the person in the video (or thread) used. No scales needed. One can also show the bevels being sharpened to allow the viewer(reader) to ball park the pressure.

I also found that doing this exercise helped me realize the defference even a small change in surface area can make.
Re: pressure
April 09, 2015 12:27PM
I think this is brilliant. Maybe try putting the paper on the scale and take readings of how hard you are pushing using the pencil, and also form the pencil tip to a specific measurement for consistency, as Cliff pointed out the affects of force vs. pressure. How about also a do an outline to follow to make and use this, so someone could then have their own pressure gauge, because this can be such a subjective issue when talking about using light preasure, a lot of pressure, ect., this at least can allow for individual reflection to their sence of touch and use if force.

"I am still discussing issues of steels and performance at this stage."
--Cliff Stamp

"Cause geometry cuts, .....steel determines the level and the duration"
--Roman Landes

"But in general, I'm all about high performance, Ergos, safety. That's why I've been accused of 'designing in the dark' "
--Sal Glesser
Re: pressure
April 10, 2015 11:45AM
Pretty much all of that. I find it helpful to recalibrate myself. And maybe at some point i'll do a write up on shading with pencil and how the surface area of the lead can effect the shading just as much as the force used.
Re: pressure
April 12, 2015 03:04PM
Great! I think that this a wonderful idea that you came up with and can be very helpful!
Re: pressure
May 05, 2015 12:21PM
I had been thinking about how to get a description of how someone can get an idea of what a lightweight touch on the stones. I had tried just using the thumb in forefinger only, to give someone an example of what a light touch is if they are heavy handed or just might be using too much pressure when it isn't desired. The problem I found with using only the thumb and forefinger is that it is hard to maintain proper control of the angle of the knife on the stone, so what I came up with is a three finger hold im a pinch grip, with the index finger extended along the spine of the blade to the tip of the knife for balance, and the thumb and middle finger holding the handle.
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