Abrasives and edges

[Herman Trivilino]

I experience exactly that also.....can bring back a not too far gone chisel or plane edge with the strop.....I'm not even going to ask whats going on there at the microscopic level because in theory that shouldn't work right??

I think it's sort of the same thing as using a steel on a knife.  Theories are based on models, and so are only as good as the model.

The classic example is the traffic engineer and the car mechanic.  The traffic engineer models a car as a moving dot on his map.  No need to be concerned with the details of how the car makes itself move.  Such a model could never be used by the mechanic as he needs very much to be concerned with the details of how the car makes itself move, and stop!

[Herman Trivilino]

After that Canadian article which completely contradicts all of this, I have to say I was confused about what was going on. 

I guess I've lost track of the conversation here as I can't recall the Canadian article.

But following up on the modelling process, when we're grinding an edge we model the steel as a homogeneous material that needs to be shaped in such a way that two surfaces meet at a line.

When we zoom in on that line we find that it's not really a line at all.  The steel is so thin there that the crystalline structure of the steel is apparent.  That line is not straight but jagged.  And as Jeff points out it folds over and it crumbles. 

When we're grinding the edge we don't care about the crystalline structure of the steel.  We just try to get the geometry right and hope that the metallurgist did his job correctly and provided us with steel of the correct properties to actually form and hold an edge.

You can think of one of these models as being macroscopic and the other microscopic.  The modelling process itself is inherently flawed, but the proof is in the pudding.  If the model is good enough then the engineers who use it will be successful when they design tools with cutting edges and the machines that can sharpen them.

[Rob]

right...I think :-)

How many degrees do you have Herman?

[mike40]

It seems to me Herman that you are implying that theory is indeed theory and not fact. When a theory becomes proven it is then fact and no longer theory. Another problem with theories is that they often don't t take into account all of the variables, and therefore never become fact. In this case the breakdown of larger particles into smaller particles in stropping paste is a variable.  Also as you mention, the steel quality may vary and in my total ignorance of the subject, there might be other variables too, such as time, pressure exerted, water quality in the trough, the condition of the stone and stropping wheel, etc, etc. After reading the Tormek manual and seeing the relative pressure between wide and narrow blades, I would think pressure exerted might be a more important part of the sharpening/stropping equation than one might think. So where does this leave us? My best guess is trial and error with our particular tools instead of quasi scientific analysis.

[grepper]

From Herman's reply:

Quote from: Rob on Yesterday at 10:01:56 am
After that Canadian article which completely contradicts all of this, I have to say I was confused about what was going on.
-----------

Apparently the Canadian article caused some confusion; hopefully this will help clarify what he was actually saying.  Early in the article he states:

"This page is actually concerned with stropping of plane irons after a final honing step using a 0.5 micron abrasive."

He was sharpening, using 0.5 micron 3M Microfinishing Film.  The important thing to notice is that 0.5 micron size.  The Tormek Honing compound is, according to Jeff, comprised of equal parts of 1, 2, and 3 micron abrasives, and most other honing compounds a comprised much coarser abrasives than that.

Even the smallest abrasive in the Tormek Honing Compound is 2X more coarse then what he originally sharpened to.

So, he is only saying, that:  If you sharpen to 0.5 microns, using any of the honing compounds that he tested results in a degradation of the edge.

Is useful to know?  To me, yes.  I now have a much better understanding of exactly what stropping with various grit levels of stropping compounds means. 

Folks talk about how they really like the white crayon, or some like the black compound, etc.  Well, what grit level is it?  What grit level did I sharpen to?  How should a particular honing compound effect the edge? 

I find those questions to be interesting, and it's useful to be able to hazard an educated guess.

[Rob]

right...so all we can reasonably conclude is that if you sharpen to a grit size that's smaller than that in your stropping paste.....its a waste of time stropping because your strop is essentially worsening the edge with the less refined grit.

In the case of us and the Tormek, that doesn't hold true because at the 1000 grit graded sharpen, we get an edge that can be significantly enhanced with the 1,2,3 micron stropping paste that comes with the Tormek.

This is why its possible to "bring back" a chisel or plane iron edge like Mike and I have experienced just by stropping.  The proviso is that said edge cannot have blunted much or its not recoverable, presumably because too much folding has occurred for the small micron size to cut it.

[Rob]

Further...many of us, me included have reported mixed results when stropping directly after sharpening ie the recommended method for max sharpness. By mixed I mean the edge seemed less sharp after stropping than it was after sharpening at 1000 grit.

Whilst not a 100% certainty, it is now considered most likely that that result is caused by operator error ie bringing the blade up at too steep an angle and therefore folding the edge.

[mike40]

I can see that it would be tempting to raise the blade too high on the stropping wheel while free handing or maybe applying too much pressure when using the jig, through impatience and the desire to see that mirror shine quickly.

I had already read a lot of comments on this forum about the subject before I tried sharpening/stropping for the first time, so with those comments in mind, I tried to error on the safe side instead of pushing my luck, and I got a really good result. I am now wondering how it will go with my Swedish chrome vanadium chisels which are harder steel than the inexpensive chisel I have  already sharpened. The same applies to my plane irons which are 62 HRC compared to the Stanley plane iron which is probably around 59. I am expecting that I will have to use more time stropping them.

I like reading and learning about the technical aspects of sharpening, but my real concern is how my edges work in actual use and how long the edge lasts before the need for re-stropping or resharpening. Of course that is a rather subjective test, as one man's satisfaction could be another's agony. I can't think of any other quick way to test sharpness than the fingernail, pine end grain and paper tests, but they don't tell you how long the edge stays sharp.

[Herman Trivilino]

So, he is only saying, that:  If you sharpen to 0.5 microns, using any of the honing compounds that he tested results in a degradation of the edge.

Unless you're trying to add a "tooth" to the edge.

[Rob]

which for those who might think that counter intuitive to a sharp edge....is useful for certain applications, in particular kitchen knives that are destined to cut soft fruit and veg like tomatoes.  The "tooth" assists in cutting through the resistant skin

[mike40]

Hi guys. I'm not too concerned about the kitchen knives. Serrated knives cut the tomatoes pretty good anyway. My wife told me she doesn't want the carving knives super sharp. Of course that won't stop me from making at least one Tormek sharp whenever I will be doing the carving. I just finished doing my first good quality chisel. I'll tell you about my experience with that and a couple of other things with some photos after my camera battery is charged a little later today. I'm sure you will be waiting breathlessly for that post, ha, ha.

[Herman Trivilino]

How many degrees do you have Herman?

Just enough, Rob.  But not too many.   

[Rob]