Re: Homemade M2 friction folder/microbevels, microchips, and edge stability.

Hi Jimmy,

Sorry for my tardy reply, but have been away from the computer.

What are you looking for on the area away from the edge? The edge is
where all the cutting happens, so that's where I'd want to look.

Consider this: At 400X a 0.25mm length of the edge would appear as
100mm, clearly out of the field of view of the microscope. So what you
would end up looking at is an extremely small segment of the edge, not
representative of the whole, which is what you should be aiming to
examine.

In metallurgical microscopy, the rule of thumb is to start at low
magnifications to gain an appreciation of the whole and then increase
the magnification as needed to view particular features. For
sharpening, there is little to gain over 50x and often 20x suffices.
Read Verhoeven on this. http://www.bushcraftuk.com/downloads/pdf/knifeshexps.pdf


I would have thought that the advanced research used electron microscopes because they can
get higher resolution than optical microscopes.

No. The primary reason is that electron microscopes give far better
depth of focus and as well can provide magnification beyond that of
optical systems.


It seems to cut that way, but if a good edge is supposed to be <1um,
you'd think numerous 10um chips would bring the 'average' sharpness
down quite a bit.

If most of the edge was so damaged yes, but to ascertain that this is
indeed the case, we must first examine the edge at lower mags, say
20X-50X. A 10um chip at these magnifications would be visible because
it would reflect light. The surface of the chip probably won't be
discernible, but that is secondary in importance. More relevantly, a
low power examination could disclose the origins of the chips by the
evidence on the bevel in the vicinity and permit corrective action.


I seem to remember reading that most of the initial dulling is due to
deformation/microchipping, and if this is the case, it seems that the
stability of the very edge is the dominant consideration for retaining
very high sharpness.

Right on.

I have never had good luck sharpening with sandpaper or 1um diamond
lapping film (though I grabbed it out of the 'trash' pile after it had
been used to polish fiber optics- maybe the paper was messed up?), but
I guess I should try again, using 2000 grit SiC paper instead of the
~8micron lansky UF ceramic.

Just make sure to use edge trailing strokes and also ensure that the
burr from the previous stone or paper has been removed. Burs tend to
break off and damage the edge and this can lead to microchipping,
especially with edge leading strokes. Also, keep the pressure very
light. For the very finest edges, it is better not to raise a burr, or
only a very small one. This where a good low power microscope really
pays dividends.

I've been finishing with paper loaded with Dico brand stainless steel
buffing compound (dunno what is in it or the grit size, but it works
well), and I think I'll continue with it.

IME, when dealing with M2 and similar very hard steels, only silicon
carbide and harder abrasives, such as diamond, will abrade the
carbides along with the rest. Most metal polishes appear to contain
aluminium oxide which is significantly softer. Again a low powered
microscopic examination will reveal if the bevel is flat, or whether
some a constituens are standing in relief because they abrade more
slowly due to their higher hardness.


Why is stropping with diamond OK, but diamond plates are not? Would a
trailing motion on a diamond plate work, or is it a grit size
difference thing?

The action of a particular abrasive is determined by how the particles
are pushed against the work piece's surface. On a plate the diamond
particles are held firmly in a nickel matrix and their action tends to
be far more aggressive (read as rough) than if the same grit particles
were embedded in a soft carrier such as leather, with plenty of give.
Also some diamond particles break loose from the plate and sit atop
the other embedded particles giving raise to a very rough lapping
action. To a much lesser extent this also occurs with water stones and
why the high grade stones tend to be relatively soft. As well, with
some plates the nickel that holds the diamonds particles contributes
to the damage and IME EzyLap is a bad offender, though DMT is not far
behind, especially when new. For this reason it is always a good idea
to break in a new diamond platre before using it in earnest

In short, the same abrasive particle will yield vastly different
scratch patterns on different carriers. IME, and that of Verhoeven,
diamond plates give a far rougher finish than the equivalent grit
water stones. For this reason, it is better to confine the use of
diamond plates to rough bevelling and finish off on water stones or
abrasive papers. In this regard, the Lansky is a handicapped system
because it does not have decent fine stones, though this can be worked
around by the use of abrasive papers glued to a stone.

Regards
Craig

.

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