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

Hi Jimmy,



Ah, more room in *that* dimension. Yes, your sample size is smaller,
but you should expect the edge that you see to be an "epsilon typical
edge", and after sliding the edge along and/or examining multiple
spots, you can get quite a bit more information.

With a jig setup like the lansky, I don't expect any large scale
variance in edge quality- I expect it to be homogeneous in its
quality.

If you were confined to a high power microscope and had no
alternative, I imagine that you could work backwards like that and
arrive at some idea what the whole edge looked like, but it is
convoluted and not the preferred way to go about it.


The "magnification" spec never made sense to me. If I display the
image in a tiny TV the magnification is lower than if I display it on
a large flat screen TV. It's the resolution that really limits you.

You are right - With microscope systems you can get what is sometimes
called "empty magnification". That is magnification without increased
resolution, much like blowing up a photograph and not seeing any
detail better. This kind of magnification is useless.

Optical metallurgical microscopes struggle at 2000x requiring oil
immersion lenses and have almost no depth of focus - In contrast SEMs
are capable of far greater magnification with correspondingly useful
resolution coupled to extremely good depth of focus, as evidenced in
Verhoeven's paper, which makes for interesting reading with some
excellent shots of edges at very high mags.



The light setup I had didn't allow me to see edge damage by
reflection, just by zooming in and seeing that there was a chunk
missing. If you get light coming from the right angle, I can see lower
magnifications being more useful- I had not thought of that.

What sort of microscope is it - Inverted stage metallurgical or
biological?

It did indeed look like the surface was ~10% covered in tiny chips.

Must have looked like a saw!


This seems to suggest increasingly tiny and increasingly steep
microbevels.

For MBs to work well they need to become progressively more obtuse as
they approach the edge. Otherwise a concave (hollow) edge) is the
result, which is generally undesirable.


If you expect cutting ability to be roughly inversely proportional to
sin(angle)*thickness, it seems that the tiny microbevels would not
hinder cutting ability even at obtuse angles, since thickness is so
small, but they could greatly improve the stability of the very edge.

On an all purpose knife that is the case. For razors cutting through
single strands of hair, not such obtuseness can be tolerated because
all the cutting action takes place at the thickness of a strand of
hair.


Why don't you hear more about this type of edge?

Many expert sharpeners tend to convex the last 0.5mm or so towards the
very edge in effect creating a progressively increasing bevel angle.
This is best achieved by way of stropping on mouse pads with very fine
abrasive papers or on leather charged with fairly coarse abrasives of
#800 and up. The correct use of a MB is the mark of an expert
sharpener.



I can use the lansky fine stone to get it tree topping sharp (and it
gets even sharper with the UF),

That's great, but how do you know that you are not cutting with a
"fin", an extremely small and tough burr? Such fins are very common
and very difficult to detect without a low power microscope. They are
very sharp but dull (roll) quickly if the blade cuts into something
substantial.


but when I take 1200grit SiC sanpaper
wrapped around the stone (slight bulging) and use very light edge
trailing strokes, I lose that sharpness. Perhaps gluing it to a stone
such that the surface is flat and rigid would help?

First you need to flatten a Lansky ceramic stone on a diamond plate,
as I haven't seen one yet that is flat. Then using double sided
adhesive tape you fasten the abrasive paper. After the Lansky #600 oil
stone the progression with papers ought to be 800P, 1000P, 1500P,
2000P, 2500P and maybe 3000P. Then strop. Alternatively, if you are
good at freehanding on mouse pads, convex the edge, but if going down
this route, use the 17 (26 degree included) as the microbevel will
thicken towards the very edge by something like 10 extra degrees
included, maybe more if using a heavy hand. The final angle has to be
estimated using a low power microscope. There are also other ways to
go about this.

I like the Lansky for small blades, but prefer the Edge Pro because it
offers a better selection of stones, a more precise action and one can
go to a much lower angle for the main bevel.

Cheers
Craig
.

Relevant Pages

  • Re: Apparent Distance
    ... >> gives a maximum magnification of 180x. ... >> can use magnifications in excess of x180 for the Moon for example. ... angle, but the tangent of half the angle. ... try this with a 5mm eyepiece. ...
    (sci.astro.amateur)
  • Re: Nikon D40 with 300mm lens AND teleconverter (Nikkor AF-S Teleconverter TC-20E II)
    ... It seems the accepted standard for a 'normal' focal length might be a bit on the long side, so if reinventing a sensible terminology from scratch it might make more sense to talk about the width of the sensor rather than the diagonal, which for 35mm would be a 36mm lens, for APS it would be a 24mm lens. ... telescope magnification factor back in the old days when people often ... I don't even think I could figure out the angle of view given a focal length, sensor size & a calculator, let alone do it in my head. ...
    (rec.photo.digital.slr-systems)
  • Apparent Distance
    ... The definition of a telescope's magnification M is standard. ... object that subtends a *finite* angle to the naked eye (so we are not ... where b is the angle the object subtends to when seen through the ... OB is the object's actual distance, the "apparent distance" will be OB', so ...
    (sci.astro.amateur)
  • Re: Focal length and angle of view.
    ... the angle of view assumes a 36x24 mm image area. ... It's just that a macro lens is designed to achieve focus at a reproduction ratio of at least 1:2 and preferably to 1:1. ... The zoom magnification has little do do with it. ...
    (rec.photo.digital.slr-systems)
Loading