Your reply is a great one, and a large serving of stuff to digest, DoN.
Thanks for including the detailed info concerning the glass fibers. I had no
previous knowlege of the glass strands other than some of the early ones
were made in tall tower-type structures at one point IIRC.
I hadn't realized the necessity to keep the individual fibers in correct
order/orientation to reproduce a proper image until you mentioned it. Yeah..
I could see where that would matter, heh.
The ITI brand fiberscope I mentioned was apparently a fairly good one, when
it was new. It's one of the flexible ones (3mm dia.) that can be articulated
near the tip by two fine stranded wire cables tied to a knob on the
hand/eyepiece/body.
Clever little gizmo that works similarly to the earlier mechanical remote
control automotive outside side/rear-view mirrors (but only two opposed
directions, not four).
I took Mark's mention of bending a thin glass fiber to suggest it would be
possible with thin HSS, as you mentioned.
I was originally thinking in terms of the traditional process of producing
bandsaw blades, which would require the cutting edge to be .025" or .035"
thick (as those are common thicknesses of bandsaw blades).
From there, the strip of hard material that's typically the hardened tooth
material area on bandsaw blades, is wider than the thickness by many times
(looks like about 5 times wider or more).
The wheels on my 4x6 bandsaw are maybe 10" diameter, a port-a-band maybe
smaller, but larger wheels on big saws naturally, and the possibility of
running a brittle material around wheels with the numerous high forces
mentioned earlier, seemed highly unlikely to me.
Previous to Mark's example, Robin had referred to a somewhat new technology
developed by Starrett, where two thinner ribbons/foils of HSS are fused
to/with the region near the edge of the supporting band material, resulting
in a "steel on HSS sandwich" at one edge of the band.
Then, when the tooth profiles are ground or milled into the edge of this
region, it leaves less than the full width of the HSS ribbons/foils to
bend/flex/twist etc. (or possibly even interrupted HSS-clad teeth, the image
wasn't very detailed and the description not very specific).
Ed had mentioned Sandvik solid HSS power hacksaw blades being thick but
somewhat bendy.
As per your suggestion of 1/8" cobalt making a wrap around maybe a 10'
wheel..
An extremely long 1/8" thick solid HSS saw blade would've been handy for the
cruise ship retrofitters that were assigned the task of adding a section in
the center of a cruise ship, so they proceeded to cut the ship in half, and
added the section.
I don't know that the story was true, but there was an online story about
it, maybe a couple of years ago.
--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html
"DoN. Nichols" wrote in message
...
The fibers are typically two different glasses, selected for
different index of refraction, one solid as the center, and the other
hollow around the first. They are heated and the ends drawn apart, and
the outer sheath collapses onto the inner core and they fuse together.
I have seen rigid fiber optic devices which have been made by
drawing down the center of a bundle, then cutting it in the middle,
grinding polishing it. The result is a bundle which will enlarge or
shrink an image. You can get these from Edmund Scientific or Edmund
Optics (I forget which sells that) as demonstration pieces.
You can also get ones where the fibers have been fused together
and then twisted while still hot enough for the glass to bend, so the
image is twisted 180 degrees.
I've also seen fiber optic bundles fused together in a
hex, then the center drawn out to make a smaller hex bundle, gathered
with more hex bundles to farm a larger one, then drawn again through
about three cycles -- then cut into thin slices and the inner core is
removed by chemical etching leaving a honeycomb prior to coating (vacuum
evaporation of metal) to form a channel for electrons as part of an
image intensifier tube. This was called a microchannel, and was used to
intensify the tiny signals which were common in serious astronomy. The
electrons bouncing along the tubes from side to side, and accelerated by
a voltage difference between the ends of the tubes, keep kicking out
multiple additional electrons every time they hit, thus increasing the
signal strength.
Before microchannels -- larger intensifier tubes were made with
rigid fiber optic bundles ground to a curve to match the electrostatic
focusing in the tube, and ground to flat on the end -- joined to two
other similar intensifier tubes by a silicone grease to couple the fiber
images together.
The limited information that I've discovered about mating lenses in
optical
equipment involves Canadian balsam (?) or special grades of epoxies.
This is normally for joining the surfaces (usually curved) of
different glasses to build a lens with just the needed index of
refraction. You'll find a lot of these joints in the more complex
camera lenses (faster and zoom lenses), and even the early Zeiss Tessar
design had four elements -- the rear two cemented together, then a space
for the iris diaphragm and shutter, and then two more elements which had
an air gap between them -- and for folding cameras typically had the
spacing between these two lens elements adjustable for focusing.
I haven't seen the interface at the eyepiece end yet, and I'm curious
about
how that's accomplished.
Well ... typically the bundle for the image scopes is made by
laying out fibers one at a time into a precise pattern, then fusing the
ends (leaving the majority of the length loose for flexibility) and
polishing the ends. The objective lens focuses the image on the flat
polished surface at one end, and the eyepiece picks it up from the other
end.
Aside from the occasional broken fibers (which increase with
use), there are also occasionally misplaced fibers which move a dot from
one place to another.
If *I* were to try to make an optimum quality image fiber
bundle, what I would try to do is to lay the fibers in a loop and
optically weld the ends together. (I've seen the device which does this
with fiber optic lines used for telephone and network here in this
neighborhood, and it is a neat device.) Anyway -- the welds would be
scattered around the bundle, and the clamped group of fibers would be
fused together (again two glass types -- the center for the optical
signal, and the outer to protect the inner fiber and to fuse to adjacent
ones). Once about two inches or so of fiber is fused into a rigid
block, I would then diamond saw through the block and polish both ends
to optically flat. This way, the fibers could not shift where the images
are formed, and it does not really matter how much they shift in
between, as long as they don't get broken. That's what the sheath is to
prevent.
------------------------------------------------------------
But I *think* that the original mention of how small a radius
bend you can put in a glass fiber was to suggest that thin HSS (which
you had said was as brittle as glass) could be bent to an equally tight
radius if it was no thicker than the glass fiber's diameter.
IIRC -- when someone in this thread mentioned solid HSS bandsaw
blades, he did say that they were thinner than the usual carbon steel
blades.
And from bending which I have observed in a HSS (actually cobalt
steel) parting blade with a maximum thickness of 1/8", I would say that
that can be bent into a circle of about ten feet diameter or so. And
that is a *lot* thicker than any bandsaw blade which I have ever used.
Enjoy,
DoN.
--
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