In article ,
Allan Adler wrote:
Donald Nichols wrote:
What I would do to examine the rack is to check it on an optical
comparator (after a through cleaning, of course).
I looked in my optics books and didn't find "optical comparator", so I
did a google search and found some information about it.
Your'e unlikely to find them in an optics book -- but a
well-equipped machine shop is more likely to have one.
Based on that,
I'm wondering whether an old microfilm reading machine I fished out of
a dumpster could be adapted for this purpose. It's housing is made of wood,
the optics are in metal and it is intended for strips of microfilm,
but I did manage to look at some crystals with it.
Those tend to have more magnification, and less depth of field
than an optical comparator for machine shop work. Also, the screen
tends to be a bit awkward to get to to add a transparent sheet to draw
on. The one I have apparently came with optional lenses for 10X, 20X,
and 40X, but I only have the 20X lens.
A proper one has a collimated illuminator, a stage on which the
object under test resides (with X and Y motion to move the viewpoint,
plus Z for the focus. Usually, there is a way to measure the X and Y
motion -- either with big micrometer heads to move the stage, or with
dial indicators to measure the motion.
However, there are minimal ones which are handheld, including a
set of reticles to measure various things including small threads, and
angles, an eyepiece, and a tube to join them. eBay auction #3855942073
has a set of reticles, but not the eyepiece and tube. I'm not sure, but
I think that the price there is a bit high.
Reliable tools has a nice looking one up for auction
#3856418973, but it's heavy (300 pounds), and is certain to go higher,
as there are over four days left.
There is another by Nikon which is still within reason, and it
suggests an alternative name "Profile Projector" for the equipment.
(Auction #3856039570).
I don't see any of the lightweight ones like mine -- it *looks*
heavy, but is mostly blown plastic shell and a wood base. The size is
necessary to get enough optical length for good magnification. Note
that it *will* take up a lot of benchtop space.
Try eBay searches for "optical comparator" (with the quote
marks) and one will show up sooner or later. A reasonable price is
somewhere in the $200-$300 price range. Unfortunately, this type is not
there at the moment. Note that the same comparator shows up in the MSC
catalog and in sales flyers for significantly more -- reasonable for a
business, but not for a hobbyist. The brand on mine is "Micro-Vu", and
the one on the MSC offering is Fowler, IIRC.
It's a piece of junk
but I've been reluctant to give up on it. The point is moot at the moment
since it is in storage where I can't get at it, but I expect that situation
to change. Even so, I'll need to acquire more practical knowledge about
optics than I have at the moment before tackling it. This would be a lot
cheaper than buying a comparator, I think, which would probably cost more
than a new scope. But I'm looking forward to trying out this comparator
idea for checking out the rack.
If you want to try to make one, the general design involves:
1) Illuminator on one side of the stage (or below it with a
transparent stage). (Plan on something like one of the Quartz
Halogen projector lamps in their own parabolic reflectors so you
have adequate brightness for good visibility in a well-lit shop.
Remember that the more the magnification, the less the
brightness remaining.
2) Moving stage for the device under test.
3) Lens to focus the image onto the screen.
4) Angled mirror in the back to bounce the image back and up
towards the screen.
5) Round ground glass screen with reference lines (cross hairs
plus angle lines and radius lines engraved in the glass, and
filled with black paint.
6) Ring surrounding the ground glass screen, with a full 360 degree
angle scale on it, and a vernier scale adjacent to it to allow
measuring to fifteen minutes or so.
7) Spring fingers (similar to those which hold slides on cheap
microscopes. These are used to hold the transparent films,
either for hand drawing to compare worn and unworn teeth, or
printed in a plotter from a computer, or photographically
printed, to compare new parts to their designed profile for
quality-control inspection.
Good Luck,
DoN.
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