minimal workspace for grinding lenses

What is the minimal workspace one needs to grind telescope lenses? I have
some idea of the process as a result of reading Strong's book, Procedures
of Experimental Physics, a couple of decades ago. On the other hand, someone
contemplating grinding lenses in a small apartment has to find a way to do
it with a minimum of space. It occurred to me that instead of walking around
the work, one might be able to mount it on some kind of rotating platform.
That would probably do a lot to reduce the space requirements, but I'm
not sure what kind of rotating platform would be consistent with the
requirements of telescope lens making. Does anyone know?

Apart from that, there must be a lot of other improvements that can minimize
space requirements and other requirements such as a water supply. If one
runs a hose to a bucket, maybe one doesn't have to empty the bucket too
frequently and one can then work in a garage without plumbing. Is that
the case?

If the work can be set up in a bathtub, leaving enough room to stand next
to it, one has a water supply. I don't know what kind of work platform
(including the rotating base for the work) would fit in a bathtub and remain
steady. I also don't know if one needs to cover up the work when one takes
showers or if one needs to remove it, but that seems like one possible work
site in a small apartment, and one where it is easy to clean up the mess
caused by the work, and where one can still use the work area for its
normal functions.

Ignorantly,
Allan Adler


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Allan Adler asked:

What is the minimal workspace one needs to grind telescope lenses?

Allan,

I have extremely little knowledge or experience, so this reply
has a street value of about 2 cents, after inflation.

I worked on rough grinding a mirror both indoors and
outdoors for Astronomy Day and Spaceweek demonstrations,
where I stood behind the table working on the mirror, and
people came up to the other side of the table to watch.
That didn't work too bad. Though I still haven't finished
the mirror....

(The three most-frequently-asked questions:
#3: What makes it curve?
#2: What are you doing?
#1: Where is the restroom?)

I also tried putting the mirror on my kitchen floor while I
knelt on the living room carpet to grind it. (With a fairly
wide opening between the rooms.) That was some years ago and I
forget how well it worked. I think it was pretty clumsy, but
there was almost nothing to set up or take down. Wet newspaper
held the tool in place on the smooth floor.

Working in a bathtub could be hard. The lens and tool need
to be at a comfortable level. You could sit down if you make
some kind of chair to fit over the edge of the tub, so that
you can put your feet in the tub while you work! Two things
you CANNOT do are sit on the edge of the tub (all tub edges
I've experienced make awful seats) and bend over the edge of
the tub while you work (your back will not last).

Don't wash anything down the drain. I think the grit, and
maybe the glass particles, too, are so dense that they will
get stuck in the trap! Bad news!

As long as your work surface doesn't wobble or slide, you
should be fine. Something you can rotate and then lock down
would probably be good.

-- Jeff, in Minneapolis

Subtract 1 from my e-mail address above for my real address.
..

Greetings and Salutations.

On 05 Oct 2003 04:03:53 -0400, Allan Adler
wrote:


What is the minimal workspace one needs to grind telescope lenses? I have
some idea of the process as a result of reading Strong's book, Procedures
of Experimental Physics, a couple of decades ago. On the other hand, someone
contemplating grinding lenses in a small apartment has to find a way to do
it with a minimum of space. It occurred to me that instead of walking around
the work, one might be able to mount it on some kind of rotating platform.
That would probably do a lot to reduce the space requirements, but I'm
not sure what kind of rotating platform would be consistent with the
requirements of telescope lens making. Does anyone know?

Very possible. I did this some years ago and it worked fine.
I only did an 8" mirror, though. For anything larger, a more
elaborate workspace would be necessary. The good news is that
grinding lenses takes even less space than grinding a mirror.
I would strongly suggest you poke about the used book stores
and see if you can find a copy of "Amateur Telescope Making", volume
1, edited by Ingalls. It is still arguably the best reference for
this sort of thing, and had suggestions for a number of ways of going
about it.
Coincidentally, there is a VERY reasonably priced copy on Ebay
just at the moment:
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3555296234
and others are usually kicking about. There is another good book
by a french author, whose name escapes me right now that would be
helpful too.
Also, of course, a google search is a GOOD thing. There are
a lot of folks that have done this, and, posted web pages about it.


Apart from that, there must be a lot of other improvements that can minimize
space requirements and other requirements such as a water supply. If one
runs a hose to a bucket, maybe one doesn't have to empty the bucket too
frequently and one can then work in a garage without plumbing. Is that
the case?

Don't need that much water...more in a minute.

If the work can be set up in a bathtub, leaving enough room to stand next
to it, one has a water supply. I don't know what kind of work platform
(including the rotating base for the work) would fit in a bathtub and remain
steady. I also don't know if one needs to cover up the work when one takes
showers or if one needs to remove it, but that seems like one possible work
site in a small apartment, and one where it is easy to clean up the mess
caused by the work, and where one can still use the work area for its
normal functions.


Ignorantly,
Allan Adler


When I started on the journey of making my first mirror, I
faced much the same problems you have described. Here is my solution.
First off...while this is not heavy construction, there can
be a fair amount of "push" involved in moving the mirror. One wants
as stabile a base as possible for this. I had a desk in my room which
I bolted to the wall with a couple of "L" brackets and some lag
screws. A kitchen counter would work fine too.
I then built a small table out of heavy plywood and 2"x4"
stock that was tall enough to raise the mirror to a comfortable
working height when it was placed on the desk. As I recall this had
8" legs or so.I made the top of the table a square about 10" on a
side. The plywood was some 1" thick stuff I pulled off the scrap
pile. I cut three cleats about 1/2" thick, by 1 1/2" wide by 2"
long, and screwed them, spaced at 120 degree increments, around
the grinding tool (the tool was an 8" disk of heavy glass, same size
as the mirror). I set two of them permanently, and, cut a slotted
hole in the third cleat, so I could adjust it as necessary. My goal
was to have the ability to clamp the tool firmly, but, loose enough to
allow me to turn the tool. I put the two fixed cleats on the
"back" of the table, so, when I pushed on the tool/mirror, I was
pushing against the fixed blocks.
I acquired a basin (in my case, it was a small sink. However,
any water-tight container large enough to hold the table would do.)
Since the sink was metal, I could just set the grinding table inside
it and push it up against the back wall. I had planned on screwing
it to the basin, but, I found that by putting a chunk of 2x4 across
the back two legs, just below the top of the basin, it would
wedge firmly enough that I had no problems with it moving. I suspect
that if you are doing this on a kitchen counter, you would likely have
to rig up a frame to push against the wall and take the forces.
Finally, I clamped the basin to the desk, using a chunk of
rope. I made a large loop that went around the front legs of the desk,
and over the top of the basin but under the grinding table. It was
pulled tight with a turnstile arrangement. I had a situation where I
could set it up and leave it, though, so I did not have to worry
that much about taking it down and getting it out of the way.
After this preparation, I had a good, solid platform to work
on, and, shortly thereafter went to work, pushing the mirror back
and forth, grinding it into a sphere. My technique was to take
several strokes, then, rotate the mirror slightly (half an inch or so)
counterclockwise, and the tool roughly the same amount CLOCKWISE.
This ensured that I was always working across a different chord of the
tool, and helped keep the shape going spherical, and not
saddle-shaped.
As for water...I had a plug in the drain of the basin, and
during a typical session would collect perhaps half an inch of water
at most - a couple of cups all told. It was very easy, with a couple
of five gallon pails, to provide all the water I needed with no
plumbing.
When I finished a session, I would rinse everything off really
well, then, cover the entire workstation with a large sheet of plastic
to keep the dust off. I also started each session with rinsing the
mirror, tool and workstation down, so, had little trouble with stray
bits of junk causing scratches.
Hope this helps.
Regards
Dave Mundt

"Dave Mundt" wrote in message
.. .
I would strongly suggest you poke about the used book stores
and see if you can find a copy of "Amateur Telescope Making", volume
1, edited by Ingalls.

Also, "Standard Handbook for Telescope Making" which I think is much easier
for an inexperienced glass worker to master. Or even Jean Texereau's "How
to Make a Telescope" although its advice has a distinct European flavor.
Both of these, and the Ingall's book too, are pretty far out of date as
regards the names and sources of supplies, but they're all interesting to
read, they all give the basic techniques, and they're all available through
Amazon. My first and only telescope mirror, an 8-incher, was ground on a
board screwed into the top of a 55-gallon drum with holes laboriously
drilled through the thick steel top for draining the water and abrasive
residue (this was in the 1960s and my family didn't own an electric drill,
so imagine hand-drilling about a hundred holes through steel). It didn't
take up much space, it had its own built-in disposal for the waste products,
and when it was done I rolled it back into the woods from whence it came.
- Steve R
St Louis