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 snipped-for-privacy@zurich.ai.mit.edu
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. .
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:
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others are usually kicking about. There is another good bookby a french author, whose name escapes me right now that would behelpful too. Also, of course, a google search is a GOOD thing. There area lot of folks that have done this, and, posted web pages about it.
Don't need that much water...more in a minute.
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
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.
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