The Grinding Workbench

I set back to work on my telescope yesterday, November 18, 2001, after a hiatus of several months. I'm a software consultant, and things have been tough for everyone in the computer industry - hundreds of thousands of layoffs, many companies going bust. I have been working steadily, but unsure of my continued employment, so I was spending all of my spare time searching for new clients, even traveling out to the San Francisco Bay Area so I could interview on-site.

Happily, my client of the last few months agreed to give me steady work for the forseeable future so I could relax. That means I now have some spare time to put into telescope making.

Recently I found out about the Central Maine Astronomical Society from the ATM mailing list. I found out about it the most roundabout way - a class on telescope making was offerred in a local night school! I showed up to the class, only to find out it was canceled, but then asked after the teacher on the ATM list, and then someone told me he was in the CMAS, which meets the second tuesday of each month in Newcastle, a half-hour drive from my home in Owl's Head.

At the one meeting I've been to, I found out about their new observatory and last friday my wife and I went and looked through their 16 inch reflector. The observatory is in a field behind CMAS treasurer Colin Caissie's home. Colin showed me through his impressive optical workshop and showed me a lot of glass, from raw to aluminised, that he and the club owns. He also lent me several telescope making books.

Anyway, back to the workbench...

I built the workbench yesterday, it has a simple frame made of 2x4 boards and a 3/4" plywood top. It is 27" high, 32" deep, and 48" wide. I made it a little low so that when sitting, with the thickness of the plaster grinding tool, the mirror would be at a comfortable height. The front edge of the plywood top overhangs the front 2x4 by 6" so I have room to scoot my legs underneath. It is much bigger than necessary for my 8" but should be useful for grinding moderately large mirrors, maybe up to 16".

I planned to make two workbenches out of one plywood sheet and a half dozen 8' 2x4's, the other being a taller one for my wife to stand at. I had the plywood cut to size at the lumberyard. The cuts gave me a 1' wide strip that I used for a shelf down low in the back underneath the workbench.

With my previous telescopes I got pretty elaborate about my grinding bench. I've decided that this isn't really what you want, what you want is just something really sturdy you can sit at, or I suppose for a larger mirror something you can stand at. With my first couple mirrors I had a tall, narrow homemade table and could walk around the tool as I ground. With my 8" f/6, the third mirror I ground, I bought a lazy susan bearing and had the tool mounted on a disk that was mounted on the lazy susan.

I think what really works best for small mirrors is to just wet some paper towel and put the tool on it, then turn the tool periodically by hand. But it really helps to have a sturdy table so it doesn't rock around. The bench I made is pretty solid, constructed with wood glue and nails.

Unfortunately I didn't get the frame all that square as I nailed it together. I would square it as best I could then drive two nails into each joint. I think what would have worked better would have been to just put one nail in apiece, then stand it on the floor in its final position and give it a final squaring before nailing it off.

It rocked badly when I first built it so I cut 1/4" off two of the legs. It stands steady now but the top is shaped like a potato chip!

It has gotten too cold to grind in the garage and soon it will be freezing, so my wife suggested I grind in one of the spare bedrooms, the one my cat has taken up residence in. Eventually we'll put an oil heater in the garage.

My wife helped out by giving it two coats of green paint. When I grind, I'm going to cover it with plastic, and put plastic on the floor, and change plastic between grades of abrasive. I bought a 4'x100' roll of 4-mil polyethylene sheet at the hardware store today.