Table of contents for ATM
- Playing Galileo on a Friday night
- Second week of amateur telescope making
- Third week of amateur telescope making
- Fourth week of amateur telescope making
- Finishing up the polishing of my telescope mirror
- Really wishing my telescope was finished right about now
- The zen of telescope making
- A triumphant telescope-making turnabout
- Slow and steady wins the telescope-making race
- And the mirror figuring goes ever onwards
- Week ∞ of amateur telescope making
- Mirror-making breakthrough!
- Progress on my telescope’s mount
I’ve made a lot of progress on my telescope since the second week. Just as a recap, I’m aiming to make an 8″ f/6 Dobsonian telescope, by hand. I’m still working on the 8″ diameter disk of Pyrex glass that is going to be my primary mirror. The last step is making it reflective by coating it with a layer of aluminum. I was at the workshop on Friday night for 3.5 hours. I finally saw some repeat people who had been there previously (besides the Guy running the place).
My night was fairly boring. I worked with 400, then 500, then 700 grit abrasives (the number is how many particles it takes to make one inch across). The particles are small enough now that it’s really important to make sure that they are always kept wet, so the dust they give off when ground up isn’t inhaled. There’s a famous astronomer who died of a really bad lung disease after making too many scopes and inhaling too much silica dust. His name escapes me at the moment.
The exciting part of the night came when a man who drove down from New York had his mirror aluminized. The amateur telescope workshop up there doesn’t have a vacuum chamber. He disappeared to the kitchen of the Community Center for an hour, thoroughly washing and re-washing his glass, making sure to get rid of every last bit of contamination. Then they started up the vacuum chamber.
The vacuum chamber is an old Navy relic that was originally used for God knows what. When it was too old for their purposes they donated it to American University, and then when it was then too old for their purposes, they donated it to the National Capital Astronomers, where it ended up in the amateur telescope making workshop. It’s not in bad shape though. It’s typical of military hardware: rugged as all hell, made from steel instead of wimpy plastic, and it does its job for its intended lifespan and then decades more.
It’s fascinating to watch the vacuum chamber in action. First, the mirror is loaded, upside-down, in a harness at the top of the vacuum chamber. Then an aluminum slug is inserted into a tungsten coiled filament at the bottom of the vacuum chamber and the dome of glass is lowered. It takes awhile for the vacuum pump to suck all of the atmosphere out of the chamber. Meanwhile, a diffusion pump is running through cold water coming from the sink, used as a coolant. Finally, the requisite level of vacuum is released, and a current is applied. Read the rest of this entry »
Read the rest of this entry »