...And they're off

With the hoopla of Mars and all the other goings on in the Solar System, My mom started getting really interested in outer space. When I mentioned the telescope building workshop held every Friday for free at the Chabot Space and Science Center, she decided to treat me and herself to a new homemade telescope.

What follows is a work log of my very own 10" Newtonian telescope project.

January 23, 2004 (45 minutes. 45 minutes total.)

Opening night of my project. After some asking around, my mom and I each decided to build 10" newtonian telescopes on Dobsonian mounts. The setting was a loading dock at the back of the center where there were a ton of really helpful volunteers who patiently answered every question of ours. THere were people in various stages of grinding and lapping, starting with us 80-grit newbies in the far back corner, and becoming progressively more fine until we reached the three-micron-fine just-about-finished veterans in the front.

The tables are segregated in this way so that the fine tables aren't contaminated by coarse particles, potentially scratching the hell out of a finished mirror.

My telescope will have a focal ratio of 6 (F6) giving me a "longer eye" whereas my mom is going to build an F4.6 telescope, which should produce brighter viewing. This is all according to the people there. I hardly know what this all means, being not at all knowledgeable in any of this.

The upshot of this is that I will have a flatter mirror, while my mom will really have to work at carving out the center of hers.

We purchased the grinding tool and the glass lens blank, were given a cup of 80-grit scouring powder and were shown how to start grinding the blank down to its final shape. The process of grinding and lapping the blank into a decent mirror is expected to take 40 hours of work. The following pictures are taken after 45 minutes of effort.

Each picture is clickable for a larger image.

	Blank, meet grinder. Grinder, blank.
	Close up of my "mirror" after 45 minutes of grinding. Note how it's already starting to get concave in the center
	The grinder. Basically a slab of concrete with kitchen tiles embedded on it with some kind of resin. The resin coating has rubbed off along the edges and in the center, leaving a goopy ring that will eventually wear off as the mirror becomes more concave.

June 8, 2004 (four hours, 20 minutes. 5:05 total)

After two different grinding sessions and five more hours spend over the grindstone, here's some updated pics. I had to stop because I've run out of #80 grit, so it's time to go back to the workshop and pick up some more.

Grinding at this point is very satisfying in that, after about 30 minutes into the session, a grit-and-silicon paste forms up and fills in the spaces between the grinding stone tiles. This goop makes quite a seal. It's such a seal, in fact, that I can pick up the mirror by its edges while it sits on the stone and the stone will lift up with it. That tells me that the grinding stone is now fitting into the concave mirror and the whole surface is being used to grind.

	The mirror and grinding stone after five hours or so of work.
	The mirror. Notice that the ground section has reached the edge of the plate and now shows a uniform ground smoothness.
	Another shot.
	A shot with a metal bar resting on the mirror. It touches at the edges but gaps in the center. Yay! My mirror is getting concave!
	The grinding stone. All the goopy resin has been ground off and each little tile is getting smooth and a uniform convex shape is appearing over the surface.