March 2002 Newsletter

Stockton Astronomical Society

Valley Skies

Valley Skies - March 2002 Issue

The Telescope Nut
by Jeff Baldwin

Massive Polishing Party

Oh man! You should have seen the group of guys pushing the lap on the 40" mirror. Imagine four to seven guys pushing a 300lb concrete lap around on a large mirror, and others standing by to jump in when somebody gets exhausted.

At the end of the session, the mirror was surprisingly shiny. But, painfully, it was all for nothing. When Eric, Lloyd and I tested the mirror for astigmatism, it failed...miserably.

We still have tons of work to do on the mirror.

Steve, Seph, Eric, Paul and Lloyd grunting. The only thing missing was the drum beater.

Here's our theory:

The mirror was ground on a 55 gallon drum with a large 3-layer plywood tabletop. It was quite unstable, but got the job done, we thought! We only went to the concrete barrel after we had begun polishing, when the warp was apparently already in the glass.

When we were grinding with the 12 and 5 micron grits, the binding was miserable. That should have been a sign to me that there was a glitch. So, the plan now is to go back to 220 grit, drive out that nasty warp, return through the grits to 12 and 5 micron grits, and see how it feels.

Haji and Eric 'reflecting' on the results of the polishing session.

If I get through these two grits this next time without a problem, then I'll continue with polishing pads on the concrete tool. If it binds again, I'll take it back a few grits until it feels right.

The setback is disappointing, but I'm confident that things will work out. However, you should have heard the nasty words I used that night. If I were just planning to use this thing at radio frequencies I wouldn't have to be so particular!

Good friends are a good investment.
The Group...from left around the mirror: Lloyd Altamirano, Eric Reichenbach, Steve Scott, Haji Mukasa, Monte Schindler, Paul Neidhamer, Seph Walker, Trevor Atkinson, Kevin Hall and Jerry Hyatt.
(Hey, did you notice that most of the people in this photo have the same hairstyle as me? )

We made the mistake of telling jokes while we worked. That doesn't mix very well, especially since we were full of pizza. Tylenol stocks rose the next day.

The mirror became very smooth very quickly, which is nice, but we ought to have realized that something must be wrong - it's supposed to be a slower process than this. At least we know that when it is a surface of revolution it ought to polish quickly again.

Clear Skies...Jeff Baldwin
For more information on Telescope Making jump to the ATM page.