Instructables

Smaller Dobsonian telescope

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I was been missing making a telescope, but didn't need another one. So I persuaded a colleague to make one with me. The optics were cheap--a 6" F/5 mirror (with a 1.5" secondary) from a Cloudy Nights seller for about $60. In classic style, this was going to be mounted in a Sonotube, with most of the rest made of 1/2" Baltic Birch plywood.
 
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Step 1: Altitude bearings

Picture of Altitude bearings
I used a router to cut altitude bearings from 3/4" red oak. They are slightly more than semicircles. It's traditional for altitude bearings to be circular, but using semicircles (or slightly more), the radius could be made larger for semicircular bearings without wasting money on a wider board, thereby making for greater stability. Moreover, it's easier to cut less than full circles on my fixed-base router. And I cut lightening holes with a hole saw.

Step 2: Mirror focal length

I measured the focal length of the mirror at around 29". The time before that I measured the focal length I projected the moon onto a piece of wax paper, and then measured the distance. That wouldn't work this time, as we didn't have a moon in the evening sky. So instead I put a red LED light some distance (d1) away from the mirror surface, focused it on a piece of wax paper, measured the distance of the wax paper from mirror surface (d2) and used the formula 1/d1+1/d2=1/f, where f is the focal length. I did this twice and averaged.

The mirror did have a chip on the back side, and I was worried that this may have set up stresses and distorted things, so I tested it as described in this post , and it was fine. Hurrah. 
This is amazing. I'd never heard of a Dobsonian before, but you've inspired me to do some more research from home.