Eight Inch Dobsonian Scope Rebuild

By Warren Bracewell

Dan Carver, who just joined the BVAC, contacted Randy Light and asked if the club would like to have and old 8" Meade Dobsonian scope that he had. Randy contacted me and I asked Dan to bring it over.

The tube of the scope was a Sonotube. It had gotten wet and the mirror was fogged. I took the scope apart, cleaned the interior and exterior, and set the tube in the sunshine to dry slowly.

I started cleaning the mirror and the secondary mirror and they were in surprisingly good condition. I found that the spider vane was loose and missing two of the acorn nuts. I replaced the nuts and tightened.

I found that the focuser was gummed up and sticking. I took the focuser apart and cleaned all of the dirty grease from the rack and pinion gears. I re-greased the gears and reassembled and adjusted the tension.

The focuser worked smoothly after that.

The scope had a small 6 X 30mm finder scope attached that you couldn't see through. I removed the finder scope and took it apart and cleaned the lens. Once it was cleaned, I noticed that the crosshairs were messed up. I straightened them with a toothpick and the finder scope appeared in pretty good shape then.

The original base of the scope, I was told, had fallen apart, and one was made of plywood. That base had gotten wet as well and was warped and would not turn. I decided to go ahead and rebuild the base. I purchased some melamine particleboard, HDPE plastic, and hardware and using the other 8" Dobsonian base as a pattern, rebuilt the base.

The scope came with three 1.25" lens. It had a Meade MA25mm, a Meade MA12mm, and a Plossl 4mm. I cleaned the optics on them as well.

After everything was back together, I collimated the scope and took it out for a try. I was pleasantly pleased with the results. I checked out the moon and Jupiter and Saturn and was able to discern quite a bit of detail. I turned it on M2 and M15 and could make out individual stars. I looked and M57 and could definitely make out the ring.

I think that this scope will make a great addition to our collection of club scopes. The only upgrades that I would suggest is to add a better finder scope and/or a Telrad.

Eight Inch Dobsonian Scope Rebuild

Rebuilding the Dobsonian