Dob Repaint pt1

The GSO 8" f6 Dobsonian gets a new coat of paint...

By Antony McEwan

I’m sure you appreciate the irony: Oxygen, the chemical element that is essential for us to live, gradually kills us. We depend on it, taking it inside ourselves in every lungful of air we breathe, and yet once inside us it oxidises and forms the destructive molecules known as free radicals, which contribute to cell breakdown and ageing. No surprise then that if Oxygen does this to the Human body, it can also destroy our telescopes.

I’m talking about rust. Rust that slowly, insidiously, develops and starts to break down the properties of metal, eating through paint, and forming reddish-brown blotches of brittle dead metal on the surface of your (or in this case, my) Dobsonian telescope’s tube. Nasty. Pic 1 (to left) shows the extent to which rust had developed in the three years I’d had it. All pictures shown to left will enlarge if clicked upon.

It was really quite bad, being concentrated mainly in two large areas around the middle area, but also spreading in smaller amounts into other parts of the tube. This was not a good situation, and I knew of only two ways to fix it. One was to strip everything off the telescope and put it back together on a new tube, and the other was to strip everything off the telescope, treat the rust, and paint the current tube. I chose the latter, as I fancied a change in colour. The silver grey was getting a little tired.

Having made the fateful decision, I immediately began to think about what colour to choose! I intended to use car spray paint, so that left me with a few thousand colour options available from Halfords! I considered Candy Apple Red, Apple Green, various shades of British Racing Green, Black, Sparkly Blue, and even one suggestion of Apricot Flash, but eventually saw exactly the colour I wanted on a car in my shop’s car park: metallic Peugeot Blaze Yellow.

Luckily, one of my friends, and a new member of the Highlands Astronomical Society, Angus Adcock, had plenty of experience with using spray paints, and was able to advise me on such arcane matters as primer, paint stripper and lacquer. Halfords was visited, and I obtained three cans of the paint, one of white primer, and one of lacquer. A medium size can of Nitromors paint stripper was also bought, and various pieces of sandpaper. I knew the other thing I’d need was time, so arranged to start the project when I had a week off work.

Disassembly

I’d never taken a Newtonian reflector completely apart before. The most I’d done was remove the mirror cell to clean the primary. To do this job I needed to remove absolutely everything from the tube; the trunnions, cell, spider, both mirrors, focuser, end rings, screws, the whole works! In actual fact, it was really quite straightforward removing all the pieces. Literally everything was screwed on, and it was simply a matter of undoing all the screws with a suitable screwdriver and storing all the parts carefully. Oh, and remembering where each bit came from, of course! I took some photos as I went along, to show the steps I took, and the basic simplicity of removing the parts. It only took a couple of hours to strip the telescope, until I had a completely bare tube with only paint and rust on it. All the other parts I stowed in a sturdy box and put out of harms way. Apart from the mirrors….

Knowing that I would have the telescope stripped down and inactive for a week or two gave me the opportunity (or excuse?) to send the mirrors away to be re-coated by Orion Optics in Crewe. They offer some very highly reflective coatings, known as Hi-Lux coatings, which increase the overall reflectivity of a telescope from the norm of about 75-80% up to about 94%. This means the images in the eyepiece will be brighter, so in effect the telescope will perform to a much higher level than before. Having already enjoyed some wonderful views through the GSO, I felt it deserved the pampering, so took the plunge. Sending the mirrors off to Orion Optics meant packing them up VERY carefully, and sending with extra insurance by courier. With that done, I could concentrate on the tube.

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