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Astralstroll

New Dob Build - Top Half

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For the present, I am going without an offset on the secondary. Can always rectify this later if needed. It's taking me enough time to get around to gluing it never mind the complexities of an offset.

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Calvin, I'm finding black is best for hiding my less than perfect craftsmanship. If I get better with future builds, and also choose some better ply, I might go for a different colour. For the moment, I'm sticking with black.

Dave.

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I have finally successfully (?) silicones the secondary mirror to the support. I had previously treated the plywood surface with a couple of coats of epoxy. After a quick sanding and clean up, the mirror was attached with three blobs of clear silicone, 120 degrees apart. The mirror was spaced from the plywood support to allow removal if necessary with a hacksaw or similar tool.

Now the next question, the upper surface of the mirror and mirror edges wil need to be blackened. Do I take the safe, but less aesthetic approach of painting, or the neater, but more risky option of spraying? When I finally get this bit sorted I will add a before and after pic.

Dave.

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I wouldn't go anywhere near an optical surface with a spray. Just paint the edges or use a felt tip pen. The edges are normally ground and non-reflective and it is best to try to maintain that non-reflective character as much as possible.

Nigel

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Id agree with nigel, buy a sharpie pen and dont go anywhere near with spray.

The problem with soray is the aerosol can get attracted by electrostatic charges so can end up in places where you dont expect, and its not just the paint as the propellant gasses could be attracted too.

Cheers

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I painted the last one Dave and will on the next one which will be pretty soon as I had the trusses, UTA and LOA fixed together the other day.

Today I'm on with a jig to drill the bush holes on the alt bearings. Then its drilling the LOA to mount the alt bearings.

All looks pretty good and nearly there

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Nigel, Astro,

That was my worry with spraying. I think some very diligent work with a small brush or a pen are in order. Many thanks for the advice and warnings.

Dave.

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Looking really great Dave, can I ask what paint did you use for the black finish on the wooden cage and did you spray or brush?

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Simon,

I used Wilko Matt Black interior and exteriors quick drying paint for wood and metal. It goes on well, but you have to watch out for the occasional drip.

Dave.

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Simon,

I used Wilko Matt Black interior and exteriors quick drying paint for wood and metal. It goes on well, but you have to watch out for the occasional drip.

Dave.

I used the wilko blackboard Matt black interior and exterior paint for the inside of the box and UTA seem's to brush on well.Three coats of Ronseal clear satin on the outside.
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Simon,

I used Wilko Matt Black interior and exteriors quick drying paint for wood and metal. It goes on well, but you have to watch out for the occasional drip.

Dave.

I used the wilko blackboard Matt black interior and exterior paint for the inside of the box and UTA seem's to brush on well.Three coats of Ronseal clear satin on the outside.

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Thanks Dave/Mapstar, the finish looks really good. 

I've been scratching my head how to finish mine, I want it black, but cannot decide whether to go stain or paint.

Think I might try the Wilko paint on an off cut and see how it looks, cheers!

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Simon,

I hope the painting is coming along nicely. Black still seems to be the colour of choice with most scopes. Not the most exciting of colours, but it's very practical.

Dave.

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Well, I have finally "finished" the secondary cage. Mirror silicones and the safety line attached. Telrad base and finder scope shoe attached. I still need to cut the safety line to length, but most likely do that as and when I get the final collimating screws sorted. Next job is to get the thread up for the now completed lower half, and then marry the two together by cutting the poles to length. Another nerve shredding job no doubt!

Dave.

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Many thanks Alan. Seems a long time ago when I startd. Last August Bank Holiday to be exact. Definitely on the home straight now.

Dave.

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It's looking really well finished did you go for painting the secondary black?

Might sound like a silly question but what make of silicone did you use to glue the secondary as I've just used some Dow Corning glazing seal and it was rubbish peeled straight off! Not a happy bunny! :-(

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Hi dave, it looks really good in its black paint.

Onenthing ive noticed, and im not sure if I dare say, but it looks as if the secondary mirror is the wrong way round ie take it off the stalk, rotate it 180 degrees and stick back on. As far as I know the edge of the secondary that you have painted black should face the sides of the tube, not down the tube as you have it ..... maybe someone else could add their thoughts though?

Looks really nice though,

Cheers

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Astronymonkey,

Thats what I get for saying the top half was finished! Now I look at the image I posted, it definitely looks upside down. Guess I will be learning the art of secondary removal this evening. Hopefully I will get it sorted later.

Dave.

Edited by Astralstroll

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Well spotted Astromonkey. You have keen eyes Sir.

Only a small glitch Dave. Good practice for the next build :grin:

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Alan,

I always wanted to learn how to remove the secondary, just not this soon. Thankfully, I did put some adequate spacing in between the mirror and the support. Will be setting to work this evening.

Dave.

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Looking good Dave, bit of a distance between your Telrad and focuser is that going to work okay?

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Steve,

at the moment I think it will. If it proves to be an issue later on, I will relocate the board with the Telrad base closer to the focusser. Something is telling me that once built, there will be a period of slight modifications. Still, thats all part of the joy of self builds. At the moment, I need to stop thinking ahead to future builds, and get this one finished.

I currently have two more builds in my head that need to be temporarily forgotten about.

Dave.

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You and me both Dave ;)

Next build is always in the back of ones mind  :grin:

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