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MikeMS

16 inch dobsonian build

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Hello.

I purchased a 16" F4.7 mirror in December, it was made in 1989 by Es Reid.

I built a dobsonian around it and apart from painted or varnishing it is almost done.

The focuser is for a SCT and at zenith the eyepiece is just okay for me at 5ft 11".

I got is out of one piece of 8X4 plywood and there are enough offcuts to finish a 10" dob that I have now finished too. The alloy tubing has plastic water pipe caps machined to fit with bolts in them. What else can I add? The mirror is very good and it is a joy to use.

The mirror cell sits on three bolts, with holes and small threaded rods in, but the mirror will lift out with the 6 triangle plates and connecting bars. This is the first dob I have built that you take off the top ring to move about. The mirror is too heavy to lay the scope down, but it does stay in play when you tip it down to view.

The bearings are kitchen worktop strips on the runners with telfon blocks and the base 4 small discs of a thick LP (vinyl record).

Mike.

post-3850-0-35440700-1394642534_thumb.jp

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Nice job MIke, a lot of thought went into that I'm sure. Is the spider something you built? Using LP record pieces for base bearings is something I hadn't heard of before, I learn something new every day here! Does the scope balance well?

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Thanks for the kind words.

I got the idea of a LP from somewhere on the web and the first time I used the entire album as the bearing. The discs are very small and as they run on untreated plywood it does need to be painted or varnished but it does work.

The balance is spot on, you just find the centre of gravity by lifting up the OTA and the side bearings pivot from that point.

The spider is a steel ruler cut in half.

This is my 4th strut tube dobsonian and it is just straight lines and curves, I have a router to cut both. And a little lathe to turn down the plastic caps to fit in the tubing. My friend did the welding.

As for using it, the optics are very good and M42 is bright and green!

I think this is as big as I will go, unless I can find a bigger mirror at F4 but then you are talking about a lot of money.

Kind regards,

Mike.

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That is nice and uncomplicated Mike.  I guess that with such a lightweight UTA, the 3 truss system copes well. do you have any more details on the plastic end cap truss connectors? I am intrigued.

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For the plastic inserts I take a plastic end cap used for water pipes, turn the outside down to just larger than the alloy pipe inside, put a bolt through the end and the nut on the side of the cap and tighten. Then I cut a short length of the pipe to put in the cap to fill up the space and then put it in the alloy tubing. It needs to be hit with a hammer and it takes off the excess plastic to make a very tight fit.

Picture here.

Mike.

post-3850-0-31750900-1394683317_thumb.jp

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Nice scope MIke, good  to see people coming up with their  own solutions  to telescope making problems, it's part of the fun of it. I have no doubt that the Es Reid mirror will perform very well.

John

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Hello Alan.

The waterpipe here is hard plastic and is grey. I do not know if that just happens to be the colour and texture though.

If you need some just say, in case it is difficult to get in the UK as it is normally copper.

Kind regards,

Mike.

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Well done mike. Scope's are very challenging to build and you've made a fine effort there with one that is finished and your happy with and rightfully proud of. I hope mine are as good and get as much praise

Damian

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