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How large for a first attempt at building?
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mvsopen
Joined: 25 Sep 2006
Posts: 5
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 Posted: Mon Sep 25, 2006 9:45 pm Post subject: How large for a first attempt at building? |
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I've decided that I want to build a Dob, and I've just ordered the various books and construction manuals. While I'm waiting for those to arrive, one question comes to mind: What is a good size for my first attempt at Dob building? I want to take my time and do things right, and I do have limited access to a decent workshop. I'm thinking about cutting, sanding and staining all the various wooden parts before I even order any of the optics. That way, if I don't like the job I just did, my only expense would be the cost of the wood. I'd love to build an "Obsession" quality Dob, but are such things even possible?
Suggestiions, please?
-Rich in California
(Other side of the pond) |
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Tony Legge
Joined: 13 Oct 2006
Posts: 8
Location: Cambridge, England
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| Posted: Sat Oct 28, 2006 3:08 pm Post subject: |
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| Rich, Size of telescope - I think that depends on where you will do your observations, and how good your lumbar vertebrae are. Do you have to move your telescope? My 10" Dobsonian weighs 20 kg, base plus OTA. My garden is OK for observations, so I don't have to carry far. That is Ok for me, but I wouldn't want to move anything much heavier than this if it had to go very far! Most peole will say 'as large as you can afford, and as big as you can carry.' So work out first what your scope will weigh as this may well dictate the size you go for. Best, Tony |
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justin138
Joined: 28 Oct 2006
Posts: 3
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| Posted: Sat Oct 28, 2006 7:57 pm Post subject: |
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I would agree with Tony, a major consideration is portability. Do you intend tranporting the scope in a car? If so, in my opinion, 10" is about the maximum you'd want to go to as any bigger and you start getting into the heavy side of things not to mention needing a van/large car to lug it about!.
Another consideration is for a scope with a mirror of 8" or less, the mirror cell is a lot simpler to construct as at the 10" scale, you start needing elaborate methods of mounting the mirror which can be a bit of a pain to make.
The mirror in my 7" home made dob is fixed to a round piece of MDF with electricians insulating tape and this works a treat! (believe it or not!)
Any more questions, fire away!
Regards
Justin
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10" Revelation dob
7" home brewed dob |
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mvsopen
Joined: 25 Sep 2006
Posts: 5
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| Posted: Tue Oct 31, 2006 12:30 am Post subject: |
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Thanks, guys! Another question: What about the bearings? Should I cut two half-circles from wood, or purchase a set of pre-made bearings (Which could be rather expensive). Everything seems to depend on the way the scope moves, so to me the bearings really are one of the most critical bits.
-Rich |
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justin138
Joined: 28 Oct 2006
Posts: 3
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| Posted: Sat Nov 04, 2006 7:04 pm Post subject: |
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| mvsopen wrote: |
Thanks, guys! Another question: What about the bearings? Should I cut two half-circles from wood, or purchase a set of pre-made bearings (Which could be rather expensive). Everything seems to depend on the way the scope moves, so to me the bearings really are one of the most critical bits.
-Rich |
For my bearings, I used drainage pipe plugs like these:
http://www.screwfix.com/app/sfd/cat/pro.jsp?id=18082&ts=66838
Mine are 110mm in diameter and they work a treat! Cutting half circles from wood is a good option if you are reasonably good at woodwork as they obviously need to be perfectly circular.
I'm a good woodworker but couldn't be bothered 
Here's a pic of my dob mount:
Hope this helps
Justin
_________________
10" Revelation dob
7" home brewed dob |
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gronk
Joined: 21 Sep 2006
Posts: 3
Location: Sydney, Australia
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| Posted: Sun Nov 05, 2006 9:36 pm Post subject: |
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I made a 25 cm (10 inch) Dob about ten years ago, and it still blows my mind. Yes, I get jealous when I look through Adam's 20-inch. Or Mike's 25-inch. But I still love mine, and portability is a bit part of it.
I am no woodworker or optician, so I found it crucial to hook up with people who actually knew what they were doing.
The big three suggestions I can offer are:
1. As everybody suggested, keep practical considerations such as portability in mind;
2. Get busy lookin for a club with members who are involved in telescope making, or contact an observatory to see if they have any contacts. You might get really lucky like I did, and find a course on how to do it!
3. GO FOR IT! |
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