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DIY DOB (mount) for 8"-10"?


BiG JiLM

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Hi- Ive been trawling through here hoping to see a diy dobsonian mount build (maybe for a 10" or 8" SW150/ 200 say, along these lines). In diy terms they seem a relatively simple thing to make. Can anyone point me to a thread if Ive missed it?

As Im a newcomer, but already setting sites on upgrading as I know Ive found a stalwart new hobby (should've done 15yrs ago!), can you tell me.. can I buy say a std SW 150 'just the OTA w'out EQ or dob braces' (ie just a bare tube with optics) and assuming the pivot sections on the OTA for a dobsonian are relatively simple, is it poss to buy a 'dob brace' to attatch around its midriff? ie for the two pivot points either side of OTA that attach to the dob mount.

If this is possible maybe therefore then build a dob base. I ask as it seems the very best bang-for-buck plan on paper, my funds are tight- but my DIY skills pretty good. Sorry if terms are not correct such as 'dob brace' but I can only describe as best what I mean w'out a heap more knowledge.

cheers JiLm

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Hi chaps- thanks for the replies, Moonshane your bigboy thread is a bigboy itself all of 18pages! but very interesting, I shall peruse when Im more atuned to the very basics, such as your 6" build -very much the idea I had a rough formulation of- and burucen's link too.

I am still slightly confused on the principle of the side bearings (the base rotator plates are straightfwd to see) in Brucen's link, and perhaps these then the std model for smaller dobs. Bearings is a term I can only ascociate with balls, in grease, and smooth metal sections moving against each other etc etc. But these simple side 'bearings' are what two lamnate faced wood pieces directly rubbing against each other? surely there must be more to it than that- I just ant see how that would work due to friction and jerkyness etc.

Thanks JiLm

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  • 2 years later...

Apologies for grave-digging.

Faced with making a Dobsonian mount for my 8" Newtonian, is this thread the best place to start? It's from 2012 - have there been other useful threads since then?

Richard

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BUMP

My internet research leads me to believe I either

  1. Spend £40 on the Kreige and Berry book or
  2. design my own Dobsonian mount from scratch

Right?

HELP!

Richard

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That does look like solution. I'll have a careful read through that thread.

There are some key dimensions I'm not clear about - eyepiece height for instance

Richard

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BUMP

My internet research leads me to believe I either

  1. Spend £40 on the Kreige and Berry book or
  2. design my own Dobsonian mount from scratch

Right?

HELP!

Richard

Sort of like BigSumorian said there are plenty of examples online that you can copy.  James' build description here, for example http://www.tanstaafl.co.uk/2012/08/my-10-dobsonian-build/

shows the same design base as the K&B book describe.  The difference with his build was with the bearings directly attached to the tube body.

So I'd say, option 3: pick a design you like make changes so it works with your telescope body and ask questions here.

I made my base from the K&B book appendix and it came out like this:

20150524 201628

Making a dob base like that, all  dimensions start from the OTA (telescope tube).  The diameter of the bearings (and the bottom of the base) should be around 1.8 times that of the mirror.  The ota fits inside the 'cradle' box with 1/8" inside clearance and is wedged in with cardboard (to allow you to re-balance it later if you add a new heavy accessory).  You work out the height the side of the base needs to be from the balancing point of the OTA - which is easy to do once you've made the cradle and attached the bearings, then add a bit of height for good measure.  For friction on the side bearings I used 3mm ptfe sheet pads and attached textured laminate to the side bearings.  My azimuth bearing is a lazy susan bearing with some milk carton lids inserted between the two base discs to slow the movement down, some people use a LP vinyl record instead of the lazy susan bearing.  
Also, use plywood (I used inexpensive exterior plywood from BnQ), a mix of 18mm and 12mm sheet (18mm is probably best).  Take your time and make sure cuts are square and sides are equal length (and everything glues/screws up square too - plenty of clamps are handy).  A hand held power router (for the circles and arcs) and a circular saw help here (though a router will cut decent straight lines with a guide).  

However, depending on what you already have the absolute cheapest option (if that's important to you) might be to sell your current scope and buy one with a dob base - not the fun option though but you might want to price up the costs before you start.  £50 for 'cheap' plywood, £10 paint, £20 for a lazy susan bearing (LP would be cheaper), £3 for ptfe, £3 for laminate edging etc ..  not counting the corner clamps, picture frame strap clamp or the power tools and hand tools (which I bought mainly for this project) mine cost me at least £100.

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I'm OK for materials. I have some 3/4" plywood (from stripping out the front cabin on our boat), assorted pots of paint, a very nasty LP somewhere and all sorts of tools. I doubt whether my total 'scope collection would come to much more than £50

Thank you for your post, John, it's very helpful.

Richard

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