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Splitting my 12" dob.


JED-E3

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I've decided to split my 12" Revelation/GSO Dobsonian scope. I find it a bit cumbersome to move around, and hopefully if my measurements are correct, I should be able to fit it in the boot of a smallish car with the lower section mounted on the base when finished.

I cut down the base a while ago so it's square with a smaller footprint than standard, but I've not done anything to the tube as yet, so while it's in bits I'm going to flock it, wrap the top section in matt black vinyl, fit an extra finder shoe and move the center bearing up the tube a bit. 

I'll update this thread with my progress, so far it looks like this:

post-26021-0-12510300-1397315824_thumb.j

James.

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To join my tubes, as the two were  too long initially, I cut a 4" length off one of them and then cut a portion out of the resulting ring. This was then carefully fettled until it was a tight fit inside the original tube. I then attached 2" of the ring inside one of the tubes, fitted the other tube to the projecting remaining 2" of the ring and secured both tubes with csk screws. Has worked perfectly well so far.  :smiley:

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Yep, I've used three toggle clamps or over center latches as they're also known.

Peters method sounds nice and simple, my method was slightly less so. I made some hoops from aluminium to stiffen the joint they are rolled from 1/8" thick material but the one edge is 1/4" thick if that makes sense, it's like an angle section with one very short leg.

There is no overlap as such between the top and bottom section but the joint is quite tight and I added some overlapping bits to help align and center the tube.

post-26021-0-00740700-1397422158_thumb.j

I'll add some more pictures tomorrow when I reassemble it all.

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Hi James,

I note in your signature that you have binoviewers. I use mine with my 12" flextube with the trusses not quite extended fully (actually about 10cm from the limiting position) to compensate for the BV back focus requirement. Did you think of getting your BVs to work with your 12" rigid tube scope?

Ed

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Looks a real neat job :)

Is there enough room to move the bearing up the tube to get balance, or will you have to add weight to the mirror end to compensate for the weight of the joint?

The weight of the joint is so close to the alt bearing that I don't think it will affect the balance too much but I have moved it up the tube by about 25mm, I probably could have gone more like 50mm but that wouldn't have left much clearance on the base.

Hopefully I'll have enough adjustment without using counterweights but the flocking is going to affect the balance too..

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Hi James,

I note in your signature that you have binoviewers. I use mine with my 12" flextube with the trusses not quite extended fully (actually about 10cm from the limiting position) to compensate for the BV back focus requirement. Did you think of getting your BVs to work with your 12" rigid tube scope?

Ed

I had thought about having a removable section that I could take out to allow the use of the binoviewers but in the end I decided against it. My 8" skyliner dob has a low profile focuser and almost reaches focus with the binoviewer (without barlow) so i'm going to move the mirror up the tube and use that exclusively with the binos mostly for planetary viewing, and use the 12" for the faint stuff.

James.

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What a really good solution!! Now you get the best of both worlds. :cool:

When I came to measuring up the back seat of my motor for a solid tube 300P I found it was never going to fit. Being a fan of solid tubes over flexi I decided to stick with a 200P but this would have been the ideal solution for me. I bet cutting the OTA got the heart a pumping a bit though didn't it ? :D

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Jed,

Can you please take a photograph of the tubes taken apart? I would have thought some sort of rebate/inner sleeve around the circumference of the tube where it is split would take the strain off the clasps when the telescope tube is tilted.

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Jed,

Can you please take a photograph of the tubes taken apart? I would have thought some sort of rebate/inner sleeve around the circumference of the tube where it is split would take the strain off the clasps when the telescope tube is tilted.

The tube is held under tension from the latches and cannot slide sideways because of the little luggs shown in the following picture.

post-26021-0-06268400-1397507081_thumb.j

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It's basically finished now, I've collimated it and just need to fine tune the balance.

post-26021-0-18731400-1397507256_thumb.j

It's ok with the Telrad and a lightweight eyepiece, I need to adjust it with both finders and a midweight eyepiece.

post-26021-0-60917600-1397507477_thumb.j

It goes together and comes apart very easily, I think having adjustable latches is a must, there's a fine line between too tight and too loose.

post-26021-0-71523900-1397507655.jpg

I'll try and fit it in my car tomorrow, it is possible to lift the base with the lower tube fitted but it's heavy, probably 30kgs, I might fit heavy duty handles to the sides, I also plan on making a solid cover for the lower tube, so I'll add more photos when done.

James.

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