Dobs Mount for C8-NGT

Wanna make a scope? Or better still, grind a mirror yourself. Or, you have some good tips in making a really useful accessory? This is the place to show what your hands can do...
ggodetucsamoht
 
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Dobs Mount for C8-NGT

Postby ggodetucsamoht » Tue Aug 20, 2013 9:46 pm

Hi Guys, just to share some pix on diy dobs base for my 8" newtonian. Tired of typing all the making process hence maybe you just wanna drop me some feedbacks. thanks.

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bornfree
 
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Re: Dobs Mount for C8-NGT

Postby bornfree » Tue Aug 20, 2013 10:47 pm

nice! saw it in action twice! very smooth operation! now thinking if there is anyway to custom make a trolley to pull the base around.. hmm..
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Gary
 
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Re: Dobs Mount for C8-NGT

Postby Gary » Tue Aug 20, 2013 11:31 pm

Please type the making process. :P Just kidding. :)

Awesome DIY! Participants of the recent SAFRA event had a good look of Saturn through it! [smilie=good-job.gif]
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"The importance of a telescope is not how big it is, how well made it is.
It is how many people, less fortunate than you, got to look through it."
-- John Dobson.

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MystiQ
 
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Re: Dobs Mount for C8-NGT

Postby MystiQ » Wed Aug 21, 2013 12:27 am

Brilliant! and very impressive! [smilie=good-job.gif]

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cataclysm
 
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Re: Dobs Mount for C8-NGT

Postby cataclysm » Wed Aug 21, 2013 1:00 pm

Wow, very nice customisation !

ggodetucsamoht
 
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Re: Dobs Mount for C8-NGT

Postby ggodetucsamoht » Wed Aug 21, 2013 9:21 pm

Thanks guys for all your compliments. After some usage I still find somehow the mount isnt perfrom to what it suppose to be. Seems like it cant balance after my telrad and 9×50 finder add on.

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cloud_cover
 
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Re: Dobs Mount for C8-NGT

Postby cloud_cover » Wed Aug 21, 2013 9:59 pm

That's quite normal. You might either want to shift your tube rings upwards if the bottom doesn't hit the ground board or add counterweights to the base.
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ggodetucsamoht
 
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Re: Dobs Mount for C8-NGT

Postby ggodetucsamoht » Thu Aug 22, 2013 10:34 am

cloud_cover wrote:That's quite normal. You might either want to shift your tube rings upwards if the bottom doesn't hit the ground board or add counterweights to the base.


I have tried balancing for normal obs altitude and it perform well, but once come to viewing straight at or near zenith the scope start to fall back and i got to release the tube backwards. As such whenever i need to change viewing angles then i need to readjust the balancing again. If i remove the 9x50 finder then it is able to balance without any readjustment.

I have also come across some specs while designing the dobs mount but to mod it is as good as re-build another set then this unit will be put to waste. unless someone don't mind taking my dobs mount and i can make another new mount. Infact i am more than happy if anyone can get the whole scope from me and i can go for 10" instead..haha

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cloud_cover
 
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Re: Dobs Mount for C8-NGT

Postby cloud_cover » Thu Aug 22, 2013 12:26 pm

Falling backwards as in going beyond Zenith? Then that would be because your tube is backward heavy. I see you have both a Telrad and a 50mm finder (total about 2lbs) bolted on to the top of your scope. When horizontal this makes very little difference but when vertical because the moment of force from the tube itself is almost zero (weight x perpendicular distance from pivot) while that from the Telrad/Finder is significant.
3 solutions:
1. Remove one of the finders. Truthfully you don't really need 2 kinds of finders. Or buy a much lighter red dot reticle and /or a 30mm finder (both on sale by ian, I believe)
2. Add counterweights to the opposite side of the tube. Sounds like you only need to weight out the finderscope
3. Increase the stiction of the bearings. This may require roughing up the bearings a bit or applying some friction material such as felt. Disadvantage is that thick material may cause some settling when coming to the end of a motion, resulting in not quite pointing where you want to, similar to backlash.

Hope it helps! :)
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Gary
 
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Re: Dobs Mount for C8-NGT

Postby Gary » Thu Aug 22, 2013 12:28 pm

ggodetucsamoht wrote:Infact i am more than happy if anyone can get the whole scope from me and i can go for 10" instead..haha


Post a thread in Buy & Sell and state your price. I suspect you may have potential buyers since shipping a 8" inch solid tube dob from overseas will cost quite a bit.
http://www.astro.sg
email: gary[at]astro.sg
twitter: @astrosg


"The importance of a telescope is not how big it is, how well made it is.
It is how many people, less fortunate than you, got to look through it."
-- John Dobson.

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