Dobbie Wobble :)

[vindictive666]

hello


i was wondering if anyone else that owns a dob that gets a bit of wobble when you knock it (shake it) (not hard) would the bearings be the cause?
ive only just started to notice it
it can be a bit of a problem at high mag :)

it settles reasonable quick though :)

the centre bolt is tight enough

hmmm another little puzzle to cure :)


i also forgot to mention that my base(with 3 legs) is of a triangular contruction and not round like the dobs base if you know what i mean :)

[toetoe]

I don't know anything about dobs John, i would have thought that the length of the tube may cause a slight wobble though. Sorry to speak out of term but that's just a thought i had. :)

[slice of heaven]

Wobble in a gs dob? :scared: unheard of
http://www.iceinspace.com.au/forum/showthread.php?t=1294
IceInSpace Forums - Dampening on gs dobs

[janoskiss]

My 8" seems to have gotten more wobbly over time (or I've become less tolerant). It is annoying at high mag, when you have to nudge the scope every 5 seconds to keep a planet in view. The vibrations take a couple of seconds to settle, which does not leave much time to get a good look. Focusing is tricky business too.

I think it would not be a problem if the motion was smoother, less stiff & sticky. I've been looking at doing something with my alt/az axes; fitting rollers / bearings / sliders /grease ???. Haven't made up my mind what would work best. There is also too much flex in the sidewalls of the mount so I've been thinking about making a new mount from plywood, but that would be going against the Minimum Effort Principle.

[Starkler]

Just to put things into perspective, how much wobble would you expect if you spent the same money on an achro refractor+cheap eq head+aluminium tripod ?

[janoskiss]

My first scope was a 4.5" (114mm) f7.9 reflector + EQ + tripod from Dork Smith (had to change the spelling because D got filtered!!). I paid $200 for it; but you'll see the same sort of scope for twice that in camera shops, which is what I paid for the Dob. (You can check out the DSE marvel here (http://www.dse.com.au/cgi-bin/dse.storefront/42d08de000a72a6e273fc0a87f9c0740/Product/View/L8258).)

In light wind, the scope was near unusable at 100x because of the constant vibration, and completely unusable at 150x. In nil wind, 150x was doable but the optics was breaking down.

It is virtually uncollimatable because the spider is fixed and the diagonal always ends up off centre. Terrible contrast because the central obstruction is huge and spider vanes are thick. No Cassini division in that nasty piece of work.

I use the mount now with an old 60mm refractor I got off ebay for $25. That little scope outperforms the 114mm Newt by a long shot! The mount still wobbles but it's usable with the featherweight scope.

Hey, ... maybe I should write a review for the DSE Newt, to warn people off buying such rubbish??

Ah, and with the Dob the vibration is just annoying at 300x and not really a problem at 150x.

[ballaratdragons]

I don't know why, but I hardly get any wobble on my 12" Dobbie! Too heavy maybe?

[Dave47tuc]

I found with these Dob's that if i was set up on unstable ground or grass, the mount was wobbly.
So I went to the local garden supply shop and brought a 600mm round 2" thick concreate paver.
I have put that in the ground and leveled it. The scope is a lot better on the paver, a lot more stable :thumbsup:

Mind you i can't take the paver when I'm observing in other locations.
I'm not that strong :P

[slice of heaven]

Depends what the individuals acceptance level is.

[slice of heaven]

The side panels are too flexy on the 12" gs dobs, they need bracing or replacing.

The 3 toed ground board is too thin and weak.Needs replacing with a 30mm heavier density board ..circular..and 4 lower profile feet.

Chuck the bearings , or make a lazy susan for the dinner table out of it , and fit teflon pads.

Thats the 3 main areas that need addressing. Fix 1 and the other areas will let you down.

[ballaratdragons]

I did the teflon bit. Works a treat. I am tossing up between making a 'you-beaut-fang-dangled-fancy' dob mount or an EQ mount. Either one will be an improvement on the factory one.

[Dave47tuc]

Some pics

[Chrissyo]

My dob got a bit of a wobble this afternoon (took it out at 4.40 or so to see Venus :D ).

Have you checked the Altitude circular things which rests on the base?? (can't think of what they're called?) One was loose on mine resulting in a bad wobble. Due to my own stupidity I made it worse by seeing what would happen if I unscrewed it fully, not thinking there would be a washer and nut inside, which I had to fish out and remove the mirror cell to screw back in. :P :ashamed:

[ballaratdragons]

Aaaah! We live and learn Chrissyo!

You Know it happened to make you re-collimate your scope. LOL