From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


>From: Orion105 
>
>I have completed the build of the OTA of my 12.5" f/5 Dob.  I am now
>finalising the alt bearing size and position.  I would like to use a
>range of EP's that include my 20mm Nagler which weighs over 2 lbs and
>also some regular Plossls.  The calculated CG position varies over a
>range of close to 2" depending on which EP I will use!
>
>So, for the bearing size and position what should I assume?
>
>I could position the bearing for the mid point of the cg range.   Would
>static friction be enough to stop the scope tipping both up and down
>depending on EP used?
>
>Or I could position the bearing for the lighter EP and place removable
>weights on the UTA for the time I use the big Nagler?
>
>What's your advice?
>
>Ado

Hi Ado
 It would be better to have smaller weights to add at the
eyepiece end when not using your Nagler. Still, on a 12.5" you might
find that there is enough friction to make up for the slight differences in
balance. You have a lot more problems on a smaller/lighter OTA. There are
also some tricks that can be done with springs, instead of weights.
Dwight

--- BBBS/NT v4.00 MP