RE: ATM Alt Balance and Eyepieces

["KEATING, RONALD J" <RKEATI1@entergy.com>]

> From: Doug Tanaka [mailto:dtanaka@seanet.com]
> I am wondering what other folks do to keep the optical tube 
> on a well-balanced Dob from rising up when removing a large 
> eyepiece - like a Nagler - to put in another eyepiece? 

I've built a 6" f/8 Dob for quick looks and since I use Pentax XL eyepieces
I had the same problem. My solution (similar to Orion's Dobs) was to stretch
a loop of shock chord (bungee chord) over a ball bearing screwed to the
center of the altitude bearing. The shock chord puts tension on the altitude
bearing and the ball bearing is to eliminate any friction so movement will
not be hindered. It works very well.

As for moving your teflon pads, I'd suggest getting some furniture Magic
Gliders which hopefully will be thicker than your teflon pads (so just leave
your old ones in place while you experiment) and place them at various
locations until you find what you like best. Then glue them on with silicone
rubber which holds but can be removed if you later want to relocate them.

Something else to consider, normally on a Dob the idea is to keep the
altitude bearing (balance point) as close to the mirror as possible so you
can have a short base. In our case (heavy eyepieces) this is not such a good
idea, because the distance from the balance point to your heavy eyepiece
will be very long, amplifying the imbalance when the eyepiece is removed. So
to minimize the eyepiece's affect on balance, don't put weight on the mirror
but balance the tube around the middle.