RE: Re: ATM 6" Dob: How Easy? How Cheap? How Heavy?

[Don Loftus <dloftus@edu15.coe.ufl.edu>]

Brent Hutto wrote:
(SNIP)The prevailing opinion seems to be that 3/4" plywood as specified 
in the SF Sidewalk Astronomers plans could probably be reduced somewhat 
on a 6" f/8 scope but solidness and stability is necessary and a 
>reasonable weight could be maintained with something close to those 
specifications. Also, putting screws into thinner plywood doesn't always 
work out well. (SNIP)

Brent,

I'm sure others have given you this advice also, but in case they 
haven't, here is my 2 cents worth.  For a 6" you could really use 1/4 
inch plywood with a 1x1 spruce frame on the edges to give it rigidity.  
Cut your altitude bearing surface for the box out of 1/2 inch plywood 
(or two layers of the 1/4 inch plywood) in a semi-circle about 1 to 1.5 
inches wide and glue to the 1/4 inch plywood sides, which have also been 
cut in the same semi-circle size to match. This will give you 3/4 inches 
of surface to mount your Teflon pads for the altitude bearings.  The 
base boards will probably have to be at least 1/2 inch plywood to keep 
from flexing.  All plywood should be hardwood and without voids.  It can 
be expensive, but is the best building material.  Paint everything well 
to seal out moisture.  

Remember, it is the glue that is doing all the work, not the screws.  The 
screws only hold the wood in place until it dries.  You may want to 
substitute small brad nails to hold while the glue sets.  

If you want more weight while observing, make some weights you can attach 
to the framework.  That way you can remove it when you don't need it and 
won't have to lug it around while setting up.  You could use steel 
plates, concrete stepping stones, bags of lead shot, etc.  Hope this 
helps and I'm being clear.

Don Loftus
Gainesville, FL