ATM Re: atm-digest V1 #299

[BUDDYDIGS@aol.com]

In a message dated 96-08-16 02:16:46 EDT, you write:

>>  
>>  I'm considering making a square main tube out of 3/4 in. treated plywood.
>> I've drawn the design to have the inside of the square measure 12in.
(10in.
>> mirror) This would require a secondary mirror to be roughly 6 3/4 inches
>> from the bottom of the focuser. Is this too far? In other words is there a
>> focal length between the eyepiece and the secondary that must be measured
>> correctly? If so, is there a formula to calculate this distance?
>> Thank's, Jim
>> 
>> 
>> 
>I would use 1/4" plywood with say 3/4" wood strips to hold the corners
>together. You will find the 3/4" plywood tube to be very heavy.
>
>

Hi all

Been enjoying everyones posts!

Just recently finished an 8 f 5 scope, and I made  a  wooden square tube that
is 12 inches on a side by 4 feet long.  I used 1.5 inch by 1.5 inch white
pine strips running the length of the tube in the corners and  3/16 inch
thick birch? plywood for the sides. the plywood was attached with wood glue
and screws.  The front and rear end of the tube had .5 inch thick plywood
with 10 inch circular holes for additional bracing. With some additional
braces (which could also double as baffles) located around the side bearing
area, I think that would be the stiffest tube anyone would need.  3/4 inch
would be horribly heavy as mine is about as much as i would want...

Buddy Welker