ATM atm re: PVC pipe

[Eric Allen <ericallen@worldnet.att.net>]

Hi Richard.
I have used thin wall PVC tubing (approx. 0.14" wall for 10" tube, for
example) in various sizes for 20 years and have had no problems with
it.  Other people seem to have an aversion to it.  You will get some
reinforcement from the cell, spider and tube collar in any 'scope.  I
have used it in 8" size and smaller, and in sizes up to 14" for fast
'scopes with no additional reinforcing.  I am currently using 2 10"
tubes split and spliced together to make a 20" for my 17.5" f/4.5.  This
is very thin and is reinforced with aluminum on both ends, and in 2
other places where the tube breaks into 3 sections.  In spite of all
this and a somewhat flimsy cell, it almost never needs collimation. 
I've never noticed any vibration.  You can use the schedule 40 (or even
sch. 80, if you have a fork lift), but the thinwall is better.  The air
duct comes in 10 ft. pieces with a bell end which can be cut and used to
reinforce the ends.  I am making an 8" f/8 myself (if I ever finish the
mirror) and plan to use 10" thinwall.  This stuff is ideal for a
portable telescope.  Scraps are cheap.  Try it.
Eric Allen
ericallen@worldnet.att.net
Edmond, OK, USA