Re: ATM Sonotube is good for making cement columns...

[Bruce Swayze <swayze@europa.com>]

At 08:06 AM 7/15/97 -0400, you wrote:
>Why is everyone looking for Sonotube?  It is cheap (but often it looks
>cheap)... it is heavy.... it is often covered in wax... it is paper and
>absorbs holds moisture... the spyder may collapse the tube without
>reinforcing, etc.                  <snip>

The tubing from Apogee sounds great, and it's good to have another option.  
However, I just wanted to mention that for those who can't afford it or
don't want to spend that much, sonotube remains a very good option.  I used
an 18" sonotube for my scope that I built in 1981, and it lasted me fifteen
years, and would have probably lasted another 15.  The exterior-grade
plywood I used for the mount was delaminating and coming apart before there
was any visible damage to the sonotube.  It all depends on how you finish it.

I used a flame from a blowtorch to flash-melt and burn off the waxy coating
from the outside of the tube.  If done carefully, you won't burn the tubing.
Any minor scorched spots can be sanded a bit before painting.  The inside is
usually wrapped with a shiny plastic material that is spiral-wound onto the
paper surface.  You just grab the end and begin pulling and it comes right
out.  

I then soaked the entire tube, inside and out, with a good exterior grade
primer.  Then the inside was painted the traditional flat black with a
couple of coats, and the outside was painted with 3 coats of marine-grade
boat paint.  Your tube will last forever if you do this.  I used it on
countless nights where it was soaked with dripping dew, covered with frost
like a fuzzy blanket, or baked during the hot sun during the day.  I never
repainted it either.  

For the spider, I didn't have a problem with tube deformation.  Just don't
pull too much tension on the vanes.  Another option would be to reinforce
the tube near the spider with a narrow plywood ring.  

Sonotube remains a viable option, but thanks for the great tip on the Apogee
tubing!

Bruce Swayze
swayze@europa.com
http://www.europa.com/~swayze    Swayze Optical home page
http://www.europa.com/~swayze/spider.html   Homemade spider page