Re: [ATM] growing and weaving a tube

[vorblesnak@peak.org]

I have made a bunch of tubes out of various materials.  Wood, plywood,
rigid pink insulation foam, foam core craft board.  I cut the material
with a table saw and glue the joints with polyester glue, (Gorilla Glue,
Elmers Tite Bond etc.)  I strap the tube while gluing up with fiber clamps
and pull it tight.  Once strapped the various pieces can be tapped with a
mallet to line them up prior to the glue setting up.

I like three vane spiders so my tubes are all multiples of 3,  9, 12, 18
sided.  The more sides, the rounder it is.  To set the saw blade I use a
drafters triangle, not the angle guide on the saw.

re: a 24 inch tube ...

Given 20" mirror, 1" of air gap, or two even, a 24" tube would work.
Circumference is equal to pi x diameter
3.1415927 x 24 = 75.3982248  or for my purposes 76"

12 sided tube would yield 6.3" wide slats on the small side, or the inside
as it were.  The outside would be wider.  If you cut 6.3 inch slats and
then trim those to form the tube the tube will be too small. The rough
slat would need to be 7+ inches, depending on the material used.

12 sides yields a joint of 30 degrees, joint face of 15 degrees.  The
joint is made of two faces butting into each other.

If I used very thin material, say 1/4 inch cedar since it is light weight,
I would make the slat with a strong back.  This is a thin piece, perhaps
2" wide running the length of the slat to give it depth thickness.  Think
of it as an upside down T.  The stem of the T sticks up and gives the slat
strength over the length ... though you could make the tube bigger and put
the stem inside.  On a 6" wide slat I would want two strongbacks, two
inches apart.  In a 3/4 inch thick side wall, no strong back would be
needed.

My biggest tube so far was a 20" behemoth, made out of 1/2 inch ply.  It
is 8' long, by nine sides.  This not a tube for your average pencil neck
girly star gazer.  Only manly man astronomers need try and move this
beast.  The tube is about 60 lbs by itself.  I would set up the bearing,
then put the tube in the cradle and then put the mirror in the tube ..
exciting times!  I gave that mirror away, to big.

David Davis
Toledo, OR
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