Thursday, May 2, 2013

What Was I Thinking?

Even the reinforcements didn't do the job...and the quotes for stiffer material are pretty horrendous.  So I find myself asking, "What if I used a solid tube instead?"

It turns out that Sonotube (the traditional home telescope maker material) weighs 4 pounds per foot in 20" ID size.  A 6 foot section would weigh 24 pounds; the lower cage, including the mirror and cell, currently weighs 34 pounds.  The tube for the lower cage weighs 6.26 pounds, so the mirror and cell weighs less than 28 pounds.  Adding the Sonotube, the mirror and cell, comes to 52 pounds.  The finder, the diagonal mirror, the spider, and the focuser, weigh about five pounds.  That's 57 pounds.  I would bolt the Sonotube directly to the dovetail (perhaps with a couple supports on either side to prevent rocking), which weighs 2 pounds, 6.6 ozs.  That's still less weight than what I currently have, and far stiffer.  (How stiff is Sonotube?  It is used to pour concrete columns that are 20 inches diameter and many feet high.)

If I fiberglass the Sonotube (a common technique to both improve water resistance and appearance), I can't imagine it would add more than a pound or two to it.  It won't be terribly portable, but big deal -- I don't need to transport it.

I'll go hunt up a 73" length of this tomorrow.  (It ought to fit into the passenger seat of the Corvette with the top off.  I shudder to think what others will think of it.)  I think I became so enamored of a sophisticated portable design that I completely lost sight of the simplest solution.

UPDATE: $49.48 + tax for 6 feet of it.


  1. The fiberglass and resin are going to be heavier then you think.
    The glass is the light part, the resin is another story.