Friday, June 14, 2013

Weight Reduction Program Again

Now that I am no longer focused on pain, I can resume focus on telescope weight reduction.  The reason that I went with the solid tube was that the truss tube approach failed for two reasons:

1. The lower cage was made of a .125" thick piece of aluminum -- and it was simply not stiff enough.  The truss was incredibly stiff, and exposed that the aluminum was flexing.

2. I stupidly decided that I should minimize weight of the tubes by putting the truss connectors at the very top of the bottom cage, and the very bottom of the top cage.  Because most of the weight of the telescope was the mirror at the bottom of the bottom cage, it enhanced the flexibility problem of the aluminum tube.

The alternative solution is to use the Sonotube with the truss connector at or below the center of gravity of the lower cage.  The Sonotube, after fiberglass reinforcement, weighs .37 lbs/.inch.  The six truss connectors weight 2.6 ozs. each; the six aluminum tubes weigh .23 ozs./inch.  By cutting out 53 inches of Sonotube, I lose 19.61 lbs.  The truss connectors and tubes add 5.85 lbs.  That's a net reduction of 13.76 lbs -- which would get the telescope below 50 lbs -- quite an improvement over what I had before I started the current project, and light enough for the Celestron CI-700 mount.

There remains one uncertainty: cutting 53 inches out of the middle of the tube may create problems with how to mount the Sonotube to the Losmandy dovetail plate.  It will take about 20 inches of mounting plate to attach the telescope to the dovetail plate.  I could stiffen a piece of aluminum C-channel (which would weigh only 2.83 lbs.) by bolting some 1/8" aluminum plate pieces into the C-channel.  Alternatively, I could replace it with a piece of 1/4" steel plate that is only 2" wide (although that would be 6.5 lbs, losing some of the gain from going to trusses).  I can't imagine a 1/4" piece of steel flexing enough to be a problem.

UPDATE: I can't really do anything yet.  I am not supposed to lift any weight until the stent is removed.


  1. You could lighten the sonotube by cuttings lots of triangles out of it, leaving a truss-like structure, but not so much that you make it flimsy.

  2. I could, but I have all the parts, and it would make the telescope more portable, should that be necessary.