5 replies to this topic

[DrSteve]

I bought  a roughly 10 1/5" O.D. by 48" long cylindrical fiberglass water tank at Habitat for Humanity for a different hobby use, but looking at it, I wondered if it could be used as a tube for a DIY refractor.  It seems to be too large for the commercially available 8" mirror cells and too small for the 10" ones.  I have not seen any commercially available 9" mirror cells or mirrors.

 

Anyway,  my question is whether a fiberglass tube of this size has enough value to be reused as a scope tube, or whether it is better to forget the whole idea.

[Phil Perry]

No reason you couldn't use it for an 8" cell -- it sounds like it's going to be too small to fit a 10" mirror (what's the I.D.?). Probably a little short for an f/6, but f/4 to f/5 should work. If you have no other use for it (including resale), it's better than nothing. More ATMs either use Sonotube (circular cardboard forms for pouring concrete footings) or build a truss -- I think both would be lighter than fiberglass. Just be careful cutting and drilling fiberglass -- those fine glass fibers are not something you want in your eyes or lungs. Or on your skin, for that matter (very itchy). Presumably there are paints that will stick OK to fiberglass.

[dan chaffee]

It will work. What I don't like so much about fiberglass

as a tube material is that it stores heat longer than an

aluminum tube of the same stiffness. I had a 10" f7 in

a fiberglass tube, even with vent holes

in selected positions and would not repeat that experience.

even sonotube will equilibrate faster than fiberglass..

[Dan Watt]

I design my 8" scopes to have a 10" ID tube. Really helps with thermals and having a bit of space around the mirror for adequate side support. But fiberglass? Ick, if I can get through life without ever having to work with fiberglass again I'd be happy. My forearms are itching from here.

[Pinbout]

i always make my tube 2" larger than the mirror... just cut some 3/4" ply like.... 

 

its just a truncated triangle. 

 

[ccaissie]

a tube for a DIY refractor.

You must mean reflector....

How thick are the walls? 

sounds good for an 8" f/5 or so.  Might need a slightly larger than optimal secondary because of the 1" clearance, but should be ok.