Small (150mm) open truss pros and cons

[CharlP6 4]

While still waiting for my mirror, I'm looking at materials to build the scope, especially the tube.

I'm starting to play around with the idea of an open truss since large enough PVC pipes are rarely available in lengths less than 6m and I'm really not fond of the idea of using a cardboard tube.

All of the normal considerations for building a truss is irrelevant at this size and I can think of a lot of cons. I do think it would look cool though, and I don't think I've ever seen such a small open truss scope.

Why would you encourage or discourage the construction of such a small open truss scope?

[Peter Drew 11,211]

It can be frustrating not having suitable materials to make a conventional tube, a truss tube can certainly provide a workaround. I have a 6" truss tube Newtonian that I built as a rough plan prior to making a 30". There is quite a bit of work involved at any aperture but it does look cool. I won't try and add to the list of cons that you have identified but to be honest a wooden square tube for a 6" has a lot going for it on pros. Easy to make, cheap, available materials, the square section simplifies fitting components and also discourages the circulation of tube currents. I could go on.....  

[Alien 13 7,372]

There are quite a few positives with a truss tube..

It looks cool.

Easy cool down.

No tube currents.

Easy clean with a quick blast of CO2.

Alan

[ronin 3,800]

[ronin 3,800]

Someone here on SGL built this the post was a couple of years ago now. I fancy having a go at one if I even get a long focal length 150mm mirror, the 1200mm variety. I did ask if any plans existed but it was done somewhat by trial and error. Kept a few of the images.

It is/was a 6" but built as an ultra portable, not a kind of permanent truss.

Edited June 20, 2017 by ronin

[Chriske 1,669]

I'd go for a truss..

[CharlP6 4]

Thanks for all the replies. It's reassuring to know that I am not completely crazy. @ronin, that's a really awesome design in the picture, I have something similar in mind for the truss, but I don't think I'll go for the dobsonian mount. Next is to decide if I want to be able to disassemble it or keep it permanent. Permanent will be less work, but portable is novel.

11 hours ago, Peter Drew said:

I won't try and add to the list of cons that you have identified but to be honest a wooden square tube for a 6" has a lot going for it on pros. Easy to make, cheap, available materials, the square section simplifies fitting components and also discourages the circulation of tube currents. I could go on.....  

I've seen few wooden "tube" designs in in octagons and squares etc. and to be honest, I don't really like the look of it, but you're absolutely right, a square assembly will make a lot of tasks a walk in the park, like mounting the focuser and secondary mirror.

I am curious as to what effect an enclosure has on the view quality. People go through painstaking effort to blacken a tube's inside to get rid of stray light rays. With a truss you allow even more strays in, or is there something I don't completely understand?