Graphite, Fibre Glass or PVC

[Astroman (Andrew Wall)]

Hi all,

I am thinking in the future to upgrade my Steel tube to a lighter material, anyone know who manufactures these sorts of tubes mine will need to be 254mm dia and 1530mm in length.

All part of the big plan to improve my scope. Before I move upto a 12" for the observatory.

[ausastronomer (John Bambury)]

Andrew,

If you don't want the existing steel tube for anything and just wish to build an identical lighter replacement tube. I would do the following:-

I would use the existing steel tube as a template (mould) and build a new carbon fibre tube. You build it in 2 halves then join them together. Carbon Fibre is similar to fibreglassing where you use the Carbon Fibre Matt then the appropriate resin, excepting of course that it costs a lot more but is also much stronger and lighter than fibreglass. Carbon Fibre actually looks really neat if you do a good job because the gold matt shows through the black resin and gives a really nice appearance and you can polish it to a high lustre. If you have done any fibreglassing at all you should be fine.

Another cheaper option than carbon fibre is to use normal fibreglass matting with vinyl resin as opposed to the normal polyester resin. Vinyl resin is a lot stronger than polyester resin so you could make the tube with much thinner walls for the same strength and thus a little lighter than normal fibreglass. Personnally I would be going with Carbon Fibre, I have seen a couple of Carbon Fibre OTA's and they look pretty smick.

CS-John Bambury

[iceman (Mike)]

I think Bird (planetary/lunar astrophotographer) uses an aluminium tube as it reaches thermal equilibrium quicker and reduces tube currents.. at least that's my recollection.

There's some discussion of it in the last page or 2 of the "show us your rig" thread.

It might be overkill for you, but it's another pov.

[RAJAH235]

Andrew, If you take ALL the bits & pieces, eg, mirrors etc etc, & weighed your steel tube, you would be surprised how light it actually is. Why do you want to change it?
I have added extra lead as counter weights to my t'scope & now the all-up weight,(inc.base,battery,E/Pc. box, etc), is around 40/45 kilos.
It does not move when the wind blows. It has MASS. Solid as a rock.Moves really smoothly, when I want it to. Plus it's a SONOTUBE. ie; cardboard.
If you want a lighter tube. WHY?
L.
Sorry If I've ruffled anyones feathers.
ps. I had been using one of our members t'scopes(10" Bintel) one nite & a puff of wind came up. The t'scope was shaken & vibrated so much that I couldn't see the image.
Just the facts m'am.

[ballaratdragons (Ken)]

I have to agree with Laurie on this one. When I had my mirror out to loosen the clamps, I moved the tube out of the way and was suprised by it's light weight! and mine is a 12". GS use very thin steel. The only thing I can think of is because yours is home-made you may have used thicker steel in the tube than necessary.

[Astroman (Andrew Wall)]

The main reason is with mirrors, focuser, finder on the tube weight is 15kg But this includes the dob Alt axis aswell. I just thought a fibreglass or other material tube would lighten the load, so I don't have to lug around so much weight. I am having problems with my Back right now and finding it difficult to carry the load. The material used on the tube is quite a bit thicker that the GS scopes I have seen. It is rolled galvanised steel, not sure of exact thickness.

Maybe I have not thought this through completely, and just giving myself an extra expense that I really don't need now (saving for an eq6 with skyscan)

I appreciate all your comments, it gives me a better understanding of where I should go.

Thanks

[slice of heaven]

For a comparison Astroman,
I have a fibreglass 8" OT. It weighs under 10kgs. Thats complete with no finder. It's an F6 though so the tube is 200mm shorter than yours.
Might be an expensive excercise for a couple of kilos.

Slice

[Orion]

Here is a link about making fibreglass telescope tubes if your interested.
http://www.atmsite.org/contrib/Kohut/fgtube/page1.html