is this aluminium tube too heavy for a 16" truss?

[fguihen]

Im having a difficult time sourcing aluminium truss tubes for my 16" project.

In Ireland it is very very difficult to obtain aluminium tubing with less than a 1/8" (3.5mm roughly) wall thickness. Im sure this is way too thick.

Ive managed to source 1.25" tubing with a 1.63mm wall. is that too heavy for a 16" truss scope?

any books i have read on the subject recommend a wall thickness of around 1mm.

[TrevorW]

Depends if you are mounting it as a DOB, other option is go with carbon fibre

[fguihen]

its gona be an obsession style dob.

As difficult as it is to get aluminium tube in ireland, Carbon fibre would be even more difficult, if not impossible.

im wondering if i shouldnt just scrap the project if 1.63mm wall thickness is the lightest tubing i can get, as i currently have not spent too much on it. havnt purchased optics or anything like that yet.

[Satchmo]

The standard tubing we use over here is 1.2mm.

I don't see any problem with the heavier tubing as there is not that much of it. If there are balance problems you can just build the top end a little lighter. As an ATMer you can make this up as you go along to suit the project.

[leon]

IMHO, you would be just fine with a tube thickness of 1.63mm, aluminium is pretty light stuff really.

Leon

[PhilW]

Here's one other option: use a six-tube truss not an eight-tube truss, if you're worried about the weight. The scope in the photo has a six-tube truss & it works fine.

One constraint: if you use a full-length light shroud (I don't), then you need to think about keeping it out of the light path somehow.

[rmcpb]

As the tubing is relatively light compared to the UTA and mirror box I would say that 1.6mm wall thickness would have nearly no effect on the balance. Maybe you will have to raise your rocker box a few mm to compensate but it will be RIGID.

Look on the bright side and don't give up!

[tnott]

Yes, you'll be fine. Just add it to your weight distance maths and you can extend the bottom of the mirror box or increase the diameter of your altitude bearings to compensate. 1.25" diameter poles are a bit of overkill for a 16'" but at least it will be very rigid, even with only 6.

[fguihen]

thanks for all the replies guys. il go with the 1.63mm so. i just wasnt sure, with this being my first telescope project.

PhillW, thats a beautiful scope, but im still gona keep it an 8 truss. any plans ive saw or scopes ive been able to inspect have all been 8 truss so rather than go and do something very different, at least until im better at this, il be better sticking to a design im familiar with.

Thanks again for all the advice guys. il post images as i start making the scope ( prob in about 3 months when i have sourced all raw materials!)

[astro_nutt]

Another way is to lighten the tubing by driling a few holes in apporpiate places..
Cheers!!