Rolled aluminium tube

[paul11]

Hi all I’m making an 200mm newt and I want to get an aluminium tube rolled, what is the best way to join the tube. Can anyone show some images of how you did yours,,,,,Paul.

[leon]

Paul, I'm sure you are a handy person and would like to try this your self, however rolling a tude especially in Aluminium is pretty tricky work, and unless you have the equipment to do this it would be easier, with a better result if you had the professionals do it.

They have special tools for this sort of work, and it will save you a lot of heart ache.

The best places to go to are, places that specialize in sheet metal fabrications, and makers of, one off customer requirements.

leon

[Ian Robinson]

I looked at doing the same thing for my 10" OTA rebuild , the join needs to be welded.
I was going for a 2mm think tube.
I had lined up a machinist who specialises in aluminium work , has a tube rolling machine .... was not going to be cheap.

I eventually ditched the rolled aluminium tube idea for a plastic storm water pipe that I got as an offcut for nix (from a friendly building contractor).

You are in the UK, why don't you ask Beakon Hill or Orion if they can sell you a tube, or do what I did , ask a contractor at a building site if he has an offcut of suitable OD and length that he can spare.

[paul11]

Thanks for your help guys I think I’ve need to do a bit more research on this one but I will let you know how I get on,,,,Paul.

[firstlight]

The first tube for my 10" was rolled aluminium in 1995. I had it done at a metal fabricator and welded by a local (at the time) engineering firm... pretty tricky to weld ali without warping... boat fabricators may be your best bet.

Aluminium will conduct heat excellently, which will mean you will be introducing tube currents every time you get close to look through the eyepiece. The Amateur Telescope Makers of Queensland spent a lot of time debating and testing various materials to eliminate thermal currents and found that wood is the most thermally inert material... this is readily available in a refined form as cardboard tube. Can be pretty heavy though depending on the wall thickness.

If weight is the issue perhaps a truss style tube is the go. Hope this helps.

[gbeal]

I did an 8" mirror tube a while back, piece of cake.
Went to a local sheet metal man, and he sold me the sheet alloy, from memory it was 1.3mm? thick, but there is varying thicknesses.
He rolled it to the diameter I wanted, while I waited/watched.
Cost was negligible, OK, not as cheap as a free off-cut of PVC, but reasonable.
I contact adhesive glued the butt overlap. The tube is effectively held by the mirror cell attachment screws as well as the glue join, and the front is the only "weak" link. Never experienced any problems at all. I baffled the inside though, front to rear, and these glued in baffles "may" have helped a little, not sure.
Gary

[snowyskiesau]

There's always the timber alternative (http://users.tpg.com.au/users/daveg/Tube.html)

About half way down the page, there's a weight comparison between wood, PVC and cardboard (sonotube)

[mick pinner]

if you get it rolled with a 10mm recessed edge along one length so that the outside diameter remains the same all the way around you can then glue the overlap with 3M PANELBOND, available from automotive paint suppliers, WHEN CURED IT IS A STRONGER JOIN THAN SPOT WELDING.

[paul11]

Thanks again guys for some great ideas, the timber alternative really looked an excellent way to form a tube. I have found a local firm that can roll me a tube out of 1mm or 1.2mm aluminium I am going to see them on Monday about cost etc I will let you know how I get on,,,,,Paul.

[cfranks]

When we were making our Dobs 8, 10 and 12", we used spiral wound steel airconditioner ducting. I can't remember the exact gauge but it was about 1mm and therefore fairly light. Certainly lighter than 10 or 12" plastic sewer pipe.

Charles

[Astro78]

here's a good benchmark for an aluminum tube

http://www.acquerra.com.au/astro/equipment/13/

[Satchmo]

Speak of the devil, I was just talking to the maker of that tube ,Garry, 5 minutes ago . He has a sheet metal construction business and is a long standing amateur astronomer owning scopes up to 20 " F5 . PM me off list if anyone is interested in services. He also makes superb mirror flotation cells for both truss Dobs and round tubes `scopes at very reasonable prices.

Its rare to find competent tradesman who have real sensibilties as far as astro gear , and he'll always suggest an improvement in your design if he can see it.

[Astro78]

Garry's currently working on a 12" tube for me now! Can't wait and love the idea of the two piece for easy transport. With a conical mirror on order from Royce (damn AU$!) should weigh in nice and light.