Aluminium tube?

[garymck]

Hi,

has anyone managed to source large diameter aluminium tube (say 10-12" diameter) suitable for telescope tubes here in Australia? Have done numerous searches but been unable to find any. After proper tube, not rolled and crimped or welded tubes which are never truly round.

cheers
Gary

[iceman]

Bird (Anthony) has an aluminium tube - I'm not sure if he got custom made but he'll probably reply here when he sees it.

[snowyskiesau]

Largest diameter aluminium tube that I've seen available is around 200mm. This typically has a wall thickness of 12mm which works out to be (about) 20 kgs per metre.
I don't know which state you reside in - try Onesteel, they have branches in every state.

[gbeal]

Does it have to be aluminium? I have used rolled alloy tubes, with the crimp/join, and know what you mean.
Recently I built a carbon fiber tube (for the 10" f5 newt), and haven't looked back. Maybe worth a thought.

[garymck]

how hard was it to make the tube - have never worked with carbon/glass fibre before? Did you get it very round? Have a pic?

cheers
Gary

[Garyh]

Hi Gary,
I found it very hard to find any suitiable tube at all. Not even PVC pipe in 8" size for my newt. Had to get the local enginering place to make up a aluminium tube for me. They did a ok job on it but the tube is not exactly round having to put fold lines on each side of the weld and took me ages to get the tube close to round..and smooth...(auto body filler)
I would be interested where you can buy good tubing as well or how to make a carbon fibre tube and supplies?...:shrug:
Cheers Gary

[asimov]

When I was making my 12.5" newt I was advised to approach Parks Optical in the States to get the 16" tube I wanted. Of course I never did. I made my own out of a sheet of 2mm ally & rolled it myself.

[asimov]

The next tube I make will be out of fibreglass I think.

[bird]

Gary, I have 2 aluminium tubes made by Gary Mitchell in Sydney. He runs a metal fabrication workshop near the airport. He rolled a 12" tube for me that I used to hold a 10" mirror, and he's also rolled a 16" tube that I'm using to hold a 13.1" mirror.

You can see photos of the 13.1" tube here:

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

They are fantastic tubes, the end rings make them very sturdy and they are light as well.

cheers, Bird

[gbeal]

Gary,
it was difficult, being the first one I had made, and it was done with an "expert" mate who had done some fibreglassing before. In simple terms it was a matter of building a suitable former to wrap the resin and fabric around. A layer of foodwrap film to allow separation once the resin had set, and then layer of resin, layer of matting. The matting we started with was Kevlar, but it wasn't stiff and hard, but more slightly flexible, so another layer was added, this one being C/F.
In the end I slipped a thin layer of fibreglass on the inside ends, where the most stress was going to occur, to stiffen it further.
Once set I made tube baffles from old formica laminate, and glued these in place. They were mainly to provide contrast etc, but I knew they would also add more stiffness. There are about 10 of them, plus a swag opposite the focuser.
Work? Yep, I am happy with it, and previously the tube (sono-tube) complete weighed in at about 14 plus kilos. Now it is about 10 and a bit.

[garymck]

Hi Bird,

tube looks very nice, however, I'm trying to build a rotating tube that will still stay orthogonal for accurate gotos. My current 10" Skywatcher newt is a steel tube (rolled and crimped) an suffers from 10 not being round so that rotating the tube causes my pionting to go to hell, and 20 is way too heavy (the scope weighs about 16kgs). Want to save weight and be able to rotate tube without loosing goto accuracy.
gbeal (http://www.iceinspace.com.au/forum/member.php?u=42), your tube I think will be beyond my ability with no prior experience. May try a Protostar tube - very light and not too expensive.

Thanks all you guys for the constructive suggestions,

cheers
Gary

[bloodhound31]

How about a 44 gallon drum with the ends cut out!????

Baz:D

[astro_nutt]

Please don't laugh but I have considered using a tube insert from an old gas hot water heater that people discard on their naturestrips during hard rubbish collections..some of them are quite sound although made out of steel..just in need of a clean-up and a coat of paint..I would cut-out some plywood rings with a router and glue-screw them into the tube...maybe one day!!

[Gama]

Ask they guys that do the Air con/ Ducted heating for factory installations where they get the tubing.
You can get them quite large, and they are galvanized as well.
Large Air con mobs buy them from somewhere, so should you.

[garymck]

Hi Gama,

thanks for the suggestion, but aircon ducts are steel - so no weight saving over my current setup and the tubes are rolled as well so still slightly out of round.

cheers
Gary