UK Source for 10” welded seam aluminium tube?

[markse68]

I was having a go at Sirius last night to see if I could see the Pup- I couldn’t ... But in the process I came to a rather disturbing conclusion! I’d been out for quite a while- maybe 45mins so the scope should have cooled sufficiently though it had come from warm flat to icy cold night here in London. As I worked my way up through my eyepiece magnifications I was a bit disappointed in how not point sourced Sirius looked. Eventually I reached my highest power ep- my lovely Nagler 4.8mm type1. It was out of focus when I put it in and I saw something I’d not noticed before. Credit to my new  secondary which seems to have made a big improvement I could see for the first time beautifully sharp diffraction rings in the Airy disk- but they were swimming like a psychedelic light show at an early Pink Foyd gig! Quite mesmerising and I was enjoying them for quite a while but I’m fairly sure this was due to tube currents and not a good thing! In fact I’m wondering if they were contributing to the poor seeing and astigmatism I was getting at high powers that lead me to buy a new secondary in the first place 🤔

So to help remedy this I think I’m going to change the tube to aluminium. Aluminium must surely be the best material for a Newtonian tube- it can be quite thin and light and still be very rigid in tubular form but more importantly is an excellent thermal conductor with low thermal mass so should reach ambient quicker than any other material and offer less insulation to the interior of the tube- certainly a lot better than the pvc drain pipe I currently have! A fan would help too of course. 

Theres a company in the US called Parallax who make superb looking traditional newts and who will supply tubes to diyers but I hate to think how much freighting a tube that size to here would cost.

So I’m looking for a uk supplier of aluminium tubes- preferably seamless or at least welded rather than folded seam- anyone know of such?

Edited December 2, 2019 by markse68

[JOC]

11 minutes ago, markse68 said:

they were swimming like a psychedelic light show at an early Pink Foyd gig

That sounds like Sirius all over and might be a factor of the amount of atmosphere you were looking through rather than anything to do with your tube not being cool enough.  In fact Sirius is notorious for looking like that.  In fact my son and I call it the monster raving party star for that very reason - it looks like a spectacular disco ball.  It is entirely possible that you might change the tube for nothing.

[markse68]

Ok but would it’s unstable nature cause the diffraction rings in its unfocused image to dance? Fairly sure that was tube thermals as I could distort them by putting my hand on the edge of the tube inside the aperture, and to double check it wasn’t atmospherics I pointed the scope straight up and found a star (🤷‍♂️) near zenith and it had the same effect 

[JOC]

From what I've read on SGL to see Sirius in a calm and viewable state is actually the exception rather than the norm.  If everything else you are viewing looks OK, I would venture that the temperature of the tube must be OK and its just Sirius being monster raving looney Sirius?

[Peter Drew]

Sirius is far too low from the UK to present a decent telescopic image other than on rare occasions as JOC has said.  If Sirius shows any scintillation to the naked eye it will look far worse in the telescope.  An aluminium tube should be better than a plastic one for several reasons but you are unlikely to find a supplier of large seamless ones.  A metal fabrication firm should be able to roll, weld or seam a tube for you but it is likely to be expensive.   🙂

[Rusted]

Unless you are committed to aluminium tube you might enjoy thin galvanized steel ducting. 
Not the usual spiral stuff but with a single long, straight seam and smooth elsewhere.
A tiny, radiused flange stiffens both ends without need for anything added. Handy for retention of large objective cells!

Sold mostly for woodworking factories. Or where any potentially inflammable dust collects in the dust extractor system.
Available up to at least 16" in diameter and probably more.

I get mine off the scrap heap behind a local furniture factory for the price of a pint per 2m length.
The seam fits nicely in Skywatcher type tube rings at the hinge gap.
I have used the 8" tube for my 7" refractor and it looks authentically Edwardian. Doesn't mar like paint does.

I also have a 2m length of 12" waiting for my classical 10" f/8 Newtonian with premium mirror.
Another roundtoit.

No greater weight than aluminium in the thickness you'd have to use anyway. 
Never really rusts and is only 1/3mm in thickness. Wonderfully stiff and never needs painting!
I took the conical adapter for making a pier but have never used it.

[Oldfort]

How about this company?

http://www.tubesupplies.co.uk/aluminium.php

[markse68]

Thanks very much Oldfort- I didn’t find them in my search- will contact them about pricing