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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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Been sourcing materials to produce a DIYS carbon fibre tube for V3 of my 10" astrograph , but based on cheapness of rolling a aluminium tube , I'm having second thoughts.
0.8mm x 1.2m x 2.4m Al sheet from Capral (Cardiff) is 69AUD and to get a 1.5m long x 0.306m OD tube rolled from an offcut from the sheet will cost 60AUD (labour only) by Harveys Sheetmetal (Carrington).
Carrington and Cardiff (NSW) are only a short drive away for me , and so no shipping costs , I'd just toss the sheet (precut into pieces that are more manageable , into the back of the Pajero).
Harveys' estimator reckons the tube will hold the shape OK once rolled , but I'll probably get a couple of spot welds to make sure.
Set me to thinking and reconsidering the CF tube project (expensive), since it's going to cost me about 400AUD to make a mandrel , get the carbon fibre cloth and epoxy , and consumeables to make my carbon fibre tube , I may settle for an aluminium tube for V3 of my 10" OTA.
Wwill give a tube 1.27m x 0.31m OD of 0.9kg.
I'm pretty sure with a few reinforcing disks it'll do for mandrel , but as a stand alone unreinforced OTA tube , I'm not so sure.
Aiming at an OD of 308mm to fit my spider and cell.
2mm thick sheet will make a tube of 2.1kg.
3mm thick sheet will make a tube of 3.2kg.
4mm thick sheet will make a tube of 4.3kg.
All of these are considerably lighter than my V2 tube , the PVC tube weighs 11kg.
Must be some aluminium tubed OTAs out there ( as 10" or 12" or 12.5" newtonians ).
What's the wall thickness of the tube ?
How does it perform as far as stiffness and strength is concerned ?
Is 0.8mm thick aluminium too thin ?
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lukasik
Pooh-Bah
Reged: 10/11/05
Posts: 1048
Loc: Lawrenceville, Georgia
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Hi Ian,
try contacting Bird (Anthony Wesley). He's near Canberra, and has made newts with rolled aluminum as you're describing. He's here on CN.
Best Regards,
Bob
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Bird
Post Laureate
Reged: 08/07/03
Posts: 3024
Loc: Canberra, Australia
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Ian, I think the thickness that I have on my tubes is around 1mm, I'd suggest extra strengthening rings on the top and bottom to protect the ends, a couple more internal support rings located wherever you think best. The internal rings should have a collar to add strength, ie they look like baffles :-)
I personally wouldn't go more than 1mm thick on the tube material or the tube might get too heavy.
You might consider contacting Gary Mitchell in Sydney, if you don't know him already. He has a metal workshop near banbstown airport and is very good with aluminium tubes :-)
cheers, Bird
--------------------
Deep Sky Optics 13.1" f/5.5 newtonian,
PGR Dragonfly Express, PGR Dragonfly 2
RedHat Linux + Coriander
http://www.acquerra.com.au/astro/
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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Hi Bob,
thanks for that suggestion, I left a hint for him at IIS , and I see Antony has posted here while I was looking him up in the member list and posting over there.
Hi Antony,
I've seen you posting at IIS on occasion.
I've sketched up something (see attachment) , how's that look fellows ?
I guess easiest way to make reinforcing rings is to have the sheet metal company roll a tube for me that's a bit longer than I need , and to ask them to cut some rings off the end ( or if they charge too much , use the mighty Dremel and the mini cutting disk to do the deed ) and then take a bit out (enough to allow the compressed ring to be slid/ pushed into the tube0 , the compression of the ring trying to spring back will give a bit of extra reinforcement , because the spring force will be acting outwards).
Looks like I might need to buy a Demel circle cutting jig for my Dremel to make fabrication of the annular ribs easier than using my big electric jig saw.
I don't have or have access to a table band saw and that would be the ideal tool to use. I can't justify buying one at this time.
Edited by Ian Robinson (10/16/09 10:32 PM)
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