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Mister T.
member
Reged: 09/15/09
Posts: 22
Loc: Madison, Wisconsin
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My aluminum tube project is proceeding satisfactorily.
Courtesy of an EBAY seller, I have a sheet of .050" aluminum (6061-T6), cut to size for rolling into a tube. Now to find a friendly HVAC shop with a sheet metal roller to turn it into a tube.  )
I looked for the 6061 alloy because it's supposed to be easy to weld... but a seemingly BETTER idea has come up.
I haven't thought of this for years, but back in the Air Force we had a sort of Red Green solution to any minor problem on airplanes... it was commonly called "500 MPH Tape"!
Whenever it was necessary to make a quick, temporary repair to the skin of an airplane, out came the 500 MPH tape. It's essentially VERY strong duct tape made of aluminum sheet, maybe 2 mils thick, with one HELL of an adhesive on it.
It suddenly occurred to me... if my tube is made with a butt joint at the seam, why not just use two strips of this stuff (one outside, one inside) to hold the tube together?
If 500 MPH Tape will hold the wings together on a hurt C-130, why wouldn't it hold a telescope tube seam together? ;o) And do it a hell of a lot cheaper and easier than welding.
To Be Continued...
Mr. T.
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Owner & operator of the Mahon Loomis Memorial Radio Monitoring Station & Retirement Home for Ancient Irish Setters
Connoisseur of Russian motorcycles, Sports Kilts, Women's Flat Track Roller Derby, and various other eclectic ephemera
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DavidinFL
member
Reged: 08/28/09
Posts: 52
Loc: Navarre, FL
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I don't know how well taping a butt joint would work. I would think that the tube would end up having the cross section of a water drop because the tape wouldn't keep the two pieces of the aluminum tangent to each other. AKA you'd end up with an angle along the seam where the two pieces meet.
Another Air Force idea for you. Have you thought about overlapping the two ends and riveting them together? I'd think it'd be cheaper than welding and would keep the tube round.
Good luck,
David
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Orion XT8 - Orion StarMax 102 EQ
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1164
Loc: Gateshead.NSW Nth Coast,Austra...
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Or using one of those cold eelding epoxy glues maybe and a couple of rivets (one each end) just to keep it all line up and square and aligned while the epoxy is curing.
Of cause 24hr high bond strength Aradite (a two part very strong adhesive) might be just the go....
If it every comes apart , then you'd just scrape it off with sharp stanley knife , and try something else.
Careful with high temp IG welding, it could distort the tube.
Edited by Ian Robinson (09/26/09 03:04 AM)
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Mister T.
member
Reged: 09/15/09
Posts: 22
Loc: Madison, Wisconsin
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Good points, all.
Re. a deformed tube with a "raindrop" cross section:
As soon as the tube is rolled, some "fine tuning" along the length of the joint with a rubber mallet should make the joint tangental, or pretty close to it.
The spider and cell that I'm using here fit over the OD of the tube,and they're more than strong enough to hold the ends in a round cross section.
In addition, I'm planning on putting the focuser right on the joint; it's base and mounting screws should help hold the joint together at a point 3.5" from the aperture.
The mounting I envision for this telescope is based on two stainless steel hose clamps around the tube which will attach it to an oak rail that will mate with a GEM. The clamps will be spaced on either side of the tube's longitudinal balance point by 6 to 10 inches. The pressure of those clamps should hold the middle of the tube in a reasonably round profile.
Adding a slow setting epoxy to the joint before taping isn't a bad idea. After it's sanded down some the tape over it should sufficiently feed my vanity about good looking workmanship; the tape placed over it will give a good, smooth base for painting on the outside, and flocking on the inside.
BTW... during epoxy setting, an improvised jig to support the joint in it's final position seems expedient.
There's a lot that Newbie ATMs building the first telescope have to learn... thanks for all of the good suggestions here!
Mr. T.
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Owner & operator of the Mahon Loomis Memorial Radio Monitoring Station & Retirement Home for Ancient Irish Setters
Connoisseur of Russian motorcycles, Sports Kilts, Women's Flat Track Roller Derby, and various other eclectic ephemera
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Mister T.
member
Reged: 09/15/09
Posts: 22
Loc: Madison, Wisconsin
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BTW... more in line with the original subject of this thread:
I just ran into a possible source of a tube for a BIG (up to 20" ID) scope. Further, the say, over and over, NO
MINIMUM ORDER, and they seem to have a number of surface treatment options. Try this link:
http://www.yazoomills.com/custom-paper-tubes/packaging.aspx
This outfit also has a page to describe a product that I find just a little bit creepy; they call 'em "cremation rollers"! 
They're very high strength (1000 lbs to crush 'em) cardboard tubes that are placed under a coffin to save abrasion to the floor of the cremation retort when ya get slid thru the door!
http://www.yazoomills.com/custom-paper-tubes/cremation-rollers.aspx
An even more intriguing product... would you believe "Blast Hole Casings"?
http://www.yazoomills.com/blast-hole-casings.aspx
THESE look like they'd make a DYNAMITE Dob tube (pun intended)! 
Oh my goodness....
Mr. T.
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Owner & operator of the Mahon Loomis Memorial Radio Monitoring Station & Retirement Home for Ancient Irish Setters
Connoisseur of Russian motorcycles, Sports Kilts, Women's Flat Track Roller Derby, and various other eclectic ephemera
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HandyAndy
professor emeritus
Reged: 01/11/08
Posts: 650
Loc: West Midlands and around
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Hi,
I helped my friend to cut down a tube by 1" to fit in his existing OTA rings.
We used a 1" strip of alloy inside the join to bolt and glue the join to.
We put a couple of bolts at each end.
To hold the join tight while some glue set I planed a convex surface down the length on one side of two pieces of 2"x2" pine. One clamp on each end will apply pressure all down the length as the convex sides are pulled together.
Cheers. Andrew.
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Monarch 8x42, Zeiss 10x50 WA
10mm F2, Pentax 60mm F5
City: 7" MN78: MK4#2, 10" F6.3: MK4#1, 16" F5 ParaCorr
Country: 8" VISAC: (GP2)
Car: 6" F5 MPCC: SP, 5" 127mm F7.5 (GP2)
TV 55mm, Paragon 40mm, UO Pretoria 28mm
B&L 32 Pl, Clave's 25, 8, 6, 2x
Hyperions 5, 8, 13, 17, 24, 31
Nagler1 9mm, Meade 14mm 4000 UWA
Antares 1.6x, 0.7x, 0.5x
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grendel
sage
Reged: 04/12/09
Posts: 243
Loc: Canterbury, Kent, UK
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In the UK there is this company:-
http://www.essextubes.com/
cardboard tubes up to 24" dia
Grendel
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droid
rocketman
Reged: 08/29/04
Posts: 4034
Loc: ohio
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In case anyone is interested, I jus got off the phone with yazoomills, 14inch tube is between 300 and 400 dollars without shipping and a 15 inch is over 400 dollars.
Me thinks I need to rethink this ,lol. 
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102mm Celestron C102HD
Tasco 7TE5 60mm Classic
Tasco 9TE5 60mm Classic
Celestron Ultima 2000 SCT
Remains of an 8 inch dob
Celestron Comet catcher(orange tube)
1960 Edscorp Space Conquerer 6inch f/8
10x50 Bushnell Binoculars.
11T 4.5 inch Tasco reflector Lunograsso?
60mm Telescope Club
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Mister T.
member
Reged: 09/15/09
Posts: 22
Loc: Madison, Wisconsin
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YOW!!!!!
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Owner & operator of the Mahon Loomis Memorial Radio Monitoring Station & Retirement Home for Ancient Irish Setters
Connoisseur of Russian motorcycles, Sports Kilts, Women's Flat Track Roller Derby, and various other eclectic ephemera
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Mister T.
member
Reged: 09/15/09
Posts: 22
Loc: Madison, Wisconsin
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My search for a suitable tube is coming to a satisfactory end.
I find that it's getting harder and harder to find places that can fabricate sheet metal these days.It took a lot of searching and phone calls... but I found a real, old fashioned, Honest to Gawd sheet metal shop, with a set of rollers that can handle a 40" sheet of aluminum!
After getting it rolled into a tube, I discovered that my original plan of using .125" sheet really WAS excessive! It would have been like making a rowboat out of leftover battleship armor plate!
For a 40" tube, 6.625" in diameter, a sheet of .050" is MORE than adequate for mechanical strength; rolling a curve into it makes the tube a whole lot more rigid than a flat sheet.
At the same time, I had a 3.25" wide cutoff from the original sheet rolled into a strip to bolt over the seam of the tube. I figure that a layer of epoxy and some 4-40 machine screws, tapped into the tube wall, should hold things together nicely.
BTW... I think I may have found a simple solution for tube rings for this thing.
Exploring the PVC pipe fitting realm, I found that 6" couplers are a very close fit to the projected outside diameter of the tube.
Sawing a coupler in half and adding a hinge to one cut will make a tube mounting ring. To close it up, a couple of 7" hose clamps around the outside should suffice.
Some modification of the coupler will be necessary; shave out the seperating ridge from the inside, file a cut to clear the seam closing strip, and line the ring with felt strips to keep the ring from marring the tube surface.
At the moment, the major problem is to get some self etching metal primer, and some flat white paint with a high percentage of titanium oxide in the pigment (for the fastest possible temperature equilibrium of the finished telescope).
After that... flat black painting and flocking the interior of this beast are the order of the day. Followed by fabricating a GEM that's heavy enough to handle the weight.
But... that's the FUN (???) of ATM, isn't it?
Next time... start with a mirror that's BIGGER than 5.3" ! At least make the work worthwhile!
Mister T.
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Owner & operator of the Mahon Loomis Memorial Radio Monitoring Station & Retirement Home for Ancient Irish Setters
Connoisseur of Russian motorcycles, Sports Kilts, Women's Flat Track Roller Derby, and various other eclectic ephemera
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