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Old 01-27-2009   #1
 
Groveland, California
Join Date: Nov 2008
Posts: 177
Advice on Bending 6061 Tubing....?

Hello all,

I am new to the forum, though I have been lurking for a while.

I recently purchased a 14' raft, and am starting to build an aluminum frame for it. I have a really nice rotary draw tubing bender with 1.5" and 2" dies. 1.5" seems a bit small, so I am planning to use 2" x .125 wall tubing for the main (perimeter) structure. I have searched on the internet and forum for information on bending 6061, and while it sounds like many have done it I couldn't find any specific info on technique, using heat etc. The manufacturer of my bender says it is possible, " but be careful because it might break." (The tubing...not the bender...)

Has anyone successfully bent 6061 tubing of this diameter? If so, I would greatly appreciate any tips before I purchase the material and get to work.

Thanks,
Guy
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Old 01-27-2009   #2
 
freexbiker's Avatar
 
B.F.E., Wyoming
Join Date: Jul 2005
Posts: 912
Chip would be your guy I think. The tinkerer of the site.
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Old 01-27-2009   #3
 
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Denver, Colorado
Join Date: Oct 2003
Posts: 75
I have not worked a great deal in Aluminum but I do have some experience in that material and 10 years in metal fab work over all.

I think you will be ok if you use a plumbers torch to LIGHTLY heat the material and DON'T try to bend 90degree angles. Do 2 45s and weld them together to make your 90.

I hope it works out for you
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Old 01-27-2009   #4
 
Groveland, California
Join Date: Nov 2008
Posts: 177
Hmm, I didn't think of the two 45s approach...that might work if there is enough room for a second bite on the bender. If not, and I have to weld joints in every corner, I would probably just by mandrel bent 90 elbows from here:

Bent 90° Pipe & Tube Elbows with Two Tangents on Sharpe Products Inc.

but for strength, asthetics, less weld joints (and a challenge), I would prefer to bend the entire perimeter from two mirrored "j" shaped lengths of tube.

Yeah, plumbers torch is what I would try. It is amazing what a little heat can do to increase the pliability of aluminum.

Thanks for the tips!
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Old 01-27-2009   #5
no tengo
 
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Baytopia, Colorado
Paddling Since: 1876
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try 6063 instead.
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Old 01-27-2009   #6
 
Groveland, California
Join Date: Nov 2008
Posts: 177
6063 would be ideal, and is readily available in pipe sizes, but hard to come by in tubing. I have to stick with tubing that fits my dies, or go with the weld-in-the-corners approach.
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Old 01-27-2009   #7
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Baytopia, Colorado
Paddling Since: 1876
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pipe is cheaper than tubing. maybe you could buy a pipe sized die. if you use 1.66 OD your frame will be NRS compatible and if you use 1.9 OD your frame would be DRE compatible. this would be a possible selling point or if you were in a pinch for a spare part.
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Old 01-27-2009   #8
 
C. Springs, Colorado
Join Date: Aug 2004
Posts: 1,106
I use to be an aircraft mechanic and know a little about bending aluminum. ........more than likely you will create stress fractures when you bend aluminum of that hardness. Best bet is to use something softer to start with or you will end up waisting some expensive tubing. Heating it with a torch while bending it will work, as heating does soften it, but you willl still need to reheat treat it after. The proper way to do it is to start with softer tubing and have it hardened through proper heat treating to get it to that hardness once you get it bent to the shape you want. We use to use a digital/programmable furnace at Continental Airlines. I'm sure there is someone in Denver with the proper equiptment.

You might not need to heat treat it at all if you start with something softer like 6063. Good luck.
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Old 01-27-2009   #9
 
Join Date: Jul 2006
Posts: 211
Frame

If you are set on bending the corners then you need to go with a 5000 series tubing. I use the T6061 and speed rail fitting that you can get at Aviation Industrial Supply in Denver. Just make sure that you get you coolers and boxes first so you can build the frame around them. A chop saw with a fine tooth wood blade work well to cut the tubing. Wear Eye Protection. Good Luck
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Old 01-27-2009   #10
 
Groveland, California
Join Date: Nov 2008
Posts: 177
Wow, thanks for the replies!

Quote:
Originally Posted by mania View Post
pipe is cheaper than tubing. maybe you could buy a pipe sized die. if you use 1.66 OD your frame will be NRS compatible and if you use 1.9 OD your frame would be DRE compatible. this would be a possible selling point or if you were in a pinch for a spare part.
I thought about this, but changed my mind when I checked pricing...$300 for a set of dies. Quite a bit more than when I bought the machine years ago.

Quote:
........more than likely you will create stress fractures when you bend aluminum of that hardness.
Very good point, and this hadn't crossed my mind. I am guessing that this is a good reason to scrap this approach. Very likely the cracks wouldn't be visable until it was too late. Thanks for mentioning this. When I found the commercially available 6061-T6 elbows, I just assumed it would be possible to bend the material myself...It didn't occur to me that they were bending them in the "O" condition and then heat treating them.

I am an A&P also. I worked in General Aviation up to about 6 years ago, haven't used the license since, sometimes I miss being around the airplanes though.....


Quote:
If you are set on bending the corners then you need to go with a 5000 series tubing. I use the T6061 and speed rail fitting that you can get at Aviation Industrial Supply in Denver. Just make sure that you get you coolers and boxes first so you can build the frame around them. A chop saw with a fine tooth wood blade work well to cut the tubing. Wear Eye Protection. Good Luck

Maybe I should change this to a "How should I build my frame?" thread.

I had read up on the speed rail fittings, and while they offer great flexibility it seems that they are just not as secure as a welded frame would be. That being said, obviously several companies sell them this way commercially, so they must hold up just fine, right?

My plan was to bend the perimeter out of tubing, run a couple longitudinal pieces for and aft and weld in the horizontals in place between these to support the cooler etc. Between the longitudinal supports and the perimeter, I was going to weld in some aluminum tread plate for a walkway.

Maybe I am getting locked in the idea of building the frame this way because I have the equipment rather than it being the best way. If you have the choice between a welded up frame, a speed rail frame, or any other type, what would it be?

Thanks again for all the replies!
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