aluminum tube bending

[BWD]

Hi. First post on subforum.
I am making a sailing outrigger detailed at
Outrigger canoe plan....
I want to use Aluminum tube for crossbeams.
With beamboy software I have figured 3 inch OD x 0.125 6061 al tube will do.
I have had some ideas on welding it up into an L bracket shape, but am thinking these ideas depend too much on too much perfect welding.
I am thinking now it might be better to bend the tubes, as shown in the sketch below.
My questions for anyone who cares to answer:

1.how hard would it be to get that bend (about 30 inch radius) in 3 inch x 0.125 tube? I assume pretty easy for a normal fabricator that does bending...

2. would it need to use 6063 instead of 6061?

3. If 6063 would it need to be treated to give it the shear and fatigue properties to match 6061, or could I just make sure I don't sail it hard until it has gotten a little age on it (ie next June)?

4. Finally would extrados stretching or some other consideration "over my head" require a thicker tube?

Sorry a lot of questions but I put them up because actually they seem commonplace enough to get an easy answer from anyone with experience.

Thanks in advance!

[lazeyjack]

you could form that is 2 inch, but not 3, it would dent,
You could make the pattern and take it to a shop that does exhaust tubing
the bend is so gradual, you won;t loose wall thickness
You are lucky to be able to get 6061 t6 off the shelf

[BWD]

Thanks for your reply, I am not going to bend it myself.
I found a marine fabricator who makes tuna towers, radar arches and similar things. Looking at their work I think they can do it easily.

An employee there said they have the machines to bend 2.5 inch sched 40 6061, 6063 Al pipe or 3 inch x 0.125 wall 6061, 6063 tubes. The boss is out of town, I will see what he says about it next week.

I think either alloy will take the large radius bend(?). Thanks for reassuring me about the thinning. Hopefully with little thinning, shear strength also will be pretty good still?

Maybe I will end up at an exhaust shop if the marine guys won't bother with me. It is pretty similar to a big truck exhaust after all....

Just looking for a ballpark answer, for example would it decrease strength 10% (ok) or 50% (not ok).

[lazeyjack]

look I am not a mech eng but from my exp. which is long( unfortunately) I can see no weakening at all, of coarse just by forming it into that shape you are building in strength
you compare it with the beam across the hulls of a 15m cat, often they use a tube of bit of boom section, 4mm wall, then they weld a bracket for the forestay ACROSS THE Beam, which is an engineering NO!! and not only does this make a breaking point, it also destoys the tensile around the weld area
you dont have any of this, go for it looks good

[BWD]

Thanks again, then!

[murdomack]

As an old piping man, nearly as old as Lazeyjack, , I would recommend that you stay with the marine fabricator rather than the exhaust bender. You have seen examples of his work and his equipment.
The exhaust bends that I see are not of the same quality as what one would expect from a true pipe bender and could be described as "fit for purpose". You want something that will be uniform, strong and pleasing to the critical eye.

[kmorin]

BWD,

I've bent many lengths of aluminum pipe, 4" and smaller, a little aluminum tube, and would suggest this very small deflection you've shown will be easily done by segment bending. This device (a single shot bender) is simply a shoe or half pipe die pushed against the side for 1-4 degree bend/kink/deflection.

Adding these 'step bends' together will make a nice smooth curve that results in the shape you've shown, especially since you only want 30-40 degrees of change.

If you were single shot bending a 90 then 6063 is more sucessful as its less rigid, more malleable and will harden into 6061 overtime- anyway.

Both 6063 and 6061 will increase their tensile strength as they work harden in the bending or rolling processes. I believe that figure is nearly 30% gain for both materials in the area of the cold deformation? but I can't cite a source for this figure.

The alternative way to create this bend is to roll the tube/pipe in an angle rolls with this size pipe/tube dies. This would create an absolutely clean shape and would strain harden either alloy, but would be much less likely a tool used by tower builders who would find more use in a hydraulic one shot style bender, but they probably have both tools.

There will be no meaningful side wall thinning in this size of tube at the radius you'd shown.

Tube dies of this size would be hundreds of times more rare than pipe dies of this size. 3" schedule 40 6061 pipe is 3-3/8" OD and would be the most common die for most equipment as the Greenlee company makes conduit/pipe benders with this size shoe/die/bending tooling. The next pipe size down 2-1/2" is only 2-7/8" OD so tubing dies are required for tube dimensional extrusions.

I agree that a truck exhaust shop will be (more) likely to have a 3" tube bending capability. Either single shot with a full 90 deg die or with shoes that will allow segment bends resulting in the radius you want.

Cheers,

[bntii]

If you need a shop I have used these guys in the past:

http://www.mandrelbendingsolutions.c...let/StoreFront

Paul is a great guy and his shop is just over in Severna Park if you are in northern VA it's not too far.
He will not have aluminum tube so you will have to supply but his shop is filled with high end mandrel bending rigs and he can handle tube up to 4".

[BWD]

Thanks! It's amazing how many calls I have made without finding someone that can do this.
If your suggestion doesn't work I may have to call one of the shipyards in Hampton Roads. I think they could bend a submarine around an aircraft carrier down there, but I am not so sure they'd bother talking to a little guy, unless I can make some contacts....

[kmorin]

BWD,

call the local electrical contractors who bend industrial size conduit, not house wiring people, they don't usually work this heavy but anyone with a Greenlee 777 or 880 with big shoes can do the work. The people with these tools install large diameter pipe in construction and heavy industry so make sure you're not calling someone who isn't in that 'bidness'.

Cheers,
kmorin

[glensail]

Hey...My first post! Seriously I'm working on a steel hull, alum deck 46 footer. I've an idea to make simple, cheap, but reliable hatch seals. Can alum pipe of 3/4 or 1 inch be bent in a circle of 20 in Dia? Here's my idea....

[lazeyjack]

yes 10 inch r is not tight at all, you could use solid to make it tighter, I can not quite figure your machine, looks interesting
you can buy hand tube benders for one inch I think the r on mine was about 4-5 inches, needed a bar on the handle but did all hand rails with it years ago

[BHOFM]

My expertize is in aircraft design and bending or working
of any metal will harden it! Sometimes this can cause a
problem as the material next to the bend is softer!

To retain the working strength of the material you need to
heat the entire piece after bending and let it cool slowly!

With aluminum, just heating to 350f will do the trick!

You may also want to fill the pipe with fine sand prior to
bending to help retain the shape!

[lazeyjack]

no you do not need to heat or anneal,and what you have said BHOFM , will most certainly put this guy wrong. please post from EXPERIENCE bECAUSE JUST GUESSING REALLY BUGGERS PEOPLE UP I have done bends up to 2 inch in an ordinary pipe bender, it that case I did anneal, but one inch no, use 1/8th wall And when gauging temp of anneal, who the heck can tell 350, the drill is you light your oxy acetylene up, turm OFF the oxy, blacken the area with the acetylene andthen fire on the oxy, and heat the tube til the black goes, then quench
here is a sketch,
on ss tube the slipper and former are critical, must fit snug, slipper need be about 400mm long, bore block in lathe and saw off the other half(alloy slipper)
mt the whole thing on a post on floor, a must when doing your own handrails in ss, or alloy

[BHOFM]

When bending lite tubing, I use a heat gun to heat
the work!

Who ever bends the tubing for him should be aware of
the properties of metal and advise him as the steps
he need to take to ensure the structural strength of
his material!

My post was a generalization of working with metal, not
a detailed set of instructions!