Bending aluminum

[Pete Harris]

I'm using a pair of aluminum alloy MTB flat bars as aero bars on my TT bike. They work pretty well,
but I'd like to give them a gentle upward bend toward the end.

Should I heat them, and how much, or cold bend them? Are they more likely to fail after being bent?
One thing that has to be to my advantage is that there is isn't much load on the portion in front of
the elbow pads.

I'm hoping some of you guys who know so much about materials might be able to help me out.

- Pete

 

[Jon]

Howdy Pete,

As a mechanical engineer I can tell you that bending Al is a bad idea. Your best bet will be to
find a pair of Al bars with the curve you want rather than risk almost certain failure by bending
them yourself.

While Al is a great material for some things it doesn't take kindly to any kind of bending. If I
remember correctly (materials classes were a while ago) both steel and Al fail at the same %
elongation [i.e. how much the material has been stretched or bent] except that steel won't fracture
for quite awhile after failure whereas Al fractures at or slightly past failure.

This means for your purposes that if you succeed in bending your bars the material has failed and
therefore the odds of it fracturing are very high. I don't know about you but I enjoy eating foods
that require chewing.

Jon

"Pete Harris" <[email protected]> wrote in message news:[email protected]...
> I'm using a pair of aluminum alloy MTB flat bars as aero bars on my TT bike. They work pretty
> well, but I'd like to give them a gentle upward bend toward the end.
>
> Should I heat them, and how much, or cold bend them? Are they more likely to fail after being
> bent? One thing that has to be to my advantage is that there is isn't much load on the portion in
> front of the elbow pads.
>
> I'm hoping some of you guys who know so much about materials might be able to help me out.
>
> - Pete

 

[Werehatrack]

On 28 Sep 2003 23:55:10 -0700, [email protected] (Pete Harris) may have said:

>I'm using a pair of aluminum alloy MTB flat bars as aero bars on my TT bike. They work pretty well,
>but I'd like to give them a gentle upward bend toward the end.
>
>Should I heat them, and how much, or cold bend them? Are they more likely to fail after being bent?
>One thing that has to be to my advantage is that there is isn't much load on the portion in front
>of the elbow pads.

If they aren't heat-treated, they might be malleable enough to bend, but if they're malleable enough
to bend, they will bend while you're riding. In other words, the bar that can be bent is not the bar
to ride with.

--
My email address is antispammed; pull WEEDS if replying via e-mail. Yes, I have a killfile. If I
don't respond to something, it's also possible that I'm busy.

 

[Bruni]

I make my own bars from raw 6061 T6 stock. I only use .049/1.2mm or greater wall and cold with an
outside mandrel bender. If you truly don't load this portion, only resting or guiding, you may get
away with this. Find a slip fitting tube (a few thousandths) to slip over the bar and generously
radius the inside edge. You then then place this tool at the start of the bend and tug until it
gives a degree or two. move outward 2-3mm and repeat. If the bar buckles, you must be willing to
replace it. Tom
--
Bruni Bicycles "Where art meets science" brunibicycles.com
410.426.3420 Pete Harris <[email protected]> wrote in message
news:[email protected]...
> I'm using a pair of aluminum alloy MTB flat bars as aero bars on my TT bike. They work pretty
> well, but I'd like to give them a gentle upward bend toward the end.
>
> Should I heat them, and how much, or cold bend them? Are they more likely to fail after being
> bent? One thing that has to be to my advantage is that there is isn't much load on the portion in
> front of the elbow pads.
>
> I'm hoping some of you guys who know so much about materials might be able to help me out.
>
> - Pete

 

[Jim Beam]

pete

technically, it's possible to do - afterall, drop bars are extensively worked, so if you have access
to the right forming tools and control processes, it's possible.

the practical reality however is different:

* you need mandrels to bend tube without buckling.

* bent bars generally start with thicker tube than straight bars to accomodate the thinning that
occurs in the material on the outer part of the curve.

* better quality bars are heat treated and anodized after they have been formed. some are even shot
peened. to work the material /after/ these processes have occured is not a good idea. at best
you'll end up with something that just looks ugly. at worst, you're going to seriously weaken the
material and compromise your safety.

so, your best bet, in my opinion, is to keep shopping around until you can find a bar that already
has a form closer to what you want, then cut or whatever from there.

i strongly recommend against working with your existing bars. heating them to soften prior to
bending would need to be a carefully controlled process. likewise, when you're done, you will need
to carefully re-treat to bring the material back into a hardened state. unless you have access to
the necessary process controls, the chances are that you're going to spend more time with your
dentist than you are riding.

if the "perfect" bar is still your goal, you may be able to find someone willing to make a custom
bar for you, but the cost for a one-off will be frightening. but, it may be less than your
dentist's bills!

jb

 

[Mike S.]

"Pete Harris" <[email protected]> wrote in message news:[email protected]...
> I'm using a pair of aluminum alloy MTB flat bars as aero bars on my TT bike. They work pretty
> well, but I'd like to give them a gentle upward bend toward the end.
>
> Should I heat them, and how much, or cold bend them? Are they more likely to fail after being
> bent? One thing that has to be to my advantage is that there is isn't much load on the portion in
> front of the elbow pads.
>
> I'm hoping some of you guys who know so much about materials might be able to help me out.
>
> - Pete

Why aren't you using a cowhorn? I'd say that they've gotten the bend down pretty well for TTing...

Mike

 

[Qui Si Parla Ca]

Bruni-<< I only use .049/1.2mm or greater wall and cold with an outside mandrel bender. >><BR><BR>

Wouldn't it be cheaper for the guy to just buy some cow-horms, Those mandrel benders are not cheap.

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302
(303)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene"

 

[Rick Onanian]

On 30 Sep 2003 13:10:29 GMT, [email protected] (Qui si parla Campagnolo) wrote:
>Wouldn't it be cheaper for the guy to just buy some cow-horms, Those mandrel benders are not cheap.

They can probably be rented very cheaply, or used at a proper metal shop.

Hey, I just thought of another option: local high school or vocational school. They will have the
equipment and will do it for free for you. Just avoid taking safety advice from the shop teacher
who's missing a finger.

--
Rick Onanian

 

[Pete Harris]

"Mike S." <mikeshaw2@coxDOTnet> wrote in message news:<I4%db.42179

> Why aren't you using a cowhorn? I'd say that they've gotten the bend down pretty well for TTing...

Since you asked ...

The reason I went to the MTB bars is their generous length, much longer than any of the cowhorns
I've seen for sale--and the price was right. They slip right into the clamps in my Profile carbon X
bars, which came with bike:

http://www.profile-design.com/carbonx.html

The elbow pads are clamped to the the MTB bars, in front of the main bar, not behind as in the
picture. I'm very low and stretched out, with not a lot of bend in the elbows. In fact, the way I'm
set up now, my hands are out in front of the wheel. Not UCI legal, by any means, but not quite
Superman either. Definitely uncomfortable, which is why I need the upward bend.

 

[John Everett]

On Mon, 29 Sep 2003 09:36:08 -0600, "Jon" <[email protected]> wrote:

>As a mechanical engineer I can tell you that bending Al is a bad idea. Your best bet will be to
>find a pair of Al bars with the curve you want rather than risk almost certain failure by bending
>them yourself.

As a mechanical engineer how do you think the "pair of Al bars with the curve you want" got the
curves in them? There are millions of us riding around with aluminum bars that have been bent into
their current shape. So why is bending aluminum bars (using the right tools of course) a bad idea?

jeverett3<AT>earthlink<DOT>net http://home.earthlink.net/~jeverett3

 

[Dianne_1234]

A pair of inexpensive MTB bar ends might have the right angle. Naturally, they bolt right on to the
MTB bar's ends.

[email protected] (Pete Harris) wrote in message news:<[email protected]>...
> I'm using a pair of aluminum alloy MTB flat bars as aero bars on my TT bike. They work pretty
> well, but I'd like to give them a gentle upward bend toward the end.
>
> Should I heat them, and how much, or cold bend them? Are they more likely to fail after being
> bent? One thing that has to be to my advantage is that there is isn't much load on the portion in
> front of the elbow pads.
>
> I'm hoping some of you guys who know so much about materials might be able to help me out.
>
> - Pete

 

[Jose Rizal]

dianne_1234:

> A pair of inexpensive MTB bar ends might have the right angle. Naturally, they bolt right on to
> the MTB bar's ends.

Yes, but these don't have quite the snob factor present with dropbars, which are used by all of the
hardest riding, longest travelling, most experienced cyclists in the universe.

 

[Chalo]

John Everett <[email protected]> wrote:

> "Jon" <[email protected]> wrote:
>
> >As a mechanical engineer I can tell you that bending Al is a bad idea.
>
> As a mechanical engineer how do you think the "pair of Al bars with the curve you want" got the
> curves in them? There are millions of us riding around with aluminum bars that have been bent into
> their current shape. So why is bending aluminum bars (using the right tools of course) a bad idea?

It's the state of the alloy. All handlebars are made from heat-treatable aluminum, and any necessary
forming is done in the annealed T0 condition, with additional annealing as necessary to allow the
desired degree of reshaping.

After forming they are solution heat treated and naturally or artificially aged to achieve their
working strength at the expense of further formability: For instance, 6061-T0 displays 25%
elongation before failure, but when heat-treated to T6 condition its elongation drops to 12%.

Chalo Colina

 

[Pete Harris]

[email protected] (dianne_1234) wrote

> A pair of inexpensive MTB bar ends might have the right angle. Naturally, they bolt right on to
> the MTB bar's ends.

That's exactly what I've done as an interim solution. In fact, the rig was basicaly unridable for
more than about 5 minutes until I put the bar ends on.

But my hands are still uncomfortably low, and went pretty numb during a 20mi TT last Saturday,
supporting some weight which really should have been on the elbow pads. I didn't mention this, but
the drop from the seat to the the bars is pretty extreme.

 

[Mike S.]

> > A pair of inexpensive MTB bar ends might have the right angle. Naturally, they bolt right on to
> > the MTB bar's ends.
>
> That's exactly what I've done as an interim solution. In fact, the rig was basicaly unridable for
> more than about 5 minutes until I put the bar ends on.
>
> But my hands are still uncomfortably low, and went pretty numb during a 20mi TT last Saturday,
> supporting some weight which really should have been on the elbow pads. I didn't mention this, but
> the drop from the seat to the the bars is pretty extreme.

Ummm, try raising the bars?? That'll help with some of the weight supporting issues...

Mike

 

[David L. Johnso]

On Thu, 02 Oct 2003 09:16:59 +0000, Mike S. wrote:

>> But my hands are still uncomfortably low, and went pretty numb during a 20mi TT last Saturday,
>> supporting some weight which really should have been on the elbow pads. I didn't mention this,
>> but the drop from the seat to the the bars is pretty extreme.
>
> Ummm, try raising the bars?? That'll help with some of the weight supporting issues...

Ah, yes, the "advantages" of threadless headsets. He can't raise the bars without getting a new
stem. Of course, until he tries it out, he can't know exactly how much rise he needs. And then he
has to buy another new stem.

--

David L. Johnson

__o | When you are up to your ass in alligators, it's hard to remember _`\(,_ | that your initial
objective was to drain the swamp. -- LBJ (_)/ (_) |

 

[Pete Harris]

"David L. Johnson" <[email protected]> wrote

> Ah, yes, the "advantages" of threadless headsets. He can't raise the bars without getting a new
> stem. Of course, until he tries it out, he can't know exactly how much rise he needs. And then he
> has to buy another new stem.

I hear you.

Actually, the Profile stem is integral with the base bar. I've still got a lot of steerer tube
showing on top, so I COULD raise the bars, but then I'd be slower. The idea is to be just
comfortable enough to go for 45-55 minutes without being distracted from how much your legs hurt.
Not quite the same parameters as a normal road bike fitting.

I think what I'll do is go buy another cheap MTB bar, heat it with a torch, and try to increase the
normal 15% bend with a conduit bender (all I've got). If it doesn't kink outright, I'll inspect in
for cracks, then have someone hold each end while I try some chin-ups. If it doesn't break, I'll
repeat this with another bar and put them on the bike.

- Pete

 

[Chalo]

"David L. Johnson" <[email protected]> wrote:

> Ah, yes, the "advantages" of threadless headsets. He can't raise the bars without getting a new
> stem. Of course, until he tries it out, he can't know exactly how much rise he needs. And then he
> has to buy another new stem.

And if he has a quill stem, he can raise it a whopping 3/4" to the "MAX HT" line and still not know
how much rise he needs.

--That is, if it wasn't jacked up all the way already, like most quill stem bikes in the
dealer's showroom.

Chalo Colina

 

[Rick Onanian]

On Thu, 02 Oct 2003 13:49:16 -0400, "David L. Johnson" <[email protected]> wrote:
>Ah, yes, the "advantages" of threadless headsets. He can't raise the bars without getting a new
>stem. Of course, until he tries it out, he can't know exactly how much rise he needs. And then he
>has to buy another new stem.

OTOH, once you own a few extra stems, it's trivial to mess with both height and reach with
threadless; with threaded, it's non-trivial to mess with reach, because you must remove the quill
each time.

When all is said and done, one isn't any easier or better than the other, save the specific
experiences of any individual (who should, in fact, go with what fits his needs better).
--
Rick "Has bikes with both" Onanian

 

[Dianne_1234]

[email protected] (Pete Harris) wrote in message news:<[email protected]>...
> I think what I'll do is go buy another cheap MTB bar, heat it with a torch, and try to increase
> the normal 15% bend with a conduit bender (all I've got). If it doesn't kink outright, I'll
> inspect in for cracks, then have someone hold each end while I try some chin-ups. If it doesn't
> break, I'll repeat this with another bar and put them on the bike.
>
> - Pete

Or just get some 7/8" diameter 6061-T6 and use your conduit bender on them "as is". Choose wall
thickness about 0.063 or more. I've done this for aero bars, and except for the larger radius in the
bend, and the aluminum oxide getting on my hands, it works great.