Expanding center section of a tube
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  1. #1
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    Default Expanding center section of a tube

    Any good ideas on how to do the central bulge on this in an economically efficient way (I'm looking to produce only a few of these, so $1000s in new tooling isn't in the cards).
    handlebar.jpg

    The material will be cromoly steel, seamless, wall thickness of about 0.035 in., thicker if I need to go that way to get the radius bends without kinking on my JD2. Starting diameter is 1 in., expanded section is 1.25 in. May also try some aluminum, thicker walls.

    Appreciate advice,

    jb

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    Use a formed sleeve. For only a few, and at minimal cost, you're chasing an errant errand to try to bulge the center.

    Ditto for Al, but worse due to the crap fatigue properties of aluminum. You're making bicycle handlebars, do you REALLY want a plaintiff's lawyer asking you during a deposition why you half-assed a critical safety component?

    People have literally died from sudden handlebar failure.

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    A job for hydro forming? Is tube seamless?

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    Here is a video of how it’s done commercially. Duplicating this process cheaply and at low volume looks daunting.



    denis

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    Having watched the automobile tailpipe expanders work, is there any reason you couldn't put something like that on the end of a smaller tube and use an extended mandrel draw bar? You could probably make that yourself.

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    use A513 1020 DOM tubing. 72,000 psi yield.

    you will have to expand it first... make an extremely stout die and hydraulically expand the tube while it is constrained inside.

    yield pressure calculator:
    Barlow's Formula - Internal, Allowable and Bursting Pressure
    yield pressure = 2 x 72,000psi x .035" wall / 1"OD = 5040psi

    For your tube specs a porta-power pump would do. It would get you to 10kpsi... probably enough to coin it decently?

    industriall tube expanders run very high pressures, like up to 50,000psi. your wall thickness and how well you wnt to coin the tube to your die will effect the pressure needed. reference:

    Hydro Expansion Unit

    A nice machined sleeve would be much easier. You could also plug weld the sleeve. put a hole or two in it crosswise, which will be covered by the stem clamp and plug weld the hole or braze it. When installed the plug weld is completely invisible.


    good luck with the jd2.

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    Have you considered bulging it first, then bending it ?

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    you want to make a few of something that's been mass produced by the millions for over a century?

    Hydroforming

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    Hmmm...Simple split die of MS with (4) bolts holding together, accurately placed black powder "blob"....BackYard, cover with dirt, 3' long fuse.

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    I think the formed sleeve is the way to go. Taper it on the lathe, slide it on, braze it with brass or silver.

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    Yup. I build custom bicycle frames. You can go to Walmart and get one of the millions produced in China, or you can have one built to ride the way you ride. Why make a burger at home when you can get one of millions produced at MacDonald's?

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    That was the plan. But if I use the sleeve method, I'll add that last, since it won't interfere with the bending dies.

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    The Boston Police Dept. might have something to say to me afterwards...
    ;-)

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    Quote Originally Posted by jepbjr View Post
    The Boston Police Dept. might have something to say to me afterwards...
    ;-)
    Doo your work on july 4, p.m., no one will care....

    Out here in "flyover land" we hear gunfire all the time.....

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    Good info and good advice. Thanks.

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    Cool, thanks Denis.

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    Economical approach: go to WalMart, buy as many bicycles as you need parts, remove handlebars, throw the remainder of the bikes away.

    Done!



    On edit: I see that you already anticipated my WalMart advice before I wrote my reply. Oh well ... that's what I get for trying to be cute!

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    That's why most all made in USA metal bars have had external shims with the exception of Easton.

    Maybe try and source pre bulged bar stock that hasn't been bent yet? Would likely take customizing mandrels to bend around the bulge.

    If it's really low volume 'bespoke' stuff, I would just silver braze on a shim and powder coat or plate over it after blending in the edges. I wouldn't do it, but if I guy just had to...

    Or just go one piece bar/stem...

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    Quote Originally Posted by jepbjr View Post
    Yup. I build custom bicycle frames. You can go to Walmart and get one of the millions produced in China, or you can have one built to ride the way you ride. Why make a burger at home when you can get one of millions produced at MacDonald's?
    Well, seems like you have all the answers then.

    I don't suppose it's occurred to you that what you want to accomplish, is beyond the capabilities of a shitty hardware store bender?

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    Are you actually trying to make your own bars? Or form tubing for frame components? Relatively small manufacturers like Knolly bikes have aluminum frames with hydroformed parts, made in Taiwan though. I have not heard of anyone making modern handlebars on a cottage industry basis. Back in the early 90's, Syncros made so called flat bars out of straight aluminum and titanium tubing that was lightly bent to sweep back, but the connection to the stem was done with a two piece adapter taking the .875" handle bar to 1.125 or whatever the numbers were at the time. These were longer than the stem's clamp tube and chamfered at the ends, all to prevent stress risers between stem and bars. Stress management near the stem is the key issue. Ask me how I know....


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