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IndustryArena Forum > MetalWorking > MetalWork Discussion > Aluminum - steel rod materials question
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  1. #1
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    Aug 2010
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    Aluminum - steel rod materials question

    Hi,

    I have a materials question. I am designing a jig and it requires the use of rod, either aluminum or steel- anywhere from 1/4 inch to 3/8 inch dia.

    I had some initial prototype work done and found that 1/4 inch diameter, 8 inch long 6061 aluminum rod bends rather easily, which I do not want. I was wondering if I used either 1/4 inch or 3/8" diameter 7075 aluminum, would this be strong enough so that it would be very difficult to bend?

    I would like to keep the weight light however if I need to go to steel I can, wondered if Aluminum would be wrong choice for my application.

  2. #2
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    I'd try a piece of 3/8 7075. If it bends, then it won't work.

  3. #3
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    Would need to see a sketch of your jig with estimated forces.

  4. #4
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    .... Since txcncman wants to go all theoretical on you ( ),

    6061 T651 isn't the strongest al alloy/heat treat. 2024 T351 is almost 50% better tensile strength, while 7075 T651 is almost double.

    Have you considered 3/8" tubing?

  5. #5
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    Quote Originally Posted by fizzissist View Post
    ...

    Have you considered 3/8" tubing?
    I assume you mean steel tubing?

    For my application it might not work, I am thinking I need solid rod - there is a 1/8" bore in the 1/4 or 3/8 rod to hold another rod by locking set screw in the 1/4 or 3/8.

    I am thinking if the 7075 bends, I may as well go to tool steel beacause some of the cheaper steel alloys are only about 10 - 20 percent stronger than the 7075.

    i imagine tool steel raw material is much more expensive to both buy and machine.

    I figure if I go with 1/8" increased diameter and the 7075, the combined corss section area increase and tensile strength of the higher grade aluminum will increase strength 4 times. Just not sure how easy it is to bend.

    That brings me to another question, does anyone know where I can purchase either 1/4" or 3/8" 7068 rod - just a 1' long sample?

  6. #6
    Join Date
    Jun 2011
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    Have you thought about using an Epoxy in tubing?

  7. #7
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    Aug 2010
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    Yes actually I have, I was thinking though this would inrease the fabrication cost.

    Would this be a cheap process?

    Maybe I could buy such a rod off the shelf hmmm...

  8. #8
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    Jun 2011
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    Sure, try your local hobby shop for some construction materials.

    Do a test;
    Using the same size OD and bar length between two points, measure the bar's deflection with a known weight in the center.
    At this point, it doesn't matter the value, only the differences of each material/subject.
    I'd be willing to bet that a thin-walled steel tubing filled with an epoxy would yield better than any solid Aluminum and would definitely weigh less then solid steel.
    The only consideration I'd offer, would be to permanently seal the ends up somehow to entrap your new-cast inner. You wouldn't want it to fall out.

  9. #9
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    Jan 2006
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    In case you aren't aware, let me introduce you to the wonderful thing known as Mcmaster Carr

    McMaster-Carr

    Matt

  10. #10
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    Use carbon fiber. Doesn't bend easy, and it's super light.

  11. #11
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    Quote Originally Posted by underthetire View Post
    Use carbon fiber. Doesn't bend easy, and it's super light.
    Yeah I was thinking about that, isnt that stuff expensive?

  12. #12
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    Quote Originally Posted by nadsab View Post
    Yeah I was thinking about that, isnt that stuff expensive?
    $25 for a 3/8" x 12" rod.

    Matt

  13. #13
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    Does fiberglass rod lend itself well to laser engraving and machining?

    I was checking out isopthalic polyester resin and E-glass rod from MAX-GAIN SYSTEMS, INC.

  14. #14
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    You can put a mark on it but it doesn't cut very well because the glass fibers reflect the laser beam, with a CO2 laser anyway, I don't have experience with any others. You are mainly removing the epoxy, it gets real tough to cut once you hit the fibers. To cut thin sheets (0.015" or so) I use the same power I would use to cut 3/8" thick wood.

    Matt

  15. #15
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    Not too bad. Hobby shops like hobby king have all sorts of it.

  16. #16
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    My 3/8" tubing suggestion was in 7075... tubing because it'll be more rigid. How much? I dunno. I'm not going to spend my time doing the basic mechanical engineering calcs ..... You get to do that.

    It's Friday, and there's beer to drink.

    (btw, the formulas are on page 380 of the 11th edition of Machinery's Handbook. Probably on different pages of the book now, my copy is from 1941)

  17. #17
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    Quote Originally Posted by fizzissist View Post
    My 3/8" tubing suggestion was in 7075... tubing because it'll be more rigid....
    For the same material and same outside diameter solid is stiffer, more rigid, than tube.
    An open mind is a virtue...so long as all the common sense has not leaked out.

  18. #18
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    Quote Originally Posted by nadsab View Post
    That brings me to another question, does anyone know where I can purchase either 1/4" or 3/8" 7068 rod - just a 1' long sample?
    Order Aluminum 7075 Round in Small Quantities at OnlineMetals.com

    OR

    Speedy Metals - 7075

  19. #19
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    Quote Originally Posted by Geof View Post
    For the same material and same outside diameter solid is stiffer, more rigid, than tube.
    Tube is stiffer by weight only, Rod is stiffer by diameter, like you say.

    Matt

  20. #20
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    Weight was one of his criteria, with a max dia, hence my suggestion.

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