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  1. #1
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    Apr 2008
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    Question Black Pipe Fittings / Strength

    Howdy, All:

    I am building a back yard horizontal bar (think one gymnastics bar) for my daughter to break her neck on. I'm wondering about the strength of my design and thought I'd ask for your input.

    My design: I will cement two ten foot 4"x6" PT posts in the ground 4 feet deep (I live in Maine and this is a good frost depth). I will then secure an 8 foot section of 1 1/2inch black pipe (think steel pipe) to these posts by attaching a flange to each threaded end of the pipe. The flange has four holes for screws. Instead of using screws, I will drill through the 4"x6" and use carraige bolts to through-bolt the flange/pipe to the posts at either end of the pipe.

    My concerns: The flange only seems to thread onto the black pipe about 1/2 way through the flange (approximately 1/4" - 3/8" into the fitting). Is this enough to hold over the long haul? No matter how much tension I put on the fitting to get it to screw on further, it will not budge. Also, the four holes in the flange that I will attach by through-bolting into the 4"x6" posts will only accept a carraige bolt that is 5/16". I've chosen galvanized carraige bolts in this diameter. Will four at either end have sufficient shear strenght to keep the pipe from breaking free?

    Thanks much for any insight or additional ideas you can offer -- either about the design or the strength of the attachments.

    Tim

  2. #2
    Join Date
    Aug 2007
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    Default Re: Black Pipe Fittings / Strength

    Why not bore a hole through the top of the post, run the pipe through, then install the flanges? The post will support the pipe and the flange will keep the pipe from turning.

    In answer to your question about the 5/16" bolts, yes, 8 of those will be more than enough to hold several hundred pounds. Just how big is your daughter anyway?

    The only "flaw" I see in your plan is the possibility of the pipe becoming loose in the flanges. To prevent that I'd either go with my suggestion of putting the pipe through the post OR have the flanges tack welded. If you're going to the efforts of having them take welded, then I'd forget the threaded flanges altogether and have the welder install a 1/4" plate on the ends of the pipe. Holes of any desired size would be drilled through the flanges to attache to the posts.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  3. #3
    Join Date
    Apr 2008
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    74

    Default Re: Black Pipe Fittings / Strength

    A Spruce -- thanks for the quick response.

    I had thought about going through the posts with the pipe, then putting the flange on the outside to hold all secure, but unfortunately the only flange they sell threads onto the pipe so that the flat surface is facing outwards (i.e. it will only attach to the inside of the post once screwed onto the pipe).

    My daughter is 10 years old and has been a gymnast for the last 6 or 7 years -- quite powerful for a little girl, but nowhere near "several hundred pounds". Probably closer to 70 pounds of muscle! I'm expecting she'll be able to whoop me soon.

    I had thought about getting the flanges tack welded onto the pipe. . . just didn't know if it was necessary. I think while the concrete is drying I will do just that. Makes perfect sense and will keep me from worrying about it coming loose. I can also go with your plate steel idea -- good one.

    I knew I'd get what I needed here! Thanks for your input.

    Tim

  4. #4
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    Default Re: Black Pipe Fittings / Strength

    Quote Originally Posted by TRLambert View Post
    My daughter is 10 years old and has been a gymnast for the last 6 or 7 years -- quite powerful for a little girl, but nowhere near "several hundred pounds".
    Whew! You had me worried there for a moment.

    Quote Originally Posted by TRLambert View Post
    I knew I'd get what I needed here! Thanks for your input.

    Tim
    You're welcome.

    The nice thing about using flanges, welded or otherwise is that you can adjust the height of the bar as necessary.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  5. #5
    Join Date
    Apr 2008
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    Default Re: Black Pipe Fittings / Strength

    The nice thing about using flanges, welded or otherwise is that you can adjust the height of the bar as necessary.

    That's what I was thinking. I could pre-drill holes to allow for movement up / down on the posts as desired. Of course, I'd do the drilling once the posts are in the ground, as I'm not confident I can get them exactly the same depth so the bar would hang level.

    Thanks again.

    Tim

  6. #6
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    Default Re: Black Pipe Fittings / Strength

    Another thought that just came to me is if you have flanges welded on the pipe, to have the pipe protrude through the flange an inch or two. This would still put the bearing of the pipe on the post, the bolt would merely keep the pipe from spinning.

    Just a thought ... Maybe I need more coffee before I offer any more advice?
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  7. #7
    Join Date
    Apr 2008
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    Default Re: Black Pipe Fittings / Strength

    That's great advice. . . but the piple won't fit through the flanges -- would have to use the plate steel idea and have the welder fabricate it that way.

    If I do go this route, how would one go about drilling nice, clean holes into the post? They would need to be probably 2 inches or larger in diameter so the pipe could be wiggled into place once the posts are set -- there wouldn't be much flex in the post, since it's 4"x6" and 4 feet in the ground. In other words, the hole would have to be larger than the pipe so I could slip it in at an angle to get it to set prior to bolting.

    Would my dewalt 18v cordless have enough a$$ to drill such an aggressive hole? I'm not sure the old girl has it left in her!

    Tim

  8. #8
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    Default Re: Black Pipe Fittings / Strength

    Yes, to put the pipe through the flang you'd have to have the flanges fabricated.

    There are two styles of bit that will drill an absolutely clean hole and that is an auger bit and a Forstner bit. The auger may be hard to come by in that size, the Forstner will be easy, but relatively expensive. You could also accomplish such a task with a spade bit without too much tear-out on the surface, though the drill really won't like you much! LOL The only other bit that comes to mind that would do the job well is a hole saw. You'd drill the hole to the depth of the bit then snap out the core. The hole saw will probably be the cheapest set-up, even if you have to purchase the mandrel with it, assuming you don't own one already.

    As for installing the pipe between fixed posts, you'd only need about an inch of flex to fit the pipe (assuming a 1" nub protrudes past the flange ). That's only a 1/2" that each post has to flex which shouldn't be that big a deal. If necessary use a jack to assist, but have extra hands handy to hold/work the jack and install the pipe.

    A wise man would have only set one post and installed the pipe before setting the second post.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  9. #9
    Join Date
    Apr 2008
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    74

    Default Re: Black Pipe Fittings / Strength

    I do have a hole saw and will have to give that a try -- I hadn't even thought of trying to use it!

    Wise man say: Setting one post, installing the pipe, then setting the second post will not allow for one to change the height of the pipe/bar once the second post is fixed in place with a hundred pounds + of concrete.

    Wise man also say: When one man has to hold heavy 8 foot pipe six feet in air, try to position 10 foot 4"x6" in ground, mix concrete and put in hole, and stabalize by ones self, man is likely to get knocked on the head pretty hard! Unfortunately there is not much help in my neck of the woods. . . .most things I do require one-man ingenuity!

    Go back and get some more coffee, grasshopper!

    Tim

  10. #10
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    Default Re: Black Pipe Fittings / Strength

    A wise man would have used telescoping posts ...

    You're gonna make this difficult, aren't you ...

    Because you want to have adjustable height, I think I'd just go with flush fit flanges on the pipe and bolting it in place. I think that I'd also make the flanges 8" long so that two attachment holes could be drilled on 6" centers and just use 3/8" or 1/2" bolts (two per side) to attach to the posts. When it comes time to raise the pipe, all you do is remove the bottom bolt and rotate the pipe upward, drill a new hole and you're done. No having to man-handle a heavy pipe or splay out posts or any other such nonsense.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

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