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  1. #41
    Senior Member Muskrat's Avatar
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    Quote Originally Posted by Kuhnsey View Post
    I came up with another design...thoughts on force exerted on pad eyes and lag eye bolts? And overall stability of the setup?

    Saw this design and its exactly what I need for hanging my WBBB on my screen porch. Went to the hardware store today, invested $35, came home with 2 chains (7' & 5', roof is sloped), 2 screw in hooks, 2 eye bolts, and 2 snap links. Drew up my design in AutoCAD, nothing too fancy, set my ridgline to be about 3.5' from the ground, drew in lines at a 30* angle to figure my height to set the eye bolts. Worked to be about 6' high. Total of 30 minutes in 97* heat and I now have a finished product. I have some pics taken on my phone but this computer is old and doesn't play well with others. I'll post some pics on Monday when I am at work to show my setup. Ridgeline is PERFECT

    Time to go sleep out on the porch with the ceiling fan on, looking like mid 60's here tonight.
    “He doesn't know the meaning of the word fear, but then again he doesn't know the meaning of most words”
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  2. #42
    Senior Member thekalimist's Avatar
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    Quote Originally Posted by Kuhnsey View Post
    I came up with another design...thoughts on force exerted on pad eyes and lag eye bolts? And overall stability of the setup?

    im using this technique in my room, but with 3/8" eye bolts (rated at 230#) in the ceiling [and wall] studs. surprisingly, the forces exerted arent that high.

    when i first installed the bolts, i attached a length of amsteel and put my weight (260#) into replicating the forces of hanging- this provided a fair amount of deflection on the eye bolt in the wall. you could see it in the hallway



    Going against the empirical evidence i had just gathered, i hung my hammock anyway. with my roommate watching the wall i plopped my heavy butt into the hammock - ZERO DEFLECTION. i even hopped around in it as best i could to cause failure without result. I attached carbiners to the ceiling bolts so that i can utilize me existing whoopie suspension.



    Ive slept in it the past three days and highly doubt ill return to my bed- dependent on the company...
    ...in it for pics.

  3. #43
    Senior Member XexorZ's Avatar
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    My physics is rusty, but I think this setup entirely removes the vertical force component from the wall-mounted eye (acting like a pulley in this system - translating that force vector to the ceiling) and keeps the horizontal force the same. In other words, its still trying to pull that eye out of the wall just as hard - its just not pulling down on it at the same time.

    Someone with a bigger brain and better memory correct me if I'm wrong =)

    (p.s. me thinks this should be much stronger - keeps lines of force in-line with the strongest axis of the eye-bolts... which is in line with them - but it is just as likely to pull a stud out of the wall - or break it - horizontally)
    Buy Tea at Jennifer's Tea Garden ( My Wife's Place )

  4. #44
    Senior Member thekalimist's Avatar
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    Quote Originally Posted by XexorZ View Post
    My physics is rusty, but I think this setup entirely removes the vertical force component from the wall-mounted eye (acting like a pulley in this system - translating that force vector to the ceiling) and keeps the horizontal force the same. In other words, its still trying to pull that eye out of the wall just as hard - its just not pulling down on it at the same time.

    Someone with a bigger brain and better memory correct me if I'm wrong =)

    (p.s. me thinks this should be much stronger - keeps lines of force in-line with the strongest axis of the eye-bolts... which is in line with them - but it is just as likely to pull a stud out of the wall - or break it - horizontally)
    i agree but, while im no scientist, i feel as though the 'dynamic load' is being divided between the four anchor points in the structure thereby spreading the force in the intended direction of the hardware
    ...in it for pics.

  5. #45
    Knotty's Avatar
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    Quote Originally Posted by XexorZ View Post
    My physics is rusty, but I think this setup entirely removes the vertical force component from the wall-mounted eye (acting like a pulley in this system - translating that force vector to the ceiling) and keeps the horizontal force the same. In other words, its still trying to pull that eye out of the wall just as hard - its just not pulling down on it at the same time.

    Someone with a bigger brain and better memory correct me if I'm wrong =)

    (p.s. me thinks this should be much stronger - keeps lines of force in-line with the strongest axis of the eye-bolts... which is in line with them - but it is just as likely to pull a stud out of the wall - or break it - horizontally)
    The pad eye in the ceiling is subject to whatever the tensile load on the suspension is. This load is carried in line with the pad eye's screws. So if the hammock is hung 30deg from horizontal and the hanger weights 200# then the suspension load equals the weight of the person in the hammock and each pad eye carries 200#.

    The eye screw in the wall is subject to a load vector that bisects the angle created in the suspension as it passes through the eye, so the load is actually angled upwards. With the same assumptions as above, the load would be 200# pulling up and out at a 30deg angle from horizontal.

    What's interesting is that if the hammock were simply attached to the wall, the load would still be 200# but on a 30deg downward angle. So maybe nothing's been gained here.

    Maybe someone can check my calculations.
    http://www.engineeringtoolbox.com/ve...ion-d_320.html
    Last edited by Knotty; 09-27-2010 at 19:39.
    Knotty
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  6. #46
    Senior Member XexorZ's Avatar
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    Quote Originally Posted by Knotty View Post
    The pad eye in the ceiling is subject to whatever the tensile load on the suspension is. This load is carried in line with the pad eye's screws. So if the hammock is hung 30deg from horizontal and the hanger weights 200# then the suspension load equals the weight of the person in the hammock and each pad eye carries 200#.

    The eye screw in the wall is subject to a load vector that bisects the angle created in the suspension as it passes through the eye, so the load is actually angled upwards. With the same assumptions as above, the load would be 200# pulling up and out at a 30deg angle from horizontal.

    What's interesting is that if the hammock were simply attached to the wall, the load would still be 200# but on a 30deg downward angle. So maybe nothing's been gained here.

    Maybe someone can check my calculations.
    http://www.engineeringtoolbox.com/ve...ion-d_320.html
    Ahhhh of course!

    makes perfect sense!

    I didn't "see" the force vector on the wall mounted eye - I thought it was 90* off the plane of the wall... which would have been a +... but that is clearly not the case!

    Thanks!

    Edit: Just realized a possible + on this type of system - if the wall eye fails the entire load is still suspended (at the wrong angle) from the ceiling eye. Assuming the now dynamic load pulse doesn't cause failure, this would prevent catastrophic failure... But good design would prevent this in the first place

    Edit #2: What if instead of using the wall eye as a pulley and passing the line through it, you attach it to the ceiling eye pre-loaded (under some tension to take out the slack)? Would this remove the vertical force vector from the wall eye leaving only the horizontal loading on that particular eye and only vertical loading on the ceiling eye? Assuming a very low stretch rope here of course...
    Buy Tea at Jennifer's Tea Garden ( My Wife's Place )

  7. #47
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    Not being able to balance a checkbook, I thought I needed some help understanding the load vectors descirbed here. The guy I sent this too has taught graduate level physics and has real world engineering experience. I sent him a link to this thread (starting on page 5) and got this response...

    This is an engineering problem. You don't want the hammock to fall, right?

    The weakest link I see is the eye bolts pulling out of the studs in the ceilings. The strongest way to rig this is to have the force pulling on the eye bolt perpendicular to the shaft of the bolt.

    The picture shown puts the majority of the force on the ceiling eye bolts parallel to the shaft, exactly what you don't want. It might hold if you have a big eye bolt screwed in really well, but the chances of pulling or wiggling out are maximized.

    You might as well just use two eyebolts, screw them into the wall and attach the hammock to those two points. If you really want to get fancy, then screw two eye bolts into the wall, one high and one low, and none into the ceiling. The bottom one acts like a pulley, and does apply a force vector that tends to pull the eye bolt out, but the top one has the force pulling directly down, perpendicular to the shaft which is what you want. Of course, you have to have strong steel eye bolts that can't shear.

    The odds that you will have a steel bolt shearing from a perpendicular force are much much less that pulling the bolt directly out of the wood studs with a parallel force. Think of a claw hammer pulling a nail out of some wood versus hitting the nail sideways and trying to break in in half.

    If you really want to keep is simple and strong, then why not screw the eye bolt into the wall at an angle, like the nail on a picture hanger? Ideally, the shaft of the bolt and the rope that hangs from it would be at a 90 degree angle.

    Boy, it sure makes sense to simply put the eye bolt in at an angle as opposed to going through all of this other stuff.... any other big brains out there who wish to refute or verify this?

    -jeff

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