Monday, June 6, 2011

TREE SWING

Retrotech is fun for me and folks similarly inclined, but this, I think, has a wider appeal: a tree swing!
A good, old-fashioned tree swing. The seat is red oak, assembled with carpenter's glue and wood screws (with predrilled holes: it's very hard even as oak goes!). Since it goes outdoors, I cheated on the finish, multiple coats of polyurethane.It has battens at each end and a lengthwise "rib," which makes it very sturdy. The 5/16" U-bolts (with fender washers and spring lockwashers) probably should be 3/8" or even 1/2" instead, but they'll do for now. They are the better grade, at least: check carefully and you'll discover some U-bolts are marked with a warning to not use them to support weight!

Most of the smoothing was done with planes and a scraper. It looks great but the seat is almost too smooth.

The knots are not as awful as they look; hidden in there are bowlines-on-a-bight at each side, with a series of clumsy hitches around them to take up the free end of each rope.

This project required a 25" 25-foot ladder (not 2' 1", much as I enjoy scale models I'm not one)* to reach the limb -- Jim the Tree Guy installed the ropes but I had to relocate my ham antenna: It ended up higher and farther away from the trunk of the tree, which is an improvement. The swing ropes clear the wire by a comfortable margin; the photo, shot from ground level, is a little misleading.
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* And a nod to Charles for catching my typo.

18 comments:

  1. Pretty cool!
    If you're going to replace the U-Bolts with something more substantial, look over at DX Engineering. They have a large selection of real stainless U-Bolts that won't get all rusty and yucky.
    http://www.dxengineering.com/

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  2. Hanging swings for kids is the primary purpose of trees, isn't it? We have a swing that's a single strand of rope run through a hole drilled through a short piece of 2x6. The kids really love it.

    What kind of rope did you use? Why a bowline on a bight instead of a plain bowline? Why not trim the rope instead of tying it up. It looks like you have plenty for height adjustment, even if you trimmed it.

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  3. So, when do we get pics of you and Tam trying it out? ;)

    Looks like a well-made and sturdy swing -- well done to all involved.

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  4. One bull hitch on those U bolts would do well.

    Or no high-tech U bolt at all: Plank hitch.

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  5. That's a one-blogger-at-a-time swing, Robert. Those 5/16" U-bolts, y'know.

    The rope is well-used climbing line, which the tree guy left (installed!) because they were too short for him. The ends are left long because I have yet to serve or whip 'em. Bowline-on-a-bight because it's the best knot I can tie with my eyes shut (climbing school) and also because it grabs tight but rarely jams.

    And U-bolts because I didn't want to bore a big hole in the oak and run a rope though it: tends to wick water in. But those are really too slender; I need tower-rated U-bolts with heavy galvanizing.

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  6. How's the front/back pitch? Generally you need a support triangle that starts higher up the rope and wider at the base to prevent tilt. Since you're a machine freak and you plan to replace the u-ies anyway, you could use 3/8 stainless rod with threaded ends and bent like a pyramid with about 10" verticals and a base nearly as wide as the seat.

    Prevents the seat from tipping front or back without consciously balancing, and makes it more stable for when you and TK have a "how high can you go" contest.

    It is otherwise a beautiful and timeless work of retroart you've got there. Thanks for sharing it...and cool new look for the blog, btw. :)

    AT

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  7. Sorry, I guess it ain't a new look, just a whole different blog. But old is better anyway...I deal in vintage jewelry and watches; the art and craftsmanship thrills me when I ponder what the process was like a century ago and compare it to the almost-exclusively assembly-line stampings and battery watch movements that populate retail jewelry showcases today. AT

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  8. Roberta,
    You never fail to make me smile.

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  9. A 25" ladder? For borrowers, maybe? :-)

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  10. Red right returning... Very nice, and I'll bet it gets some use!

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  11. @Roberta -- I mean the use of the picture() function iteratively and not the glob-form. I.e., pictures(@tam) and pictures(@RX).

    Looks like a fun swing -- I hope it makes the weekends in the backyard that much more enjoyable.

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  12. Read this, then take a look at how the weight is being supported on your swing seat.

    http://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse

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  13. Timmeehh: Fender. Washers. Also it's a clamped load, nuts/washers above and below the swing, unlike KC. Finally, the "beam" is made of two homogenous slabs of oak with the grain at 90 degrees, not a set of tack-welded C-channels.

    The Hyatt Walkway collapse is a famous example of bad installation on top of inadequate engineering.

    The weak spot in my swing is those 5/16 U-bolts, twice over: they are of marginal strength in and of themselves and the small diameter puts too much stress on the rope.

    The failure mode (if!) will be fracture of the U-bolt or the rope breaking long before the point of attachment between swing seat and U-bolt fails.

    If I can't find 'em anywhere else, I need to talk to Alexander Screw here in town; they can fab me up some nice 1/2" or 5/8" stainless versions, at a price barely below the point of pain.

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  14. Love the port and starboard designations by rope colors.

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  15. Thanks for taking the time to document your tree swing.

    I live in Texas and have a 20' branch that I would like to hang a 'swing seat'; similar to this post. I like your thought on using 'climbing line'; however, I want to make sure that I use the right rope. Given that I have never used 'climbing line', I'm ignorant of the appropriate rope to buy. As I research 'climbing line', I see (3) variables that impact this choice: rope diameter / static elongation / treatment.

    Hopefully you can offer some purchase URL's with the following criteria in mind:
    1. I am concerned with the rope rotting and breaking after 10-15 years
    2. I am concerned that the rope will wear at its connection to the tree; after hundreds upon hundreds of abrasive movements against the bark.

    Brad

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  16. Brad, I wish I could; the ropes I used were a gift from a tree-service professional. (Or "singing tree hippie," as the friend who rents my spare room calls him. Highly skilled by any name).

    One tip I can share: the way the rope is installed on the (stub) limb, there is no rope-on-bark movement. The end had been served back into an eye or loop and the other end looped through it. This snugs up tightly on the branch. You could do much the same with a good knot, but it will have to be untied and retied every year. The ropes are very long; the branch is about 20' up.

    10 years in the elements is a very long time to ask of any rope or line. I don't think I'd trust any that long. I actually bought a 25' extension ladder so I could work on my ham antennas; it is also long enough to reach the limb and assuming I still want a swing in five years, I'll ask my tree guy if he has any short bits of line left.

    As you note, "climbing line" is tricky stuff. This application doesn't call for anything superfancy; you are not worrying about what happens if the lead climber is being belayed from below and falls. But even the cheap stuff isn't all that cheap and it is a consumable.

    Any swing (or other "play structure") carries some risk. Even on a properly-installed swing in good shape, it is possible to injure oneself or others. I can't possibly take into account every concern for your specific situation -- that is up to you.

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