Improve My Tree Swing

The tree swing debate rages on...

But, this is great info.  I have done nothing yet, maybe this weekend.  The straps shown are cheap enough that they may be the answer.  However, I also want to try my hand at rigging up my own.  We'll see.  

jharry3 said:

In reply to SVreX :

Ok.    A Square 4 x 4 has a section modulus of 10.67 in^3 vs 4" round of 6.28 in^3.   (Assuming the same material)   A square 4 x 4 has more cross sectional area than a 4" round so more strength in shear as well.

But a 12" circumference, as stated,  is only 3.81" in diameter so the number is 5.43 in^3, half as strong in bending  as similar material 4 x 4. 

My error on the 10 x safety factor - I work on offshore oil projects and its 10 x for us.  OSHA is less.

Tree branches crack from lots of reasons like insect infestation, disease, just plain bad luck.  

 Cured wood that is protected from moisture will last a hundreds of years or more. We still have colonial era buildings in America.

We can get really pedantic and start comparing round oak to square pine and prove oak is stronger even with less section modulus because of its inherent strength but I am comparing apples to apples.  

Lag screws, unless stainless, corrode eventually and the threads shear off.  The corrosion also causes local deterioration of the wood in which its embedded.  Sure, there are thousands of swings supported by lag screws, but, like I said, I am a structural engineer and tend to overdo it sometimes.      My kid's swing didn't fall and the one in the picture did.

Gotcha.  Thanks  

But it I have to disagree with you on the “cured wood will last hundreds of years” comment.  The only wood we have that has been around hundreds of years is old growth timber. We essentially don’t have any anymore. Timber is now fast growth, and the annular rings are much further apart. It’s much weaker, and more prone to insect infestation. 

Pressure treated wood (like your 4x4’s) are not cured. They are injected with moisture that expands the cellular structure. 

And any outdoor play set is definitely not protected from moisture, regardless of what kind of wood it is. 

I agree about not liking lag screws in a branch that size. That’s why I suggested the straps. 

In reply to John Welsh :

I see no reason why you can’t rig your own. 

Just be careful with that smaller rope. It can cut into the bark of the tree, or the tree will grow through it and around it if it can’t expand as the tree grows. 

So, my thoughts as an amateur arborist and a darn fine rigger.

Anything you can do to reduce the amount of contact with the tree is great, but I understand the conundrum.  Your link failed because it was A) fully responsible for all of the weight, B) was multiplied by the spreading force of the round branch, and C) was a frictional bearing point.  Proper rigging dictates at least one wrap of the chain so the full circumference shares the load and spreads the weight more evenly over the links.  The problem with that is the choking effect of the links on the branch.  It won't take long until the chain is buried in the cambium.

My suggestion is to ditch the chain.  Get a couple lengths of 3/16" stainless aircraft cable.  3/16" is overkill and will easily support 20 times the weight that the branch could.  Grab a couple lengths of a smaller ID/larger OD hydraulic hose from your local hydraulic hose fab joint.  They'll likely have a dumpster full of it.  Make a couple things like this:

This depicts a (maybe) 18" long section of cable, with thimbles and swages at the ends, passed through a section of hydraulic hose.  I use hydraulic hose for two reasons.  First, its highly resistant to abrasion - second, it's highly resistant to UV.

Wrap those around the branch, bring them down and use a 5/16" forged shackle to join the loops and your drop rope.  The hose will minimize damage to the tree and it will allow for greater circumference as the branch grows.

Do use stainless aircraft cable.  Don't use vinyl or plastic coated cable.  Not only will plastic coating just degrade in a few years, you will be clamping to a vinyl sheath instead of properly clamping to the substrate
Do use something for your drop ropes that will last.  Don't use sisal or hemp rope, it will rot.  Even sailors with their fancy UV-protected poly or nylon rope replace theirs every couple years because they are just UV resistant, not UV-proof.  I don't suggest aircraft cable since it is hard to protect the ends from pokey things.  Chain is good.
Do use rope thimbles at every joint that uses cable or rope.  Much like wrapping a chain at least once, the thimble spreads the load and provides protection for the rope.  Just hanging a rope causes it to kink and pinch and be the friction/fulcrum point.

The threaded "quick links" like you pictured are not rated for any weight.  I'm sure they're safe for your application, but the proper hardware is a forged u-shaped shackle like this:

While stainless typically doesn't have quite the weight rating of steel, a 5/16" shackle is still rated in the thousands of pounds and will last forever.  Don't use S-hooks.  All of your joints need to have a positive, closed, continuous loop to have an actual weight rating for suspension, so a standard screw eye with a bent loop isn't nearly as strong as a forged eye.  It's overkill in your application, but I'm just giving you the "right" way to do it as if you were building a commercial/public swingset.  Do what you wish, but if you follow the above guidelines, the swing and its rigging will outlast the tree, your children, your grandchildren, and most diamonds.

Curtis ftw.

John, if you want, I have some 3/16" galvanized aircraft and possibly some thimbles/swages.  I could make the cable part for you but I don't have any hydraulic hose.  You would have to select hose that was big enough to pass the cable loop through.  If you want, PM me an address and I'll fab up some and throw in a couple shackles, (steel, not stainless).

That will just leave you to hang the swing without having to source the other stuff.

Hey Curtis,

What's your source for the aircraft cable?  That's exactly what I had in mind when I said wire-rope on the last page, but I'm not sure where to get the aircraft rated stuff.  I know they sell some wire rope @ the home good stores, but I don't know if that's the same, but that's exactly what I intended on the last page. 

I'm a theater Tech Director, so I rarely use 3/16", usually 1/8".  Visually speaking, it is better for me to use a greater number of 1/8" pick points than fewer 3/16" lines.  But for buying both, I use Amazon.  Sometimes I use StageLightingStore.com, RoseBrand, or BMI, but that's only if I can't find the black-dyed cable I need for theater rigging.  As long as you don't need the black stuff like me, Amazon has what you need for cheap.

Expect 50-60 cents per foot for 7x19 stainless if you get quantities of 100' or more.

The term "aircraft cable" has somewhat become interchangeable with wire rope.  True aircraft cable needs to be rated for aircraft use, but for this type of overhead rigging, I always go with 7x19 strand for the right combo of flexible and strong.  Stainless is rated a little lower than galvanized, but with a 2000 lb break load, I can easily load 1/8" stainless to 200 lbs per pick point and sleep well about it.

I think if you bought actual "aircraft rated" wire rope you'll pay a pretty penny for what probably amounts to the same spool of stuff, just submitted to very rigorous testing.  True Aircraft cable I believe is 7x19 strand.  If you want less flexible, go with a 7x7.  If you want cheap, stiff, and pretty strong, get a 1x19 twist.

chandler said:

Curtis ftw.

SOOO true!  

I will send a PM to Curtis!

I can get you any hydraulic hose scraps you need if you don't find a source closer. 

In reply to EvanB :

Curtis says I'll need about 12" each of 1" ID hose.

Would you mind just dropping some in the mail?  I'll gladly cover shipping. 

PM sent. 

SVreX said:

Me too!

dculberson said:

I swear you guys help me out more than my family sometimes.  Glad we could help.

Hoes acquired. 

Swaged cables and shackles went out today.

Can I swing in it if I come to Ohio?

So cool from both of you! 

Also, good to know that the swing might survive in the unfortunate event the tree ever gets hit by lightning and catches fire. 

Curtis, 

I envision some awkward photo of me pushing you as you swing in my front yard. 

Or, was this some lightly veiled sexual advancement towards my wife? 

John Welsh said:

So cool from both of you! 

Also, good to know that the swing might survive in the unfortunate event the tree ever gets hit by lightning and catches fire. 

 

Curtis, 

I envision some awkward photo of me pushing you as you swing in my front yard. 

Or, was this some lightly veiled sexual advancement towards my wife? 

Haaaa.  

Now we have to do the awkward photo of you pushing me in the swing.

P.S... send pictures of your wife  (kidding)

In reply to EvanB :

You's hoes arrived

Forgot to mention, careful around the ends. The saw I used cuts fairly clean but there can still be some random wires sticking out that will poke you. 

Did you get the cables yet?

In reply to Curtis :

Cables arrived. Awesome!  Busy weekend and nothing further has happened yet. More later. 

Hmm, this thread bubbled to the top (I'm guessing canoe)

Do we have a picture of the completed and installed product?

So, here is the almost 1.5yr old update.  Curtis' cables arrived about March 25th.  Evan hoes had gotten here a couple of days earlier.  

The hoes are super ridged.  That can not really be bent to conform to the bend of the tree but even greater issues is that the eyelets on Cutis' cables were too big to pass through Evan hoes.  Net result, the hoes were never usable for this application.  So, then I improvised.  

I had some old garden hose here.  Simple, cheap grade stuff.  I slit the hose long ways, laid the cables in the hose and then sealed it all up with gorilla tape being mindful to keep the split on the hose upward so the the closed side of the hose makes contact with the tree.  

The cables and shackles that Curtis sent me are awesome, great quality stuff.  To keep the bolt in the shackle I just ran a black zip-tie through to act as a safety so the bolt can not back out.  

The swing still see lots of use, this photo taken last month with now bigger, near 50lb kids.  

Speaking of kids getting bigger, I have added a rope swing with a round seat too. 

At my daughters request, I also added another rope connected to a pink, play, baby seat.  This is so she can put dolls in the seat and swing them.