Improve My Tree Swing

Three and a half years ago I put up a tree swing in my front yard.  This pic is from the day it went up in June '15.  At the time my little girl was almost 1 yr old.  

I used a simple hardware store chain.  At the top, on the tree branch, I used 7 links plus 1 closure link like this.  Therefore, 8 links total or 11 inches around the branch.  

From there I just hung down two sections of the same chain.  The pivot point at the top branch is then just "chain to chain".  This has worked well enough for 3.5 yrs and with a lightweight kid but I always knew it would be temp solution.  Now, you can see where the chain wrapped around the upper branch is growing into the tree.  Furthermore, we had a friend over last week.  My 4.5yr old now weighs near 40 lbs.  This other girl was heavier.  Sure enough, on the other girls turn, one chain broke.  Everyone was fine.  The perception was even that it was fun...lucky!  

This pic from just moments before the break:

The break happened at the top, at the link that would have been the pivot.  

So, whats the better or more permanent solution?  

If not one, should I just do the same with a bigger chain?  But, the chain makes for a poor pivot point.  Better?  

My real questions are: 

• How to best attach to the tree?
  • Branch is only 12" diameter
• How to best pivot from the chosen attachment?

I'd like this to be a two chain/rope swing not a single attachment point like you might have with a tire swing.  

I replaced chain with 1/2" steel cable at my friends house when I was swinging with my newborn and wound up on the ground. It's held up fine the last 4 years, but might be overkill.

If you have a conventional swing set they make brackets with brass/bronze bushings in them that take up the movement. Even with that you still get some link wear, just not as much. With a branch your best bet is to use rope (or cable I guess, I've never seen that) and replace as necessary. 

They sell nylon web strapping for this purpose. First example I found:

https://www.amazon.com/SWING-HANGING-capacity-auto-lock-carabiner/dp/B01GFD3K6Q

That look to be just one strap and caribiner. we've got something similar that’s served us well for several years and doesn’t seem to be cutting into the tree or itself at all. 

These are porch swing hooks:

They have a nylon pivot bearing. You can buy them easily in Lowes or HD. 

A 12” diameter branch is reasonably hefty. I don’t see why you couldn’t screw them straight in. 

There are also also various hardware components  for play sets and playground equipment, like this:

Jerk straps are the answer. Bouncy swings are more fun. 

We have those porch swing hooks, once a year I make sure they are still tight but they’ve been good.

Yup.  As noted above:  Specialty hardware made exactly for your application.  Readily available and reasonably priced.

In reply to SVreX :

I agree porch swing hooks are the answer, but note that the branch is 12” in circumference, not diameter. 

In reply to Duke :

You sure?  That’s not what John said in the first post. 

In reply to SVreX :

If you read the first part of his post, he says it is 11 inches around the branch, and the pictures bear that out. But you are right, later he says 12” diameter, I missed that. Though I note that he says “only” 12 inches. I can’t see saying “only” if the branch actually calipered 12”. 

In reply to Duke :

Well, that would be a little smaller than I’d be comfortable with the lag screws. 

The strap style might be better. 

My math and math terms are not that good. Ha. 

Yes, I too have some concerns that lag bolts might not be the answer. Mostly, my concern with using them is I get the drill a little off center I could crack the branch...then there is no swing at all. 

One of my tasks today was taking boxes to recycle. I opened the Montero to find a section of line that I had thrown in there to be a tow/recovery rope if needed this winter.  This was intended to be a jib sheet on a 35 ft sailboat. It's really good stuff. Probably a 5k+ pound strength. A really expensive error about 10 years ago of ordering it too short. 

It's UV coated with a durable exterior coating and though old has spent all its life indoor.  Probably financially one of the more expensive solutions but since it's here doing nothing, one of the cheapest solutions. 

Great ideas came from this thread. Like the straps, I'll tie a bow line knot/hoop into the line then wrap it 3 times around the CIRCUMFERENCE of the limb, each time passing through the hoop. This should give some weight distribution. At the working end of the line I'll tie another bowline/hoop. At that hoop I'll reuse the connector link and attach the existing chain. 

At least, that's the plan in my head. 

Spiking this thread so I can reply when not using thumbs

A double clove hitch might be easier, and it’ll wrap neater... the trick will be setting it so the free end points down

Rust, friction wear, then shear pull out failure because the section available could not support the load after it wore away.

I am not at all a fan of hanging swings from most trees.   Maybe an oak tree but not too many others.   

My neighborhood has lots of them and people swing their little kids in them but for my kids I built a frame out of 4 x 4's, used pivot connections and put galvanized steel bolts all the way through the upper cross beam with flat washers on the top side, no screw in lag bolts for me.  

But I am a structural engineer and can imagine all sorts of failure paths and so try to avoid them.

If you must do this first off don't drill any holes in the branch or insert any lag screws.  You are asking for trouble.  The branch gets weaker and there is the probability the screws will pull out.

Use a proper pivot connection and suspend it with something that is either stainless steel or a UV balanced nylon strap arrangement.   One day a 100 lb kid is going to jump on this.

And keep in mind that in the construction industry for something to be rated to hold up humans it needs to  have at least a rating of at least 10 times the weight of the heaviest person expected to swing from it.   

I'd aim for the strap as dculberson had suggested and go for a softer option than chains. At least if they snap you don't have a hard object falling over your kid.

On another note, John, that rope is best left for the bedroom, not towing. 

Using my strap setup I swing on it and also swing on it with my kids on my lap. Way safer than any bolted thing. Bolts and living trees don’t mix well. 

Timely thread, I need to shore up the tree swing myself, and that strap looks to be worth it.

jharry3 said:

Rust, friction wear, then shear pull out failure because the section available could not support the load after it wore away.

I am not at all a fan of hanging swings from most trees.   Maybe an oak tree but not too many others.   

My neighborhood has lots of them and people swing their little kids in them but for my kids I built a frame out of 4 x 4's, used pivot connections and put galvanized steel bolts all the way through the upper cross beam with flat washers on the top side, no screw in lag bolts for me.  

But I am a structural engineer and can imagine all sorts of failure paths and so try to avoid them.

If you must do this first off don't drill any holes in the branch or insert any lag screws.  You are asking for trouble.  The branch gets weaker and there is the probability the screws will pull out.

Use a proper pivot connection and suspend it with something that is either stainless steel or a UV balanced nylon strap arrangement.   One day a 100 lb kid is going to jump on this.

And keep in mind that in the construction industry for something to be rated to hold up humans it needs to  have at least a rating of at least 10 times the weight of the heaviest person expected to swing from it.   

I’m not arguing, but there are several things in this post that confuse me. 

First off, why is a 4x4 stronger if it’s square than if it’s round?  John’s branch is essentially the same size as your 4x4. As a carpenter, I would suggest that the full round branch is probably stronger than the 4x4. (Not knowing species). For one thing it’s still alive, and not all dried out. The cellular structure had not been messed with by injected chemicals and artificial forced drying processes. Both have the heartwood and center of the annular rings. Why do we have issues with round wood (just because we can’t read it’s characteristics off a span or load table)?

Secondly, I agree about my personal preference regarding lag screws. However, the hardware I showed is rated for 210 lbs. That’s significantly more than John’s kid weighs. 

And third, I’m confused about the 10X safety margin you referenced in the construction industry. All the construction equipment and OSHA guidelines I am familiar with reference only a 4X safety margin. 

I completely understand your ability to envision all the worst possible failure scenarios (and I appreciate it), but these points seem excessive for John’s baby swing. 

I went with porch swing hooks, they have held up just fine for a few years. I also went with polyproylene rope for all-weather durability.  I found some brown stuff that looks like good-old sisal/manilla rope from a distance, giving a classic tree-swing look.  You just have to learn to tie the right knots. 

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.

Also John asked for a more permanent solution - the straps will last for years and years. A 210 pound rated lag screw could be pulled out by an adult sitting on the sure to be swapped in traditional style swing a few years from now. 210 pound rating, per fastener I'm sure, is still not a lot when you think about the amount of strain and jerk they are subjected to. Watch a kid on a swing some time, that chain gets loaded and unloaded pretty hard, frequently. Then throw an adult on the swing too and, well, I just wouldn't do the lag screws at all.

They make some tree wrap protector for use with zip lines.  I think the in-laws' are "tree hugger" brand or something?  I'd use some of that with a bit of wire rope to hold up a hinge like SVreX linked to.  From there just do normal chain down to the swing. 

I built a frame, but that's because we didn't have any good trees for this.