# Swingset beam sway advice



## D270 (Mar 27, 2011)

Ok,
So I built a swingset with 2, 2x8's sistered together....

I had my 7 year old (50ish pounds?) swinging in the center position of three swings (span is 11 feet). I notice a little...maybe 3/4" of sway side to side from the swinging motion. I didn't forsee that.
The legs are firmly on the ground...the sway is solely from the beam.
There was a hint of a natural bow to start, but I didn't see that as creating this issue.

I will use 5 inch screws down the length of a 2x? making a "T" if you will. A 2x4 will fit almost exactly the width of the 2, 2x8's...1 1/2+ 1 1/2=3"...vs 3.5" for the 2x4. of course.

So do I cap it lengthwise with a 2x4, will that be enough to stop the sway?

Thanks!


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## PoleCat (Sep 2, 2009)

I would use another 2X8 on top. Just let the excess hang over equal amounts on either side then it will look like it was engineered that way.


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## D270 (Mar 27, 2011)

Frankly with a large overhang, I can't imagine the bugs that will decide to nest there. I figured a 2x4 wouldn't give enough cover to the paper wasps.

I think I can stand on a 2x4 on the 3.5 side and not bend it...

So you think a 2x4 is not enough?


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## de-nagorg (Feb 23, 2014)

I am confused, your sway from side to side, "relative to what"? 

You have a 3 dimensional structure, So it depends on ones vantage point. 

there is left/right, up/down, fore/back. still from what vantage point?

I am not being persnickety, just trying to understand better. 

I would have used a couple more 2x8 in that beam, but I do tend to over build. 


ED


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## joed (Mar 13, 2005)

> I am confused, your sway from side to side, "relative to what"?


I think what he is trying to describe is probably more of a bow happening in the double 2x8 than a sway. The 2x8 is flexing back and forth in the center.

I'm not sure if a 2x4 will give enough backbone to stop the flex. Perhaps one on top AND bottom.


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## D270 (Mar 27, 2011)

Sorry I thought I was clear . 

So it is moving in the bow. So no bow when the swing is vertical and bow backwards as the swing swings backwards and then bows forward as the swing swings forward. Just the beam, not the over all structure.

Usually a 4x6 is used in these playsets, so I lose a 1/2" in that dimension.

So it sounds like a 2x4 on top might be iffy....?


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## de-nagorg (Feb 23, 2014)

Thank you for the clarification, What ever you use to stop the bow will need to clamp both 2x8 together tighter, they are probably slipping a bit, were they glued and screwed together well?

If you decide on another 2x on top it will need to be secured very well to each beam half, to stop the bowing. 

Another alternative would be a channel iron beam, placed on top and securely bolted through both 2x8 . 

It would need to be the width of both 2x8, or 3 inches, and nearly half the depth of the 2x8. and nearly full length. 

ED


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## D270 (Mar 27, 2011)

I'm a bit short on time these days. So I don't have time to get a 2x4x8', or a 2x8"... I found a cedar 2x6x8' I found in the garage so I'm just going to go with it.

I thought about 1/4" lag screws...and I'm sure many will disagree, but I'm going with #9 triple coated deck screws instead. I didn't want to take any more "meat" out of the beam since they are going through the 1 1/2 end on top. If the screws don't hold up...like the cubs..."there's always next year" to try the bigger lags. I'll stagger the screws and predrill best I can.

I'm pretty sure the sistering is ok. Construction adhesive, plus SS wood screws 3" at 18" intervals, with 3/8" bolts through both boards staggered in a "Z" pattern. The beam is 14' but the span with the supports is only 11'...so I was surprised about the motion as the kids were swinging. Oh well.

Anyway...it's way better than what the kids had before...cheapo toysr'us that used 2x4's holding up a 2x6 beam and rope swings. The "picture" on the box looked great at the time, and the price was what we could afford at the time...lesson learned. :-/


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## carpdad (Oct 11, 2010)

Some flexing is no problem. I would stake the legs, minimum. The swing A frames look wide enough, but you never know.


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## taylorjm (Apr 11, 2013)

What are you using to attach the swing chain to the beam?


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## mikegp (Jul 17, 2011)

You designed and built this completely by yourself? That's impressive. From what I can see it looks pretty nice.


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## taylorjm (Apr 11, 2013)

I see you have long bolts that look like they are going through the entire 7+ inches, probably bolting on the swing chain brackets. I think that's causing most of your swaying. Think about this. The swings are going back and forth, transferring the force vertically directly THROUGH that 2x8 the long way. That's going to cause your 2x8 to twist. You sorta gave the swing a direct link to the entire 7" of that beam. Just hold your hand straight up and down, and pretend there's a swing at your wrist and see how your entire hand twists just like that beam would. I think you could fix most of the problem by taking the bolts out, and using lag screws in the swing brackets. That's going to limit the vertical force to want to twist the beam, instead just swing on the bottom of the beam. If that makes sense.


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## taylorjm (Apr 11, 2013)

On my kids swingset, the beam is about 3"x3" and spans about 7'. The swing brackets are lag bolted to the bottom of the beam. There's no twisting at all, or sagging. If I was to bolt those brackets through the beam, it would cause the vertical force to change, and want to twist that 3x3 apart.


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## D270 (Mar 27, 2011)

Yes I built it by myself...probably took 4x as long. I'm just happy the beam didn't fall on me when I only had one end secured. :thumbsup:

Interesting about the "thru-bolts-are-bad" theory. I'm not an engineer so I can't say if it is plausible. I had to get specialty bolts to go all the way through the 2x8s and there lags aren't superior, IMHO. Lags can come out especially after several seasons, and there is a lot of force on them.

I think the issue is the sistered beam. There are no spacers so the beam is twisting as one. The old beam was 2, 2x6s with spacers in between which actually worked to damped the twisting. The span was only 9', 2 swings, and rope instead of chains into eye bolts...should have just done A Rainbow set looking back.

However, the theory is interesting. The swing brackets are basically "hinges," of course, but I could see how there may be a "lever" effect happening. Although I would think lags would not be much different.

I haven't tested it yet but I topped off the beam with a 2x6.

Thanks for all the information.


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## ddawg16 (Aug 15, 2011)

D2....nice job....

I built something similar for my kids a few years ago....but alas, they are older and video games take on more importance....hence, most of it is gone now.



As is, I don't think you have an issue that will cause problems in the future. 

But, you can mitigate some of the flex by putting in a few more screws. It won't help nearly as much as running a board across the top.

Another quick option...put a board from the side (make a triangle) to the middle point. 4 Screws...and you will basically put the deflection at 0


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