Thread: What size box section should I use?

I think that 50mm box by 3mm, Plus that brace. Would hold any human. But I think what u have drawn there would be ideal. That looks good.
Scott

Mark, nice sketching.

One thing to watch is fatigue on the brace - also there'll be a lot of twisting forces on the upright pole - so make sure the mounting bolts go right through the wood. Make sure the wooden pole is solid and well bolted to the rest of the structure. You'll be amazed at how much stress a swing will put on your structure.

As far as the box section goes, I would personally over-engineer by a big factor. I agree that what you've drawn looks good, so something like 75 x 75 x 4mm would be my choice, but maybe you could use C section (or maybe even T) rather than a full box if you are really worried about weight.

Cheers

- Mick

One thing you have to account for is an adult sitting on it, and it will happen.
I would go for 65x65x3mm and that size is used in the second stage of a 2 ton engine crane so it should be strong enough. For the flat bar I would go with something like 75x5-6mm and the support brace 50x50x3. I would also tie the brace into the hand rail with a bolt to help any sideways movement. As Mick said have the bolts running right through the timber.
You can buy dome nuts from the hardware shop and this will save any sharp threads being exposed for your daughter or friends to get caught up on. Also with the 2 flat bars you pictured, you have to think about the kids could get there leg caught in between them.
Like said above, nice drawing.

Dave

Originally Posted by Dave J

Also with the 2 flat bars you pictured, you have to think about the kids could get there leg caught in between them.

Hi Dave Good point - maybe the brace would be better as round pipe (say 50x4mm). One less corner for the kids to hit their heads on and would be just as strong if not stronger. Cheers - Mick

Originally Posted by WelderMick

Hi Dave Good point - maybe the brace would be better as round pipe (say 50x4mm). One less corner for the kids to hit their heads on and would be just as strong if not stronger. Cheers - Mick

Pipe might be better, I was just thinking square so when it's bolted to the rail it will has the 2 flats bolted together. The timber rails are square so it would match in with them as well once it was all painted.
They also have cattle rail which is a nice oval shape and looks good, but you would need somewhere to buy an off cut and not the whole length of it.

Dave

Hi Mark,

I think the cantilever will be strong enough to carry the weight, and Dave's modifications will make it safer.

The thing I'm a bit unsure about is that there is nothing to stop the cantilever arm from moving back and forward. (as WelderMick said) All the load is going onto the join on that 90mm square wooden post.

The usual way of supporting a swing is an A frame on either side of the swing.

When you get it installed, try it with an Adult on the swing and watch to see how much it moves.

I can't suggest a good solution without knowing what's underneath the swing. Is it possible to do an A frame?

Regards
Ray

I would be looking at pipe and an A frame as well, would be a lot less stress on your structure and won't fail. I think it would look better as well.

Thanks for all your suggestions guys.

In response to some of the points made:

For the plate I was originally thinking 5mm, but dialled it back to 3mm. Maybe that's up to 5mm again . And yes, through bolts all the way with a dome cap on the side away from swing and the nuts up against the steel plate (The other side of the post is the slide, so best to keep anything sharp away from that!)

Yes, an A-frame would be ideal, however my back yard has very limited space, and putting an A-frame there would pretty much cut my usable lawn space in half!

The post is one of the 4 supporting posts for the whole structure, and is set in concrete footings. The whole structure is an open frame and there is no bracing. This is not a problem at the moment, however I think once the swing goes on I will need to add some. (No problem with the kids, but with my weight holding the top of the post and applying some hefty rocking force, there is a small amount of lateral movement).

I'm definitely rethinking the support, especially after the points made about a trapping hazard. Box section or tubing absolutely a better option.

Thanks also for the comments on the sketch. I figured an hour or so painting a picture would be so much easier than trying to put it all into words!

Maybe you could put a horizontal brace between the swing arm and one of your other posts? Then add an additional brace between the 2 posts themselves. As long as your posts are well anchored in the ground then this would be a lot more stable than the initial concept.

The cross brace could actually be a 'feature' - in other words a hanging bar.

Cheers - Mick

i would also get rid of the two flats as a brace,A little arm can get caught up in that spaceand rhs will be substantialy stronger.

Originally Posted by WelderMick

Maybe you could put a horizontal brace between the swing arm and one of your other posts? Then add an additional brace between the 2 posts themselves. As long as your posts are well anchored in the ground then this would be a lot more stable than the initial concept.

The cross brace could actually be a 'feature' - in other words a hanging bar.

Like the idea, but not practical for me . The posts are 1.5m apart, and the one for the swing is the only one that extends to that height - the others are only 700m high and a cross brace like in your picture would be more of a hazard than a feature :/

What about not using a brace, and then have a post going down the side of the outside handrail, and concreted into the ground but still bolted to the handrail. This would take the weight off the timber post and make the whole structure more rigid.

Dave

Or is something like this feasible?