I want to stress safety first and foremost. Please wear all appropriate protective gear (eye and ear particularly) and know how to use the tools safely. Also, please call 811 before you start digging. It's a free service and it will prevent you from having a potentially very bad day when you accidentally cut through power cables!
I also want to stress that this is just one way of putting these structures together, there are many other ways to do this. This is also a fairly inexpensive way of doing it as I use mostly pressure treated lumber with the exception of the cedar cladding on the posts and and no fancy connectors, just screws, nails and bolts. I do use power tools for most of this but it could potentially be done with hand tools, just a lot slower (and frankly, I'm getting too old to put that much effort into a project).
Okay, on with the show. (By the way, any of the posts that look bent in the photos is due to my phone pictures and are not ACTUALLY bent)
With a plan firmly in mind, I am going to use 4" x 4" x 10' PT (pressure treated) posts with the top of the structure being 5/4 x 6" PT decking boards. I like the decking boards because the edges are pre-rounded and I think 2" x 6" boards are just too chunky looking for this application.
With your area laid out, break out your post hole digger and get to it.
The general rule of thumb for the burial depth of poles is 10% of the length of the pole plus 2'. That's probably overkill for something like this but, as it's going to be a swing, I'll err on the safe side. If you look closely, the marks on the post hole digger show that I'm at about 40" deep.
This gives me 3' burial with about 4" of stone added to the bottom of the hole. This stone layer will help with keeping the pole from rotting for a very long time. I use these marble chips because I had them on hand and they're fairly cheap.
Even though the posts are pressure treated I still like to add an additional layer of protection. I paint on a layer of Coppercoat (and yes, I know it says for NON pressure treated, but I'm paranoid, so there you go) You can skip this step as this stuff is NASTY! If you do use it, use it only outside and with a respirator. You can see on the right where the color is slightly greener where I've painted the portion that will be buried.
Okay, so now set the post in the hole. (You can now brace the post with boards and stakes in the ground to level it, but I just get my son to hold it in place fairly close, as you have some leeway to level it when pouring the concrete) You will be pouring fast setting concrete into the hole around the pole in it's dry state. I spray the hole with a hose to saturate the walls because in Florida, the hole will NEVER fill 1/3 full with water. Then pour in your dry concrete to fill the hole to about 2/3. I spray more water in the hole and use a length of rebar (really anything will do even a 1" x 2" piece of wood) just to mix the water and concrete by stabbing into it repeatedly. This will also get out air pockets which would weaken the foundation. At this point, put your longest level on the side of the pole on two adjacent sides to make sure this sucker is straight. Fill the hole the rest of the way and slightly overfill, spray with water and repeat the process. Again, at this point, make sure your post is level on two adjacent sides. When you have the hole filled and some excess above the top of the hole, use anything like a trowel or putty knife to put a slight slope in the top of the foundation so that water drains away from your post. Make sure to do this quickly before the concrete sets. (See the pictures)
At this point it's just repeating the process for as many posts as you need. I used 4 in this case and this is what I ended up with. (Please ignore the neighbors house, we will be putting up a fence shortly, but that's another story)
Stop here, pat yourself on the back and have a cold beverage if that's your thing, because the really back breaking stuff is done! Yay! Ideally, let this dry overnight. (You could probably move on the same day because this concrete does dry pretty quickly, but I don't recommend it)
Once the foundations are dry, run a bead of silicone where the concrete and the post come into contact. I just use my finger to smooth it out. Once again, this is for increasing the longevity of the posts.
Now we are going to wrap the poles in cedar to make them look a pretty. I'm using 1" x 4" cedar to get a particular look, which I'll explain in a bit. I use a clamp to put these on the posts, 1/2" to 3/4" above the top of the concrete, then mark the tops for cutting. Then I use a construction adhesive on the back of the cedar and clamp it in place on the post.
Finally, use stainless steel nails to permanently attach the boards.
Repeat for the rest of the boards and posts.
Now onto the fun artistic stuff where you can put some character in this project.
A lot of the following is very 'seat of your pants', figure it out as you go kind of things. Like, what design do you want for the ends of the horizontal boards and also, how much you would like them to overhang each other. I actually have mine sticking out further in the front of the structure than the back, just in case we ever want to hang plants from them.
Here's my high tech design and cutting method.
Yep, I used an old plastic pot.
Then I cut it out with a jigsaw and smooth over the edges with a palm sander.
They, then get two coats of a semi transparent stain and sealer that I had tinted the blue-green color.
Once both ends are cut, I clamp a board on each side of the post and drill through the whole thing for the lag bolts. The pictures speak better than I can.
And yes, the spider man coffee mug is vital!
Oh, and a little technique I use to keep your drilling and bolts nice and straight at 90 degrees:
Drill a shallow starter hole.
You then place something that you are sure is 90 degrees at the hole. (I use a framing square because it's deep)
Put your drill bit tip into the hole so that it is against both sides at the bottom of the square.
Then move the drill until the upper portion of the bit is flush against both sides of the 90 degree object. Now you should be lined up perfectly for a 90 degree hole.
And here are the front and back lower braces in place.
On to the top boards that go across the boards we just put up. The first one can be a bit tricky, but after that they're pretty much identical.
I cut the board to length and shape and sand the ends just like the first boards.
Set one in place and mark where the slots will need to go.
Break out the jigsaw and I use a chisel to get out the chunks. You can see the blue tape on my square that I use to mark the depth I want these at so they are all the same. Then stain them.
I then put wood glue on the contact points and persuade them into place with a rubber mallet. The boards that are on either side of the posts can then be screwed directly to the posts.
The others are basically the same except you will have to drill from the top through the board and into the bottom one for a long screw. But if you use the 90 degree method above, it shouldn't be an issue.
And here's what you end up with.
You can see I started on a trellis that uses basically the same methods.
And here's the privacy screen that was built exactly the same way. I still need to add the white quarter-round pvc between the cedar board edges on the swing structure like is shown here on the privacy screen. But that's just attached with the same construction adhesive and I didn't see a need to go over it.
As you can see, this can be applied in many ways to many projects. Just use some imagination.
Hope I didn't bore you, I know I can get a bit long winded. If anyone has any questions, please feel free to contact me. I hope you enjoyed.