This type of swing structure you sometimes see at swap meets or during Arbor Days where carpenters display their craftsmanship. This type of swing is a bit different configuration than your typical swing set. The design presents a bit of class and is ideal for any quiet area. The lumber I used was cedar. It is not only more durable but is also lighter than treated lumber. This type of wood is ideal if you want to show off the wood grains when stained. The posts were 4"x4"x8' and I also utilized 2"x3" boards as well.
The bolts that I use were 6"x1/4" Galvanized. In order to conceal the hardware, predrill the holes larger than the size of the bolt head. In this case, I use 1/2" drill bit to allow enough room for the use of a wrench. Careful not to tighten the bolt too much otherwise, you will strip the thread created in the wood.
The length of the support will depend on whether you will be attaching one or two swings. Use braces as much as possible when constructing this frame because you don't get a second chance when you start drilling the holes for the bolts. This particular structure is designed for two swings. The height was initially set at 7 feet but later modified to 6 feet. It is best that the frame be too high than too short. This way you can make the necessary adjustments based on the average height of the persons that will be using it.
The angel of the bottom support will also depend on the length of the structure. This one was 8 feet long to compensate for the two swings. I used a 2"x4" board to simulate the flush of the bottom. If the swing is place on a foundation surface, you will need to make adjustments to that area since no foundation is completely level.
This is the structure initially at 7 feet height and I stained it with a brand named Ready Seal with the color of Transparent Redwood. The wood grain dramatically stood out. Since you would not be using any caulking to cover up any discrepancies, it is very important that your cuts be as exact as possible. If you can, use a Miter Saw.
Though the transparent stain accentuated the luster of the wood grain, the owner preferred a solid color to blend in with the existing scheme of the home. The last two photos is the finished product with the height reduced to 6 feet.
This swing will take one to two days with trial and error. Once you build it the first time, you will look back and think, it was not that difficult. As in any project the most hardest part is getting started. Once you put your mind to it, there is nothing you can't do.