I started off with three 4x4 pieces of lumber. They typically come in 8' lengths, so that's what I got. One thing you need to be aware of is that a 4x4 is not actually 4" by 4". It's 3 1/2" by 3 1/2". Why? I'm not sure. I was told at one point that it's because when the lumber is cut, it's cut as a 4x4 but then in the processing and smoothing, it's trimmed and comes out smaller. Whether or not that's true? I don't know.
Anyway.....the first thing that I did was take one of the 4x4's and cut it in half, so it was now in 2 lengths that were each 4' long. Then I found the center of each one and made a small mark, then drew lines that were 1 3/4" out from each side of that mark. By doing that, I had marked the 3 1/2" wide spot that the vertical post would eventually fit into, and it would be centered on the horizontal crossbar.
Then I took my circular saw and set the blade to about 1/2" and cut grooves into the wood about 1/4" apart. I laid them side by side and cut through both of them at the same time just to make life easier.
Then I used a hammer and chisel and chiseled out the part that I had grooved, which left a 3 1/2" wide notch in the wood that was about 1/2" deep. The vertical pole will now fit in that notch, giving the whole thing a little more stability. You don't want to make the notch too deep, or else it will weaken the crossbar and it can split in the middle.
Make sure it fits.
I measured down 5" from the top of the vertical piece and made a line, and then lined the crossbar up just under that line. I had carriage bolts to hold the two pieces together, and used a long drill bit to drill through both pieces, inserted the bolt with washers and tightened them together with a nut.
I had purchased eye bolts to use to attach the ropes, and chose to get ones that were long enough to go the entire way through the crossbar, but you can always use shorter ones that just screw into the wood without going the whole way through. I measured about 4" in from each end of the crossbar and then spaced 4 eye bolts across it, drilled holes the entire way through, inserted them and tightened them with a nut and washer.
At this point the poles were done.
The Dude and I had measured out where we wanted to put them earlier in the day and I marked the spots with spray paint. I dug holes about 18" deep and then stood the pole in it to see if I could reach the top or not. I wanted them to be fairly high so that when I hang sheets and comforters, they won't drag on the ground, but I also didn't want them to be so high that I couldn't reach them. So I made the crossbars as high as I could comfortably reach and used a quick concrete mix to anchor them in place. I used a level to make sure that they were standing straight(ish) and propped them so that they wouldn't fall before the concrete started to set.
I ran into some technical difficulties in the process - like I somehow managed to jam the first drill bit into the head of the drill and it wouldn't come out, no matter what I did. Finally after fighting with it for about 45 minutes I gave up and took it to the local hardware store, where the owner was able to get the bit out in about 2.5 seconds. Not counting that, from beginning to end the whole thing probably took less than 3 hours. I'll put the rope on tomorrow after I know that the concrete is good and set. I also plan to put some decorative bricks around the bottom of the poles, but that'll wait until tomorrow at least.
Like I said, super simple and quick to do. I need to dig out the receipts and figure out exactly how much I paid - I'd say that it was under $50. If you're looking to do something like this, there are about a gajillion plans for them online - I had scoped them out and just combined ideas that I liked and came up with this one and so far, it's worked. We'll just have to see what happens when I do my first load of laundry with them.