I helped a friend but together a couple poles for a clothesline.
They wanted it to be about six feet tall, and the top part to be about three feet wide, so we grabbed four 4x4" square posts that were eight feet long.
Two of them would be the vertical posts.
One of them would make the two top horizontal pieces.
And the last one would make the four 45° support pieces.
Step 1: Joinery
We decided to join the top piece to the vertical piece with a half-lap joint. I set my circular saw to cut half the depth of the post and used a speed square as a guide to make repeated cuts in the area we wanted to remove.
We then used a hammer and chisel to remove the slivers, and cleaned up the joint with a couple hand planes and a rasp.
We did this for the center of the horizontal pieces, and the top of the vertical pieces.
Step 2: Eyebolts and Diagonal Braces
We went ahead and drilled the holes for the eyelet screws that would hold the line.
We decided it would look good if the diagonal braces were 17" long on the outside, so I went ahead and rough cut the last post into 19" sections so that everything would be easier to work with. I then used my miter saw to cut 45° angles on the ends and bring the pieces to their final lengths.
Step 3: Assembly
A few days later I showed up at my friends' house to assemble everything and put the poles in the ground.
We started with the top piece. We put a glob of construction adhesive on the inside of the joint. I'm not sure if this will actually help at all, but I figured it couldn't hurt and might have a better chance of sticking to the pressure treated wood than traditional yellow wood glue. We used a speed square to make sure the vertical and horizontal pieces were perpendicular, and zipped three decking screws in from either side
We used the same basic construction for the diagonal pieces: construction adhesive and long decking screws.
Step 4: Setting the Poles in the Ground
We went ahead and put in the eyelets while the poles were lying down and started digging the holes. Luckily we didn't hit any large rocks or major obstructions, and didn't have to trim the poles short. We ended up going down 20 inches, using a post hole digger and a shovel.
We used some scrap pieces of wood to make supports and stakes that would hold the posts level and in place while the concrete cured. Each hole ended up getting about 3/4 of a bag of concrete.
Step 5: Done!
Once the concrete was cured, my friend removed the supports and the poles were ready to string up!