Warning: Long post depicting tedious work as a noob starts learning about machining. Due to my hand being only mostly healed, and my inexperience, the following took place over many days.
I had a bunch of free 1/4" plate I hoped to turn into strut tower tops. So I cut it into rough hexagons.
Next up, I milled 3/4" holes in them.
Then I turned down some aluminum stock until it was a tight press fit in those 3/4" holes.
drilled and tapped it.
After determining that cutting down the OD was hard, I fell back on my old pal the grinder to get them all close.
Got the outside of all 4 turned down,
and proceeded to screw up trying to cut the ID seven ways to next Sunday.
Eventually, You Tube led me to videos for trepaning (sp?), which is cutting a notch in the face of the work, for an o ring or the like. What I was doing was like if that and parting had a baby. This required I grind a custom tool.
Some finish work with diamond stones, and it got the job done.
The speed equations I found online proved ineffective either due to my ineptitude, lathe capacity, or a combination of the two.
Two days of squealing (the machine, not me, I swear), and being showered in hot, tiny chips ensued. Obviously, I need to improve, but I am thrilled I ended up with useable parts. Learning is fun.
Some quality time with the transfer punches and my Playskool drill press and all four are ready to go. I only had to weld up one hole I drilled wrong when I apparently mistook a bit of schmutz for one of my punch marks.
Here's one of the front ones kind of in situ.