I think I've shared this before but I got some good pictures of it this week to explain it.
Ok maybe it's just me but I grew weary of taking a standard nut, welding it to the back of a plate through a hole and then no matter how hard I tried always having the bolt drag on the sides of the hole in the plate because my nut is slightly non-concentric.
So here is how I have solved this problem.
Step 1 drill the hole in the plate oversized to just under the flat-flat diameter of the nut you are using. (Example 1/4-28 nut is 7/16 Wrench. I use a ~3/8 hole).
Step 2 thread the nut onto the end of a bolt that puts the grip length shorter then your lathe jaws.
Step 3 chuck on a 3 jaw chuck with 1/2 the nut just poking out on lathe. The bolt aligns the nut to the lathe and retains it well vs trying to chuck just a nut.
Step 4 turn a small lip on the nut. The exact OD and depth of this lip are not critical. I tend to just machine off the rounded bottom portion of the nut and only machine a depth that is only around the lead in of the threads. You don't want to go to deep because you want to keep good meat on the nut. Your turning needs to stay above the major diameter of the thread which is why just a bit under the flat-flat is a good start.
Now the flange you have created will stick into your plate and ensure your nut is concentric with the hole in the plate. Weld the nut on with whatever method you wish.
I'm sure most of you already knew/do this. It took me way to long to start doing this so I am hoping I can save someone frustration. I also know actual pre-made Flanged weld nuts are made for this but they are not $2.99/lb.
