I built a steel snake.
I used 1 1/4" receiver tube (for trailer hitch) as a vertical receiver for 1 1/4" square that is an adjustable upright. This is mounted to lathe bed with a flat plate bolted thru bed.
For steel snake portion - 1" square for about 9", bolted up to 1" square for 12", then down to 1" square for 6". This allows entire arm to swivel over top of vertical mounting - so you are not restricted as to which side of upright you are on.
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Swivel points are thrust bearings with 3/8" bolts as pin with captive nut.
Just make sure drilled holes are plumb and you are in business.