Painful Learning Experience

Painful only on time. I tried to get around that problem that my mill vise could not hold the vise in an orientation for side milling the workpiece to .620" so I put so that I could face mill it to that width...

That should have been easy: slice .001" per pass at low speed.  But instead cutting on the 1/8" wall just bounced everything around enough to knock it out of the vise. So I went back to the chop saw and worked very had to make a slice. 625". I got .6".  Close enough.

As i was writing this is realized another method that I did not try but I might try tomorrow just to see if it works. Put the 4" wide piece in the vise with half of it above jaws. Side mill to width. Turn it upside down. Repeat.

If I do this again, I will use 1/4" wall.

That approach also did not work. Trying to mill such thin material just sets the material to vibrating, which simply shakes it loose from the vise and causes the vise to shake loose from the clamps to the mill table.