Long story short I have a second hand rotary table and independent 4 jaw chuck with an adapter plate. On my first use I got everything setup and started cutting. After a few minutes the mill grabbed the steel and ripped into it, pulling it and the chuck upwards. Although I came out ok, it could have been a major accident.
It should be noted that all of the machine screws were tightened fully, but to my surprise they were slightly long. This allowed a very small gap between the head of the screw and the plate allowing it to "wiggle" a few thousandths or so. The fit on the inner bore of the chuck to the plate is firm enough that you couldn't tell a thing.
Here it was before...
I chucked up some 5/8" brass rod and center drilled it 7/32"
I parted off 4 washers 1/8" thick and cleaned the faces up on 320 grit.
And here it is "after"
I could have alternatively just shortened the screws (or just bought washers!) but this was way more fun as well as more practice for me.
It did raise the head of the screw off the adapter plate about 1/16" but that's no concern with my current setup or anything in the near future. Anyways, hope this helps out someone else in the future save some fingers.