But what size of drill? Was the pilot hole too big? Sheet metal? Too small
vice (not heavy enough)?
Normaly, a stop in one of the T-slots is enough if you can prevent the
vice
from rotating. That stop is just a knurled round, about 100..150 mm long
with a thread at one end and a mating T-slot screw.

I was in a hurry, first mistake. I need a bracket to mount a panel mount
on/off rotating electrical switch. Found a piece of 1/8 x 3" by long AL at
the finger brake. Bent it to a 90 and cut it to length, second mistake (no
way to easily clamp now) Small drill had 1/2" in chuck so I punched and
drilled pilot. Went over to big drill with 1 3/16 bit, clamped on 3' 1"x1"
tube with vice grip and sat it on a small piece of 1" thick metal with a
hole in it on the table. Flimsy set up, but I'm in a hurry. Its the third
mistake that will really get you.

You're right, there's enough pain that I will get a large drill press vise
for this machine and find a way to quickly mount and remove it

Karl