Karl Townsend wrote:
Ditto what Jon said about rigidity. I also like keys on the vise bottom.
Just slide the vise in the slots and its square. Saves a lot of setup time.

I generally align the vise jaws to the X axis within .001" I rarely put
the vise body along the X where the keys could fit the slots, as so much
of the time the long edge of the parts is parallel to the jaws. Due to
a small Bridgeport (the oldest round-ram turret millers had a 9" travel
on the Y axis, and do to some goofs in my retrofit, I now have only
about 7.5 inches travel that way). I have a later Bridgeport 12" knee,
but need to come up with a number of parts to retrofit it on my
machine. I wouldn't trust the keys for alignment unless I had tweaked
them myself. The table slots are not precision machined parallel to the
ways, at least on my machine.

Jon