I recently built a 4' x 8' workbench with 4"X6" corner posts and 3/4"
plywood for two shelves and a double thickness top. I', using the
shelves for wood storage on one and tool storage on the other. As
you
can tell, the workbench is now very heavy. I am looking for a set of
casters that would mount to the sides of the corner posts, and allow
me to raise and move the table. My Hitachi table saw has similar
casters that have a lever that either raises or lowers the wheels
just
enough to bring legs off the floor. Does anyone know of this type
casters? I've done some searches, but there seems to be a large
variety of casters types. I would like to be able to move the
workbemch without having to remove everything from it first.

Use swinging auxiliary legs:
Mount the casters on a board the width of the table. Mount the board to
the inside of the legs with a hinge at the top so that the casters
swing down to be one-half inch lower than the bottom of the legs. Swing
the board down and clamp it in place long enough to move the table,
then remove the clamps and swing the board back up.

I've never done this, but I've seen it in several plans. You can get
fancy and design the auxiliary legs so the automatically lock in both
positions, so you have ropes to pull, or so they swing into place if
you just lift the end of the table.

--
Steve Bell
New Life Home Improvement
Arlington, TX USA