My shop was getting too crowded, so I put my stationary tools on casters in order to push them against a a wall when not in use. I devised a system for using swivel casters on a hinged arm. When the arm is in the lower position the workbench legs contact the floor and the casters rise out of the way. When the arm is raised into its upper position the casters swing to the floor and lift the legs off the ground. Once I worked out the glitches I used this system on my large tools.
I used 100 lb. Capacity casters, and 2×4 lumber for the arms and caster supports. The supports are secured to the bench legs with heavyweight strap hinges. To hold the arms in the raised position I drilled a hole through each arm and the lower bench rails to accept pole barn nails. There’s no mystery about the bench except that one side of each leg is tapered at the bottom to provide a tight fit for the caster.