Why aren't there any 4 swivel caster mobile bases out in the market place? All the ones I have seen have 2 fixed and 2 swivel. For very heavy equipment, this becomes a limiting factor, since you have to move your machine back and forth if you go in the direction not supported by the swivel. I remember having to steer my 8" jointer flush with a back wall, just as you would do it trying to parallel park a car in a tight spot.

I know swivel casters are more expensive than fixed ones, but I would gladly pay the difference for the convenience. Or is there any safety (tipping risk) or physics considerations (can't move it in a straight line because all wheels just swivel around) that make them not recommended?

Just wondering....