I built a frame to hold 2 26" craftsman 8 drawer bottoms side by side, they each have a 12 drawer top box on them and a hf 7 drawer side cabinet on each end. all of the drawers are full and I have no idea what it all weighs. I will probably go with 6 casters, what do the experts suggest? links to suggestions? thank you.
Then you are going to have to decide how you want to lay the casters out, depending on the maneuverability goals you want for the box. If you put two fixed on one end and 4 swivel it will swing about that one end well, but wide. On the other hand if you put two fixed in the middle and swivel on each end you will have a very nimble cart that will turn about its center point. All swivel and straight line stability will be a challenge. Look at the Kennedy versacart caster options for different ideas. You are probably going to be close to the 1250lb range pretty easily fully loaded. Can your frame handle the bending and torsional loads?