I've posted pictures, hopefully pretty self explanatory. The pictures aren't exactly what I describe. Again, just what I was able to work up as an example given materials I already had available. One should be able to build one of these for under $20 in materials. Not really sure how much load this will hold and still roll easily. I put a hockey stick (it was close at hand) through it, placed it on the floor and pushed down pretty hard and it rolled easily. If more weight bearing capacity is desired, one might fill in the PEX rollers with something. I've been told that one can buy 3/8 OD fiberglass electric fence posts. Those would work well for filling the PEX.
Step 1: Materials
QTY 1 - 4" PVC toilet flange (hello easy mounting!)
QTY 1 - length of 3" PVC pipe
QTY 2 - Rings cut from 3" PVC fitting, doesn't matter what, buy one you can cut two rings from. (note, cap shown in photos as it is what I had) Actually, a cap might be good if the 'axle' doesn't happen to be 3", you can drill/cut an appropriately sized hole in the cap.
QTY 1 - 5' length of 3/8ID PEX tubing (I actually didn't have this, I paid something like $2 for it. It happens to be 1/2 OD)
QTY 2 -Some sort of rigid-ish plastic sheet like a binder cover, piece of plastic paneling, side of a rubbermaid tub, etc. (not in pictures, thought about this later - keeps assembly together)
Step 2: Assembly
Cut the PEX tubing into 25 approximately 1-inch lengths (a scissor like plastic tubing cutter works quite well).
Cut two washers from the plastic sheet ID approx. 3.5 inches (fits over 3" pipe - trace it), OD approx 4.75 inches (slightly larger than ID of toilet flange trace, then freehand slightly larger). No need to be too pretty, hack away.
Glue one 3" PVC fitting ring to one end of the 3" pipe. Place one of your washers over the pipe. Place assembly through the toilet flange and gently bump the washer up against the end of the flange. Mark the length of the pipe where it exits the other side of the flange. Remove, add the thickness of your other washer and 3" fitting ring and cut the pipe there. Place the 3" pipe through the toilet flange again. Set down on workbench, arrange the pieces of PEX in the gap between the pipe and flange. Add the other washer, mask the washer and toilet flange. Glue the other 3" fitting ring onto the pipe. Remove masking tape, done.
Step 3: Use
I originally came up with this as an acquaintance was looking for a bearing to use for a roller furling sail on a small boat. The idea was the mast would stick through it and be rotated to furl the sail.
Other possible uses:
Wheel bearing for a beach dolly for a small boat.
Bearings for a tumbling compost bin.
Bearings for a garden cart.
Step 4: Other Sizes
Pipe Sizes: http://www.engineeringtoolbox.com/pvc-cpvc-pipes-dimensions-d_795.html