Here is a quick, easy and cheep way to build them.
I took a plastic wheel Bachmann wheel set, pulled off the wheels and placed the back
on the steel axle in reversed order. The steel axle flush with the plastic sleeve. Fill in
between the flanges with small strip wood. Now the sides. Glue two layers of strip
wood perpendicular to each other in a 3" by 3" square. Make two. Using a 2 1/2" hole
saw cut out a circle. The hole in the center will be for the axles to stick out.
You can add heavy wire to finish the spool. You can weather the spool if you wish.
John F