Step 1: Get some 25mm ID / 50mm OD bearings
Prise the side seals off and scoop out all the grease, then rinse the bearings out with some diesel or turpentine to make them spin easier, then pop the seals back in. They should spin easily now.
Head down to the hardware store and find a cheap broomstick handle that just fits inside the bearings. Dont worry if its a tight fit.
While you're at the store buy some 50mm (inner diameter) PVC tube and 2 large buckets (I found about 20 litres ideal).Also uy some long screws - I used plaster screws at least 50mm long.
Step 2: Make the shaft
Tap 2 bearings to be close to the center of the broom handle, then slide the 2 lengths of the PVC tube and tap it down so its a nice tight fit, then tap another bearing into each open end of the tube.
I also fitted an end cap to one of the tube ends, as well as a bell shaped fitting to keep the rain out (see picture). Screw the top piece to the broom handle in the center so its fixed to the broom handle. The broom handle has now become the center drive shaft.
Check out the video - you now have a free spinning drive shaft - I have a small piece of dowel I drilled into the bottom of the broom shaft to show rotation while clamped in the vise.