1. Cable drum
2. 25.4mm dowel
4. Clear coat
5 3 castors
First step in my case was to insert a replacement board as one had come away. Luckily I had some thin pallet boards that were pretty much an exact fit, I just glued and clamped this and then used a jigsaw to shape it.
Second step is to tidy up any protruding nails, either punching them in, or extracting them if you can. This requires a bit of judgement.
step 3 is to sand all over I went from 80 to 120 to 180 grit,
Step 4 is then to round over the edges and any sharp points. I could have used a router but just decided to use a detail sander
Next step is to decide which side is best to use as the top. In my case it was fairly easy as the replacement plank meant the other side was better as the top.
Now, turn your drum over so the bottom side is facing up,
now measure the height of the gap between the underside of the 'top' and the underside of the bottom. Now cut your dowel into 6 pieces of that length. You could do more uprights if you like.
Now measure the distance from the core of the drum to the edge and divide by 2. You can now measure in from the edge and mark where to drill the holes for the dowels, obviously spacing these equally.
I used a spade bit to drill the holes through the underside of the cable drum and then simply tapped the dowels through until they hit the 'top'. They felt tight enough not to require securing at the other end.
Now fix your castors in place - space them equally a couple of inches in from the edge. Now turn it over and it starts to look like the finished product.
Once done, it's time to start painting! Go for your life.
On reflection I probably should have used thinner dowel and more of them to help books stay upright, but that would make painting a bit trickier.