Top and bottom end pieces are of 20mm thickness with a recess for fixing bolts. The centre part can be z scaled to the correct dimension for whichever you choose. It is a nominal 25mm high so increase it or print multiples as you wish. Continuous roll of velcro backed sanding roll is widely available from ebay or Amazon at 115mm wide. At this dimension for the drum a 5 metre length will provide 20 renewals of the sanding medium

(I printed 3 of 25mm and 2 at 20 giving a total of 115mm so I could use up my roll ends without sitting around to do filament changes) The pieces were fixed with a length of threaded rod and epoxy using nyloc bolts, Cut the rod long enough to be secured in the chuck of the drill. 

Put in drill and lightly sand exterior to remove surface glaze before sticking or bonding Velcro to the outer surface. 

Printed with PETG at a layer height of 0.3mm with 0.4mm nozzle I used 30% infill with 6 perimeters for extra wall strength but no top and bottom layers for the centre sections so the epoxy could flow a little deeper into the layers. Top and bottom sections were given a 4 base layers and the open top again. Printing with a larger nozzle size will of course significantly reduce print times and the need for as many perimeters, but at the time of making I didn't have that option.

Keep in mind this is mainly for light sanding as a pillar drill will not have bearings intended for side loads.