After struggling using the cardboard sided spools for a while, it has become apparent that the filament is being dragged towards the inside of the spool, causing jamming. I found online someone who had used acrylic discs to stop the cardboard from flexing. Removing the cardboard sides of the spools, and replacing them with acryllic discs, has proved to be a much more reliable delivery system. The acrylic discs cost £3 each to be laser cut from the drawings included. To assemble this also requires an M10 x 50mm countersunk bolt and nylock nut, and 2 x m4 x 50mm countersunk bolts with nylock nuts. You remove one side of the cardboard spool, fit the acrylic disk with printed bobbin through the centre of the spool, then remove the other side of the cardboard spool, and bolt on the secont piece of acrylic. It is not as complicated as it sounds, and once assembled makes a very sturdy piece. It is definately worth the effort, IMHO!