I found the cogs tended to be tilted up a bit when inserted in the pot holder. Being angled would stop them moving freely along the racks, so when I glued them in place I supported them on blocks, as seen here, with the pot upside down and applied some weight from above to persuade them to set in a more or less horizontal way. Don't overdo the weight - you might need to file the holes in the pot holder a little too.