When I make a cylinder, I don't mitre anything. Just put your disc inside the tube and sew. Well, it's not quite that easy, like they said, you need more holes on the disc than on the tube. If I wanted to do 8 stitches per inch on the tube, I would mark the disc for 9, it probably won't work out perfectly, just keep an eye on things and when the holes don't line up, go through a hole twice, just like lacing around a corner on a wallet, you make up space once in a while.
Have fun,
Kevin