Great point! I was picturing in my head that Yakima was having problems with the joints between the segment pieces instead of between the layers. It drum sander is the way to go for jointing between the layers. A smooth cut with the mitre saw will help with jointing the segment pieces within a particular layer. I guess I didn't think about his post carefully enough. My Bad.
Although I have a nice drum sander I rarley use it to flaten rings. I just sand small and medium rings on a disc sander and you can make one for your lathe out of plywood real easy, a 12" piece screwed to a face plate with a adhesive disk placed on it.If you have cole jaws you can place bolts in backwards and grip the ring,turn it with a gouge and a square end scraper,use a straight edge to check for flatness across the ring.I take a straight board and put two 6" PSA disks on it so they will sand each side or the ring while it is spinning slowly on the lathe. Works great. Use 80 grit, nothing courser or the glue line might show. Hope this helps. There is a picture in my gallery of a ring griped on the cole jaws this way. http://www.turnwood.net/Photopost/showphoto.php/photo/3371/sort/1/cat/500/page/1 Freddie
I also disc sand rings on a rig made for the lathe like Freddie. The only thing diffrent is my 14" sanding disc is mounted on the vacuum chuck (which is another 14" disc with a thin rubber applied to the face) I have 2 discs, one 80 grit and one 100. I like to sand only one side and mount the ring and true up the other after its been mounted.
Drum sanders do work but can leave a bit of "snipe" unless you use sacraficial boards leading and trailing the ring,
BTW very nice piece Yak!!