Hi Sub, thanks. Yes I've gone through a few end caps already
. Still its all practice I guess. Yes I will be using an oring in axial compression. Its a pretty small chinese lathe. About 75mm from the centre of the chuck to the bed so 150mm swing. My tube is 100mm od. Yes even reversing the jaws on the chuck, I wasn't able to get them wide enough so I used a mandrel. I made the endcaps as 1 piece out of thicker pvc, but I think is may be easier to make it up as 2 pieces and glue them together