I have made a split ring to hold a part in when remounting. I turn a ring with the inside diameter within 0.003" of the outside diameter of the part. Then cut through the side of it (parallel to the axis) with a saw so it can grip the part enough for turning. This can also work if you dont have enough surface to put in the chuck jaws. The ring distributes the clamping force over a wide enough area to avoid marks. I hope this is clear enough for you to understand. Unfortunately, I dont have any pics at the moment.