[scott_vt]

Good Afternoon BHD,
On long shafts that are to large in diameter to fit inside the headstock you can use what is called a steady rest. It is a device that has three ball bearings that the shaft runs on and it is clamped to the ways on the bed, obviously the two lower bearings need to be adjusted properly and then the top of the steady rest is flipped down and the top bearing is then adjusted. The old time steady rests had brass supports rather than ball bearings.

In the event that the shaft has a rough finish not suitable for using a steady rest, you could use a vee block on a Bridgeport miller and hang the shaft off of the side of the table and swivel the head on the miller, and then use a dial indicator to indicate the end of the shaft !

There are some other methods but thats the just of it !