Many thanks George, Ned , Anthony and DoN, all good ideas I had not thought
of. I spent an hour or so investigating chuck stops, spindle stops, spiders
etc. I'm leaning toward the idea of a stop located in the spindle and clamp
the work with the 3 jaw. This will give me a greater range of stop position
location - from partway along the chuck jaws to back inside the spindle for
longer jobs.

I wasn't too sure if a chuck spider was a beer & ice cream thing, I found
some good pictures here that clarified it for me:
http://bbs.homeshopmachinist.net/showthread.php?t=24007

The help and advice you guys provide is really appreciated.

best regards
r.