I'm a sucker for this question every time it gets asked, even when I get shot down. :biggrin:
A Jacobs chuck has been mentioned but a Key-less chuck is substantially longer. :biggrin:
If I was at home now, I'd measure a 13mm ( 1/2 inch ) keyless chuck with a 1/2 drill bit in it and a scroll chuck on the headstock and you'd be shocked at just how little space is left.
I've ALWAYS advocated getting the biggest baddest heaviest longest lathe you can afford at the time. You've seen what I attach to mine and perhaps you'll never want to do that. But with a smaller lathe you won't EVER be able to do it either.
There are many many members here that get by with a mini lathe and most often they can come up with resonable good justification for getting it, and to be fair, have made some wonderful items on them.
But hey, Jon, you have a spare bob or two and seem to be inquisitive enough to want to play later on, so splash out and get a 9 x 20:biggrin: