After showing us all those quality second hand ones, how come you went for this?
Alster370 wrote:1.) what depth of cut would I need for an o ring groove on a piston of 19mm?
What's the o-ring inner and outer diameter?
What is the true diameter of the tube it will be riding in?
2.) Am I ok to remove the tail stock so I can work with a longer work piece?
As long as the piece is properly held, and you're working near to the chuck, it should be fine. Consider getting a
steady rest though.
3.) I sometimes get a fairly nasty shock when I have the lathe running and my hand is touching the variable speed control knob, despite it being made of plastic, any thoughts?
Stop using it immediately and have it checked out by a competent electrician. It could be down to static buildup due to friction, but I wouldn't risk it.