These are the slip rolls that were made after reading Geo H Thomas's'Workshop Practice' manual although quite small, approximately 10" capacity they have worked much better than I expected, they were used to roll the upper and lower sections of the small boiler elsewhere on this site.

  Here the top roller is removed showing the latching mechanism, both ends were fastened together for machining operations to ensure that the rolls remain parallel, the bottom roller runs in plain phosphor bronze bearings. 

I thought that I could get away with a gearing system shown here, this really only works up to a point and does not provide a smooth enough drive, these will be replaced with a train of four spur gears when I get around to it.