A big thank you to John S of Hobnobs fame and to JAZZCNC for their practical help and guidance a few years back. :)
Its had a long and painful birth and many iterations but eventually my son launched his 3D Printer project on Kickstarter a few weeks back.
BTW our little chinese cnc machine (3020 I think it was called, amongst other things) has munched its way through many miles of aluminium and is still in working condition. (only just)